The human body is the structure of a

human being Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedality, bipedalism and exceptional cognitive skills due to a large and complex Human brain, brain. This has enabled the development of ad ...

. It is composed of many different types of cells that together create tissues and subsequently

organ systems An organ system is a biological system consisting of a group of organs that work together to perform one or more functions. Each organ has a specialized role in a plant or animal body, and is made up of distinct tissues. Plants Plants have ...

. They ensure

homeostasis In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...

and the viability of the human body. It comprises a

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...

hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and f ...

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

, trunk (which includes the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

and

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

arm In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...

s and

hands A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each " ...

legs A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ...

and

feet The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...

. The study of the human body involves

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...

and

embryology Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, '' -logia'') is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos and ...

. The body varies anatomically in known ways. Physiology focuses on the systems and organs of the human body and their functions. Many systems and mechanisms interact in order to maintain

, with safe levels of substances such as sugar and oxygen in the blood. The body is studied by

health professional A health professional, healthcare professional, or healthcare worker (sometimes abbreviated HCW) is a provider of health care treatment and advice based on formal training and experience. The field includes those who work as a nurse, physician (suc ...

s, physiologists, anatomists, and by artists to assist them in their work.

Composition

The human body is composed of elements including

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

and

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

. These elements reside in trillions of cells and non-cellular components of the body. The adult male body is about 60%

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

for a total water content of some . This is made up of about of extracellular fluid including about of blood plasma and about of

interstitial fluid In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a lower ...

, and about of fluid inside cells. The content, acidity and composition of the water inside and outside cells is carefully maintained. The main electrolytes in body water outside cells are

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

and

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...

, whereas within cells it is

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

and other

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...

Cells

The body contains trillions of cells, the fundamental unit of life. At maturity, there are roughly 3037trillion cells in the body, an estimate arrived at by totaling the cell numbers of all the

organs In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a f ...

of the body and

cell types A cell type is a classification used to identify cells that share morphological or phenotypical features. A multicellular organism may contain cells of a number of widely differing and specialized cell types, such as muscle cells and skin cells, ...

. The body is also host to about the same number of non-human cells as well as

multicellular organisms A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- ...

which reside in the

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...

and on the skin. Not all parts of the body are made from cells. Cells sit in an

extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...

that consists of proteins such as

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...

, surrounded by extracellular fluids. Of the weight of an average human body, nearly is non-human cells or non-cellular material such as bone and connective tissue.

Genome

Cells in the body function because of DNA. DNA sits within the nucleus of a cell. Here, parts of DNA are copied and sent to the body of the cell via

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

. The RNA is then used to create

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s which form the basis for cells, their activity, and their products. Proteins dictate cell function and gene expression, a cell is able to self-regulate by the amount of proteins produced. However, not all cells have DNA; some cells such as mature

red blood cells Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...

lose their nucleus as they mature.

Tissues

The body consists of many different types of tissue, defined as cells that act with a specialised function. The study of tissues is called

and often occurs with a

microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...

. The body consists of four main types of tissues. These are lining cells (

epithelia Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

nerve tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...

and

muscle tissue Muscle tissue (or muscular tissue) is soft tissue that makes up the different types of muscles in most animals, and give the ability of muscles to contract. Muscle tissue is formed during embryonic development, in a process known as myogenesis. Mu ...

. Cells that lie on surfaces exposed to the outside world or gastrointestinal tract (

) or internal cavities (

endothelium The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...

) come in numerous shapes and forms – from single layers of flat cells, to cells with small beating hair-like

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

in the lungs, to column-like cells that line the

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

. Endothelial cells are cells that line internal cavities including blood vessels and glands. Lining cells regulate what can and can't pass through them, protect internal structures, and function as sensory surfaces.

Organs

Organs In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a f ...

, structured collections of cells with a specific function, mostly sit within the body, with the exception of

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

. Examples include the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

s and

liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

. Many organs reside within

cavities Cavity may refer to: Biology and healthcare *Body cavity, a fluid-filled space in many animals where organs typically develop **Gastrovascular cavity, the primary organ of digestion and circulation in cnidarians and flatworms *Dental cavity or too ...

within the body. These cavities include the

(which contains the stomach, for example) and

pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls. The inner pleura, called the visceral pleura, covers the surface of each lung and dips b ...

, which contains the lungs.

Heart

The heart is an organ located in the

thoracic cavity The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...

between the

s and slightly to the left. It is surrounded by the

pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made of ...

which holds it in place in the

mediastinum The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esophagu ...

and serves to protect it from blunt trauma,

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

and help lubricate the movement of the heart via

pericardial fluid Pericardial fluid is the serous fluid secreted by the serous layer of the pericardium into the pericardial cavity. The pericardium consists of two layers, an outer fibrous layer and the inner serous layer. This serous layer has two membranes which ...

. The heart works by pumping blood around the body allowing

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

waste Waste (or wastes) are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor economic value. A waste prod ...

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

s and

white blood cell White blood cells, also called leukocytes or leucocytes, are the cell (biology), cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and de ...

s to be transported. Diagram of the human heart (cropped)

The heart is composed of two atrium and two ventricles. The primary purpose of the atrium is to allow uninterrupted venous blood flow to the heart during

ventricular systole The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following ...

. This allows enough blood to get into the ventricles during

atrial systole The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following ...

. A lack of the atrium would cause a decrease in cardiac output of 75%. The purpose of the ventricles is to pump blood to the lungs through the right ventricle and to the rest of the body through the left ventricle. The heart has an electrical conduction system to control the contractions and relaxation of the muscle. It starts in the

sinoatrial node The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximat ...

traveling through the atria causing them to pump blood into the ventricles. It then travels to the

atrioventricular node The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the lower back section of t ...

which makes the signal slow down slightly allowing the ventricles to fill with blood before pumping it out and starting the cycle over again.

Coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...

is the leading cause of death worldwide, making up 16% of all deaths. It is caused by the buildup of

plaque Plaque may refer to: Commemorations or awards * Commemorative plaque, a plate or tablet fixed to a wall to mark an event, person, etc. * Memorial Plaque (medallion), issued to next-of-kin of dead British military personnel after World War I * Pla ...

in the

coronary arteries The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ of ...

supplying the heart, eventually the arteries may become so narrow that not enough blood is able to reach the

myocardium Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that ...

, a condition known as myocardial infarction or heart attack, this can cause

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possib ...

and eventually death. Risk factors for coronary artery disease include

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's we ...

smoking Smoking is a practice in which a substance is burned and the resulting smoke is typically breathed in to be tasted and absorbed into the bloodstream. Most commonly, the substance used is the dried leaves of the tobacco plant, which have bee ...

high cholesterol Hypercholesterolemia, also called high cholesterol, is the presence of high levels of cholesterol in the blood. It is a form of hyperlipidemia (high levels of lipids in the blood), hyperlipoproteinemia (high levels of lipoproteins in the blood), ...

high blood pressure Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

lack of exercise Sedentary lifestyle is a lifestyle type, in which one is physically inactive and does little or no physical movement and or exercise. A person living a sedentary lifestyle is often sitting or lying down while engaged in an activity like socia ...

and

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

. Cancer can affect the heart, though it is exceedingly rare and has usually

metastasized Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...

from another part of the body such as the

lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...

breasts The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues. In females, it serves as the mammary gland, which produces and secret ...

. This is because the heart cells quickly stop dividing and all growth occurs through size increase rather than

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

Gallbladder

The gallbladder is a hollow pear shaped organ located posterior to the inferior middle part of the right lobe of the liver. It is variable in shape and size. It stores

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile ...

before it is released into the small intestine via the

common bile duct The common bile duct, sometimes abbreviated as CBD, is a duct in the gastrointestinal tract of organisms that have a gallbladder. It is formed by the confluence of the common hepatic duct and cystic duct and terminates by uniting with pancreati ...

to help with digestion of fats. It receives bile from the

via the

cystic duct The cystic duct is the short duct that joins the gallbladder to the common hepatic duct. It usually lies next to the cystic artery. It is of variable length. It contains 'spiral valves of Heister', which do not provide much resistance to the ...

which connects to the

common hepatic duct The common hepatic duct is the first part of the biliary tract. It joins the cystic duct coming from the gallbladder to form the common bile duct. Structure The common hepatic duct is the first part of the biliary tract. It is formed by the ...

to form the

. The gallbladder gets its blood supply from the

cystic artery The cystic artery (also known as bachelor artery) supplies oxygenated blood to the gallbladder and cystic duct. Most common arrangement In the classic arrangement, occurring with a frequency of approximately 70%, a singular cystic artery originat ...

which in most people emerges from the

right hepatic artery The hepatic artery proper (also proper hepatic artery) is the artery that supplies the liver and gallbladder. It raises from the common hepatic artery, a branch of the celiac artery. Structure The hepatic artery proper arises from the common h ...

Gallstone A gallstone is a calculus (medicine), stone formed within the gallbladder from precipitated bile components. The term cholelithiasis may refer to the presence of gallstones or to any disease caused by gallstones, and choledocholithiasis refers to ...

s is a common disease in which one or more stones form in the gallbladder or biliary tract. Most people are asymptomatic but if a stone blocks the biliary tract it causes a gallbladder attack, symptoms may include sudden pain in the upper right abdomen and or center of the abdomen. Nausea and vomiting may also occur. Typical treatment is removal of the gallbladder through a procedure called a

cholecystectomy Cholecystectomy is the surgical removal of the gallbladder. Cholecystectomy is a common treatment of symptomatic gallstones and other gallbladder conditions. In 2011, cholecystectomy was the eighth most common operating room procedure performed i ...

. Having gallstones is a risk factor for

gallbladder cancer Gallbladder cancer is a relatively uncommon cancer, with an incidence of fewer than 2 cases per 100,000 people per year in the United States. It is particularly common in central and South America, central and eastern Europe, Japan and northern In ...

which although quite uncommon is rapidly fatal if not diagnosed early.

Systems

Circulatory system

The

circulatory system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

consists of the

and

blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...

s (

arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

s and

capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

). The heart propels the circulation of the blood, which serves as a "transportation system" to transfer

, fuel, nutrients, waste products, immune cells and signalling molecules (i.e.

hormones A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...

) from one part of the body to another. Paths of blood circulation within the human body can be divided into two circuits: the

pulmonary circuit The pulmonary circulation is a division of the circulatory system in all vertebrates. The circuit begins with deoxygenated blood returned from the body to the right atrium of the heart where it is pumped out from the right ventricle to the lungs ...

, which pumps blood to the lungs to receive

and leave

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

, and the systemic circuit, which carries blood from the heart off to the rest of the body. The blood consists of fluid that carries cells in the circulation, including some that move from tissue to blood vessels and back, as well as the

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

and

bone marrow Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...

Digestive system

The

digestive system The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...

consists of the mouth including the

tongue The tongue is a muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper surfa ...

and

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

, (

small Small may refer to: Science and technology * SMALL, an ALGOL-like programming language * Small (anatomy), the lumbar region of the back * ''Small'' (journal), a nano-science publication * <small>, an HTML element that defines smaller text ...

and

large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being r ...

s, and

rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the Gastrointestinal tract, gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the s ...

), as well as the

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...

, and

salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary gla ...

s. It converts food into small, nutritional, non-toxic

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

s for distribution and absorption into the body. These molecules take the form of

s (which are broken down into

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s),

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...

vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an Nutrient#Essential nutrients, essential micronutrient that an organism needs in small quantities for the proper functioning of its ...

s and

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

s (the last of which are mainly ionic rather than molecular). After being

swallowed Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing ...

, food moves through the

by means of

peristalsis Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, which ...

: the systematic expansion and contraction of muscles to push food from one area to the next. Digestion begins in the

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

, which chews food into smaller pieces for easier digestion. Then it is

, and moves through the

to the

. In the stomach, food is mixed with

gastric acid Gastric acid, gastric juice, or stomach acid is a digestive fluid formed within the stomach lining. With a pH between 1 and 3, gastric acid plays a key role in digestion of proteins by activating digestive enzymes, which together break down the ...

s to allow the extraction of

s. What is left is called

chyme Chyme or chymus (; from Greek χυμός ''khymos'', "juice") is the semi-fluid mass of partly digested food that is expelled by a person's stomach, through the pyloric valve, into the duodenum small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

, which absorbs the nutrients and water from the chyme. What remains passes on to the

, where it is dried to form

feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

; these are then stored in the

until they are expelled through the

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

Endocrine system

The

endocrine system The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the neu ...

consists of the principal

endocrine gland Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid ...

s: the

pituitary In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypop ...

thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thy ...

adrenal The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which ...

parathyroid Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods. Humans usually have four parathyroid glands, located on the back of the thyroid gland in variable locations. The parathyroid gland produces and secretes par ...

s, and

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...

s, but nearly all organs and tissues produce specific endocrine

s as well. The endocrine hormones serve as signals from one body system to another regarding an enormous array of conditions, and resulting in variety of changes of function.

Immune system

The

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

consists of the

s, the

thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

lymph node A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that inclu ...

s and

lymph Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to ...

channels, which are also part of the

lymphatic system The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...

. The immune system provides a mechanism for the body to distinguish its own cells and tissues from outside cells and substances and to neutralize or destroy the latter by using specialized proteins such as

antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

cytokines Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

, and

toll-like receptors Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane-spanning receptors usually expressed on sentinel cells such as macrophages and dendritic cells, that recognize s ...

, among many others. Skin layers

Integumentary system

The

integumentary system The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the skin and its appendages, which act as a physical barrier between the external environment and the internal environment that it serves ...

consists of the covering of the body (the skin), including hair and nails as well as other functionally important structures such as the

sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin that produce sweat. Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial sur ...

s and

sebaceous gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...

s. The skin provides containment, structure, and protection for other organs, and serves as a major sensory interface with the outside world.

Lymphatic system

The

extracts, transports and metabolizes lymph, the fluid found in between cells. The lymphatic system is similar to the circulatory system in terms of both its structure and its most basic function, to carry a body fluid.

Musculoskeletal system

The

musculoskeletal system The human musculoskeletal system (also known as the human locomotor system, and previously the activity system) is an organ system that gives humans the ability to move using their muscular and skeletal systems. The musculoskeletal system provid ...

consists of the human skeleton (which includes

bone A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...

ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal li ...

tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...

joints A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

and

cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...

) and attached

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s. It gives the body basic structure and the ability for movement. In addition to their structural role, the larger bones in the body contain

, the site of production of blood cells. Also, all bones are major storage sites for

and

. This system can be split up into the

muscular system The muscular system is an organ (anatomy), organ system consisting of skeletal muscle, skeletal, smooth muscle, smooth, and cardiac muscle, cardiac muscle. It permits movement of the body, maintains posture, and circulates blood throughout the bo ...

and the

skeletal system A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

Nervous system

The

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...

consists of the body's

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s and

glia Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form myel ...

l cells, which together form the

nerves A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympatheti ...

and

gray matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distingui ...

which in turn form the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

and related structures. The brain is the organ of

thought In their most common sense, the terms thought and thinking refer to conscious cognitive processes that can happen independently of sensory stimulation. Their most paradigmatic forms are judging, reasoning, concept formation, problem solving, a ...

, emotion,

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...

, and

sensory processing Sensory processing is the process that organizes sensation from one's own body and the environment, thus making it possible to use the body effectively within the environment. Specifically, it deals with how the brain processes multiple sensory mod ...

; it serves many aspects of communication and controls various systems and functions. The

special senses In medicine and anatomy, the special senses are the senses that have specialized organs devoted to them: * vision (the eye) * hearing and balance (the ear, which includes the auditory system and vestibular system) * smell (the nose) * ta ...

consist of

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain un ...

hearing Hearing, or auditory perception, is the ability to perceive sounds In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psycholog ...

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...

, and smell. The

eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conve ...

ear An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of ...

, and nose gather information about the body's environment. From a structural perspective, the

is typically subdivided into two component parts: the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

(CNS), composed of the brain and the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

; and the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain ...

(PNS), composed of the nerves and

outside the brain and spinal cord. The CNS is mostly responsible for organizing

motion In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and mea ...

, processing

sensory information A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system re ...

, thought, memory,

cognition Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...

and other such functions.Kim Ann Zimmermann
"Nervous System: Facts, Function & Diseases"
''Live Science'', Accessed 1 July 2019. It remains a matter of some debate whether the CNS directly gives rise to

consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...

. The

(PNS) is mostly responsible for gathering information with

sensory neuron Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The cell ...

s and directing body movements with

motor neuron A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectl ...

s. From a functional perspective, the nervous system is again typically divided into two component parts: the

somatic nervous system The somatic nervous system (SNS), or voluntary nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The somatic nervous system consists of sensory nerves carryi ...

(SNS) and the

autonomic nervous system The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies viscera, internal organs, smooth muscle and glands. The autonomic nervous system is a control ...

(ANS). The SNS is involved in voluntary functions like

speaking Speech is a human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if they are th ...

and sensory processes. The ANS is involved in involuntary processes, such as

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...

and regulating

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...

. The nervous system is subject to many different diseases. In

epilepsy Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...

, abnormal electrical activity in the brain can cause

seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or neural oscillation, synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much o ...

. In

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...

, the

attacks the nerve linings, damaging the nerves' ability to transmit signals.

Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...

(ALS), also known as

Lou Gehrig Henry Louis Gehrig (born Heinrich Ludwig Gehrig ; June 19, 1903June 2, 1941) was an American professional baseball first baseman who played 17 seasons in Major League Baseball (MLB) for the New York Yankees (1923–1939). Gehrig was renowned f ...

's disease, is a

disease which gradually reduces movement in patients. There are also many other diseases of the nervous system.

Reproductive system

The primary purpose of the reproductive system is to produce new humans in the form of

child A child ( : children) is a human being between the stages of birth and puberty, or between the developmental period of infancy and puberty. The legal definition of ''child'' generally refers to a minor, otherwise known as a person younger ...

ren and ensure their

sexual development Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. I ...

so that they can produce new humans too. It is composed of the

s (

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...

and

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

) which produce

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

and

sperm cells A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, ...

(

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s) and produce

necessary for proper

. The rest of the

gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). Structure De ...

s and ducts of the reproductive system are responsible for the transportation and sustaining of the

s and to nurture the offspring. The reproductive system is first stimulated by the

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...

during

puberty Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. ...

which causes the

and

to produce

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...

(male) and

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

and

progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the m ...

(female). Male puberty generally occurs between the ages of 13-15 and is characterized by beginning of

sperm production Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules ...

and the development of

secondary sex characteristic Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These characteristics are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a sp ...

s such as increased height and weight, broadened shoulders,

pubic In vertebrates, the pubic region ( la, pubis) is the most forward-facing (ventral and anterior) of the three main regions making up the coxal bone. The left and right pubic regions are each made up of three sections, a superior ramus, inferior r ...

and

facial hair Facial hair is hair grown on the face, usually on the chin, cheeks, and upper lip region. It is typically a secondary sex characteristic of human males. Men typically start developing facial hair in the later stages of puberty or adolescence, ...

, voice deepening and muscle development. Female puberty generally occurs between the ages of 9-13 and is characterized by

ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilized ...

and

menstruation Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The menstrual cycle is characterized by the rise and fall of hor ...

. The growth of secondary sex characteristics such as growth of

and

underarm hair Underarm hair, also known as axillary hair, is the hair in the underarm area (''axilla''). Development Underarm or axillary hair goes through four stages of development, driven by weak androgens produced by the adrenal in males and females du ...

breast The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues. In females, it serves as the mammary gland, which produces and secret ...

uterine The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

and

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

l growth, widening hips and increased height and weight also occur during the female puberty process. Human male reproductive system en

The external

male reproductive system The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body and within the pelvis. The main male sex organs are the penis and the tes ...

is made up of the

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do n ...

and the

scrotum The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum cont ...

which is a bag that protects the

testis A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testostero ...

. The penis consists of the

glans The glans (, plural "glandes" ; from the Latin word for "acorn") is a vascular structure located at the tip of the penis in male mammals or a homologous genital structure of the clitoris in female mammals. Structure The exterior structure ...

which is the head of the penis and contains the

urethra The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra con ...

and

urinary meatus The urinary meatus, (, ) also known as the external urethral orifice, is the opening of the urethra. It is the point where urine exits the urethra in both sexes and where semen exits the urethra in males. The meatus has varying degrees of sensiti ...

the point where urine exits the penis, the rest of the penis is called the shaft or corpus cavernosum and contains most of the

. The glans is covered by a fold of skin called the

foreskin In male human anatomy, the foreskin, also known as the prepuce, is the double-layered fold of skin, mucosal and muscular tissue at the distal end of the human penis that covers the glans and the urinary meatus. The foreskin is attached to the g ...

though this can be removed through

circumcision Circumcision is a surgical procedure, procedure that removes the foreskin from the human penis. In the most common form of the operation, the foreskin is extended with forceps, then a circumcision device may be placed, after which the foreskin ...

Mons-pubis-anatomical-location-in-female-reproductive-system

Internally the male reproductive system starts in the testes where hundreds of

seminiferous tubule Seminiferous tubules are located within the testes, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa. Structure The epithelium of the tubule consists of a type of sustentacular cells known ...

s produce

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

which is then stored and matured into

spermatozoon A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, t ...

in the

epididymis The epididymis (; plural: epididymides or ) is a tube that connects a testicle to a vas deferens in the male reproductive system. It is a single, narrow, tightly-coiled tube in adult humans, in length. It serves as an interconnection between the ...

. They are then brought through the

vas deferens The vas deferens or ductus deferens is part of the male reproductive system of many vertebrates. The ducts transport sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation. The vas deferens is a partially coiled tube ...

which leads away from the testes to the

seminal vesicles The seminal vesicles (also called vesicular glands, or seminal glands) are a pair of two convoluted tubular glands that lie behind the urinary bladder of some male mammals. They secrete fluid that partly composes the semen. The vesicles are 5� ...

where the sperm cells are mixed with a

fructose Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...

-rich fluid from the seminal vesicles allowing the sperm to stay alive and remain healthy. It is then brought by the

ejaculatory duct The ejaculatory ducts (''ductus ejaculatorii'') are paired structures in male anatomy. Each ejaculatory duct is formed by the union of the vas deferens with the duct of the seminal vesicle. They pass through the prostate, and open into the ureth ...

through the

prostate The prostate is both an Male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, ...

and

bulbourethral gland The bulbourethral glands or Cowper's glands (named for English anatomist William Cowper) are two small exocrine glands in the reproductive system of many male mammals (of all domesticated animals, they are absent only in dogs). They are homolog ...

, and mixed with fluids from said glands. The fluid from the prostate helps to neutralize the acidity of the vagina and keep the sperm alive. This mixture of sperm and accessory gland fluids is called

semen Semen, also known as seminal fluid, is an organic bodily fluid created to contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. Semen i ...

and is released through the

during

ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential componen ...

. Almost the entire internal male reproductive system works in pairs with two

, two

s, two

s, but only one

and

. The external

female reproductive system The female reproductive system is made up of the internal and external sex organs that function in the reproduction of new offspring. In humans, the female reproductive system is immature at birth and develops to maturity at puberty to be ...

also called the

vulva The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external sex organ, female sex organs. The vulva includes the mons pubis (or mons veneris), labia majora, labia minora, clitoris, bulb of vestibu ...

consists of the

mons pubis In human anatomy, and in mammals in general, the ''mons pubis'' or pubic mound (also known simply as the mons, and known specifically in females as the ''mons Venus'' or ''mons veneris'') is a rounded mass of fatty tissue found over the pubic symp ...

a fatty mass that covers the pubis, the

labia majora The labia majora (singular: ''labium majus'') are two prominent longitudinal cutaneous folds that extend downward and backward from the mons pubis to the perineum. Together with the labia minora they form the labia of the vulva. The labia majo ...

(outer lips of the vagina), the

labia minora The labia minora (Latin for 'smaller lips', singular: ''labium minus'', 'smaller lip'), also known as the inner labia, inner lips, vaginal lips or nymphae are two flaps of skin on either side of the human vaginal opening in the vulva, situated be ...

(inner lips of the vagina), the

vaginal opening In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

which opens into vagina and is where the penis is inserted during

sexual intercourse Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...

and children are born, the urethral opening which is the opening for the

that carries

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...

from the

bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

and the

clitoris The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the ope ...

which contains the most sensitive nerve endings and in humans has no use other than

sexual pleasure Sexual stimulation is any stimulus (including bodily contact) that leads to, enhances and maintains sexual arousal, and may lead to orgasm. Although sexual arousal may arise without physical stimulation, achieving orgasm usually requires physica ...

. Located between the anus and vagina is the

perineum The perineum in humans is the space between the anus and scrotum in the male, or between the anus and the vulva in the female. The perineum is the region of the body between the pubic symphysis (pubic arch) and the coccyx (tail bone), includi ...

Internally the female reproductive system contains two

, the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

, two

fallopian tube The fallopian tubes, also known as uterine tubes, oviducts or salpinges (singular salpinx), are paired tubes in the human female that stretch from the uterus to the ovaries. The fallopian tubes are part of the female reproductive system. In ot ...

s and the

cervix The cervix or cervix uteri (Latin, 'neck of the uterus') is the lower part of the uterus (womb) in the human female reproductive system. The cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape, which changes during ...

. At birth a female has about 700,000

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

s (the immature version of the egg cell) in both ovaries combined, though this degenerates to about 400,000 by the time

is reached. This is a lifetime supply as after birth no more

s are produced, compared to males where

are produced during their entire lifetime. During puberty the

menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that make pregnancy possible. The ovarian cycle controls the production and release of eggs a ...

begins for the first time, in response to low

and

levels the

releases

gonadotropin releasing hormone Gonadotropin-releasing hormone (GnRH) is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and released ...

(GnRH). This causes the

anterior pituitary gland A major organ of the endocrine system, the anterior pituitary (also called the adenohypophysis or pars anterior) is the glandular, anterior lobe that together with the posterior lobe (posterior pituitary, or the neurohypophysis) makes up the p ...

to release

follicle-stimulating hormone Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, pubertal maturation, an ...

(FSH) and

luteinizing hormone Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) ...

(LH). FSH stimulates

ovarian follicle An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. At the time of puberty, women have approximately 200,000 to 300,000 follicles, each with th ...

s to grow and one dominant follicle will eventually take over. As it continues to grow it releases more and more

estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development of f ...

which stimulates LH secretion and suppresses FSH secretion preventing further follicular growth. When LH levels are highest the follicle ruptures releasing the

ovum The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is ...

in a process called

where it is then moved to one of the

s. After ovulation the portion of the follicle that remains in the ovary is transformed into corpus luteum which continues to produce estrogen and high levels of progesterone. The

causes the

endometrium The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The functional laye ...

to grow thick preparing it for implantation of a

fertilized egg A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

. If fertilization occurs the corpus luteum continues to secrete hormones until the

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...

develops enough to secrete the necessary hormones for maintaining

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

. Eventually the corpus luteum will turn into

corpus albicans The corpus albicans (Latin for "whitening body"; also known as atretic corpus luteum, corpus candicans, or simply as albicans) is the regressed form of the corpus luteum. As the corpus luteum is being broken down by macrophages, fibroblasts lay d ...

which is essentially scar tissue. If fertilization fails the corpus luteum will degrade into

and stop secreting enough

and

causing the endometrial lining to break resulting in

. Many diseases affect the reproductive system such as

polycystic ovary syndrome Polycystic ovary syndrome, or PCOS, is the most common endocrine disorder in women of reproductive age. The syndrome is named after the characteristic cysts which may form on the ovaries, though it is important to note that this is a sign and no ...

(PCOS) which is characterized by elevated androgen levels,

menstrual irregularities Irregular menstruation is a menstrual disorder whose manifestations include irregular cycle lengths as well as metrorrhagia (vaginal bleeding between expected periods). The possible causes of irregular menstruation may vary. The common factors of ...

and/or small

cysts A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...

on one or both of the ovaries. It is a common disease affecting at least 7% of adult women. Symptoms include excess body hair,

infertility Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal state ...

weight gain Weight gain is an increase in body weight. This can involve an increase in muscle mass, fat deposits, excess fluids such as water or other factors. Weight gain can be a symptom of a serious medical condition. Description Weight gain occurs wh ...

male pattern baldness Pattern hair loss (also known as androgenetic alopecia (AGA)) is a hair loss condition that primarily affects the top and front of the scalp. In male-pattern hair loss (MPHL), the hair loss typically presents itself as either a receding front ha ...

and

irregular menstruation Irregular menstruation is a menstrual disorder whose manifestations include irregular cycle lengths as well as metrorrhagia (vaginal bleeding between expected periods). The possible causes of irregular menstruation may vary. The common factors of ...

. Another reproductive disease is

testicular torsion Testicular torsion occurs when the spermatic cord (from which the testicle is suspended) twists, cutting off the blood supply to the testicle. The most common symptom in children is sudden, severe testicular pain. The testicle may be higher than ...

, it occurs when the

spermatic cord The spermatic cord is the cord-like structure in males formed by the vas deferens (''ductus deferens'') and surrounding tissue that runs from the deep inguinal ring down to each testicle. Its serosal covering, the tunica vaginalis, is an exten ...

which holds up the testicle wraps around itself cutting off blood flow to the testicle.

Testicular torsion Testicular torsion occurs when the spermatic cord (from which the testicle is suspended) twists, cutting off the blood supply to the testicle. The most common symptom in children is sudden, severe testicular pain. The testicle may be higher than ...

is a

medical emergency A medical emergency is an acute injury or illness that poses an immediate risk to a person's life or long-term health, sometimes referred to as a situation risking "life or limb". These emergencies may require assistance from another, qualified p ...

and can result in testicular death or

if not treated immediately by physically unwrapping the

. If the testicle has suffered severe damage, it may need to be surgically in a lateral

orchiectomy Orchiectomy (also named orchidectomy, and sometimes shortened as orchi or orchie) is a surgical procedure in which one or both testicles are removed. The surgery is performed as treatment for testicular cancer, as part of surgery for transgend ...

. The primary symptom of testicular torsion is severe

testicular pain Testicular pain, also known as scrotal pain, occurs when part or all of either one or both testicles hurt. Pain in the scrotum is also often included. Testicular pain may be of sudden onset or of long duration. Causes range from non serious musc ...

at rest, nausea and vomiting may also occur. Testicular torsion can occur at any age though it is most common in 12-18 year olds.

Sexually transmitted infection Sexually transmitted infections (STIs), also referred to as sexually transmitted diseases (STDs) and the older term venereal diseases, are infections that are Transmission (medicine), spread by Human sexual activity, sexual activity, especi ...

s such as

syphilis Syphilis () is a sexually transmitted infection caused by the bacterium ''Treponema pallidum'' subspecies ''pallidum''. The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, an ...

HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...

chlamydia Chlamydia, or more specifically a chlamydia infection, is a sexually transmitted infection caused by the bacterium ''Chlamydia trachomatis''. Most people who are infected have no symptoms. When symptoms do appear they may occur only several wee ...

HPV Human papillomavirus infection (HPV infection) is caused by a DNA virus from the '' Papillomaviridae'' family. Many HPV infections cause no symptoms and 90% resolve spontaneously within two years. In some cases, an HPV infection persists and re ...

and

genital wart Genital warts are a sexually transmitted infection caused by certain types of human papillomavirus (HPV). They are generally pink in color and project out from the surface of the skin. Usually they cause few symptoms, but can occasionally be pai ...

s are spread through

including

oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or or ...

, vaginal and

anal sex Anal sex or anal intercourse is generally the insertion and thrusting of the erect penis into a person's anus, or anus and rectum, for sexual pleasure.Sepages 270–271for anal sex information, anpage 118for information about the clitoris. ...

. Many of these infections can be lethal if left untreated though others are mostly harmless. Cancer can affect many parts of the reproductive system including the penis,

testicles A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testostero ...

, fallopian,

and

Respiratory system

The

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

consists of the nose,

nasopharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...

trachea The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...

, and

. It brings oxygen from the air and excretes

and water back into the air. First,

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

is pulled through the trachea into the lungs by the diaphragm pushing down, which creates a

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...

. Air is briefly stored inside small sacs known as

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * ...

(sing.: alveolus) before being expelled from the lungs when the diaphragm contracts again. Each alveolus is surrounded by

carrying deoxygenated blood, which absorbs oxygen out of the air and into the

bloodstream The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

."How the Lungs and Respiratory System Work"
'' Web MD'', Accessed 30 June 2019. For the respiratory system to function properly, there need to be as few impediments as possible to the movement of air within the lungs.

Inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

of the lungs and excess

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

are common sources of breathing difficulties. In

asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, cou ...

, the respiratory system is persistently inflamed, causing

wheezing A wheeze is a continuous, coarse, whistling sound produced in the respiratory airways during breathing. For wheezes to occur, some part of the respiratory tree must be narrowed or obstructed (for example narrowing of the lower respiratory tract ...

and/or

shortness of breath Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing disc ...

Pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...

occurs through

of the alveoli, and may be caused by

tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...

Emphysema Emphysema, or pulmonary emphysema, is a lower respiratory tract disease, characterised by air-filled spaces ( pneumatoses) in the lungs, that can vary in size and may be very large. The spaces are caused by the breakdown of the walls of the alve ...

, commonly a result of

, is caused by damage to connections between the alveoli.

Urinary system

The

urinary system The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, urinary bladder, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and bl ...

consists of the two

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...

s, two

ureter The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...

, and

. It removes waste materials from the blood through urine, which carries a variety of waste molecules and excess

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s and water out of the body. First, the

s filter the blood through their respective

nephron The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ca ...

s, removing

waste products Waste (or wastes) are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor Value (economics), economic v ...

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...

creatinine Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass). Biological relevance Serum creatinine (a blood measurement) is an import ...

and maintaining the proper balance of

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...

s and turning the waste products into

by combining them with water from the blood. The kidneys filter about 150 quarts (170 liters) of blood daily, but most of it is returned to the blood stream with only 1-2 quarts (1-2 liters) ending up as urine. The urine is brought by the

s from the kidneys down to the

. The

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

lining the ureter walls continuously tighten and relax through a process called

to force urine away from the kidneys and down into the bladder. Small amounts of urine are released into the bladder every 10–15 seconds. The bladder is a hollow balloon shaped organ located in the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

. It stores urine until the brain signals it to relax the

urinary sphincter The urethral sphincters are two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are either the male or female external urethral sphincter and the internal urethral sphincter. When either of t ...

and release the urine into the urethra starting

urination Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...

. A normal bladder can hold up to 16 ounces (half a liter) for 3–5 hours comfortably. Numerous diseases affect the urinary system including

kidney stones Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...

which are formed when materials in the urine concentrate enough to form a solid mass,

urinary tract infection A urinary tract infection (UTI) is an infection that affects part of the urinary tract. When it affects the lower urinary tract it is known as a bladder infection (cystitis) and when it affects the upper urinary tract it is known as a kidney ...

s which are infections of the urinary tract and can cause pain when urinating, frequent urination and even death if left untreated.

Renal failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...

occurs when the kidneys fail to adequately filter waste from the blood and can lead to death if not treated with dialysis or kidney transplantation.

Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

can affect the

kidneys The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...

and

ureters The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...

with the latter two being far more rare.

Anatomy

Human

is the study of the shape and form of the human body. The human body has four limbs (two arms and two legs), a head and a

which connect to the

torso The torso or trunk is an anatomical term for the central part, or the core, of the body of many animals (including humans), from which the head, neck, limbs, tail and other appendages extend. The tetrapod torso — including that of a human � ...

. The body's shape is determined by a strong

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

made of

and

, surrounded by fat (

adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...

), muscle,

, organs, and other structures. The spine at the back of the skeleton contains the flexible

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...

which surrounds the

, which is a collection of nerve fibres connecting the

to the rest of the body.

Nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

s connect the spinal cord and brain to the rest of the body. All major bones, muscles, and nerves in the body are named, with the exception of

anatomical variation An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categ ...

s such as

sesamoid bone In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for ' sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be pres ...

s and

accessory muscle An accessory muscle is a relatively rare anatomical variation where duplication of a muscle may appear anywhere in the muscular system. Treatment is not indicated unless the accessory muscle interferes with normal function. Examples are the sterna ...

s. Blood vessels carry blood throughout the body, which moves because of the beating of the

Venule A venule is a very small blood vessel in the microcirculation that allows blood to return from the capillary beds to drain into the larger blood vessels, the veins. Venules range from 7μm to 1mm in diameter. Veins contain approximately 70% of t ...

s and

s collect blood low in oxygen from tissues throughout the body. These collect in progressively larger veins until they reach the body's two largest veins, the superior and

inferior vena cava The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...

, which drain blood into the right side of the heart. From here, the blood is pumped into the

s where it receives oxygen and drains back into the left side of the heart. From here, it is pumped into the body's largest

artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...

, the

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...

, and then progressively smaller arteries and

arteriole An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. Arterioles have muscular walls (usually only one to two layers of smooth muscle cells) and are the primar ...

s until it reaches tissue. Here blood passes from small arteries into

, then small veins and the process begins again. Blood carries

, waste products, and

s from one place in the body to another. Blood is filtered at the

s and

. The body consists of a number of

body cavities A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, and ...

, separated areas which house different organ systems. The brain and

reside in an area protected from the rest of the body by the

blood brain barrier Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the Cell (biology), cells, and transports Metabolic waste, metabolic waste products away from th ...

. The lungs sit in the

pleural cavity The pleural cavity, pleural space, or interpleural space is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable lubrication bet ...

. The

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...

, and

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

sit in the

abdominal cavity The abdominal cavity is a large body cavity in humans and many other animals that contains many organs. It is a part of the abdominopelvic cavity. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the th ...

. Height, weight,

shape A shape or figure is a graphics, graphical representation of an object or its external boundary, outline, or external Surface (mathematics), surface, as opposed to other properties such as color, Surface texture, texture, or material type. A pl ...

and other

body proportions While there is significant variation in anatomical proportions between people, certain body proportions have become canonical in figurative art. The study of body proportions, as part of the study of artistic anatomy, explores the relation of t ...

vary individually and with age and sex. Body shape is influenced by the distribution of bones,

and

fat tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular en ...

Physiology

Human

is the study of how the human body functions. This includes the mechanical, physical, bioelectrical, and

biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology an ...

functions of humans in good health, from

to the cells of which they are composed. The human body consists of many interacting systems of organs. These interact to maintain

, keeping the body in a stable state with safe levels of substances such as sugar and oxygen in the blood. Each system contributes to homeostasis, of itself, other systems, and the entire body. Some combined systems are referred to by joint names. For example, the nervous system and the endocrine system operate together as the

neuroendocrine system Neuroendocrinology is the branch of biology (specifically of physiology) which studies the interaction between the nervous system and the endocrine system; i.e. how the brain regulates the hormonal activity in the body. The nervous and endocrine ...

. The nervous system receives information from the body, and transmits this to the brain via

nerve impulse An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, c ...

s and

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neuro ...

s. At the same time, the

releases hormones, such as to help regulate

and volume. Together, these systems regulate the internal environment of the body, maintaining blood flow, posture, energy supply, temperature, and acid balance ( pH).

Development

Development of the human body is the process of growth to maturity. The process begins with fertilisation, where an egg released from the

ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...

of a female is penetrated by

. The egg then lodges in the

, where an

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

and later

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...

develop until

birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...

. Growth and development occur after birth, and include both physical and psychological development, influenced by genetic, hormonal, environmental and other factors. Development and growth continue throughout life, through

childhood A child (plural, : children) is a human being between the stages of childbirth, birth and puberty, or between the Development of the human body, developmental period of infancy and puberty. The legal definition of ''child'' generally refers ...

adolescence Adolescence () is a transitional stage of physical and psychological development that generally occurs during the period from puberty to adulthood (typically corresponding to the age of majority). Adolescence is usually associated with the t ...

, and through

adulthood An adult is a human or other animal that has reached full growth. In human context, the term ''adult'' has meanings associated with social and legal concepts. In contrast to a " minor", a legal adult is a person who has attained the age of major ...

old age Old age refers to ages nearing or surpassing the life expectancy of human beings, and is thus the end of the human life cycle. Terms and euphemisms for people at this age include old people, the elderly (worldwide usage), OAPs (British usage ...

, and are referred to as the process of

aging Ageing ( BE) or aging ( AE) is the process of becoming older. The term refers mainly to humans, many other animals, and fungi, whereas for example, bacteria, perennial plants and some simple animals are potentially biologically immortal. In ...

Society and culture

Professional study

Anatomical Male Figure Showing Heart, Lungs, and Main Arteries

Health professional A health professional, healthcare professional, or healthcare worker (sometimes abbreviated HCW) is a provider of health care treatment and advice based on formal training and experience. The field includes those who work as a nurse, physician (suc ...

s learn about the human body from illustrations, models, and demonstrations. Medical and dental students in addition gain practical experience, for example by

dissection Dissection (from Latin ' "to cut to pieces"; also called anatomization) is the dismembering of the body of a deceased animal or plant to study its anatomical structure. Autopsy is used in pathology and forensic medicine to determine the cause o ...

of cadavers. Human anatomy,

, and

biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...

are basic medical sciences, generally taught to medical students in their first year at medical school.

Depiction

Anatomy has served the visual arts since Ancient Greek times, when the 5th century BC sculptor

Polykleitos Polykleitos ( grc, Πολύκλειτος) was an ancient Greek sculptor in bronze of the 5th century BCE. Alongside the Athenian sculptors Pheidias, Myron and Praxiteles, he is considered one of the most important sculptors of classical antiqu ...

wrote his ''Canon'' on the ideal proportions of the male nude. In the

Italian Renaissance The Italian Renaissance ( it, Rinascimento ) was a period in Italian history covering the 15th and 16th centuries. The period is known for the initial development of the broader Renaissance culture that spread across Europe and marked the trans ...

, artists from

Piero della Francesca Piero della Francesca (, also , ; – 12 October 1492), originally named Piero di Benedetto, was an Italian painter of the Early Renaissance. To contemporaries he was also known as a mathematician and geometer. Nowadays Piero della Francesca i ...

(c. 1415–1492) onwards, including

Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially res ...

(1452–1519) and his collaborator

Luca Pacioli Fra Luca Bartolomeo de Pacioli (sometimes ''Paccioli'' or ''Paciolo''; 1447 – 19 June 1517) was an Italian mathematician, Franciscan friar, collaborator with Leonardo da Vinci, and an early contributor to the field now known as accounting ...

(c. 1447–1517), learnt and wrote about the rules of art, including visual perspective and the proportions of the human body.

History of anatomy

Externarvm hvmani corporis sedivm partivmve, 1543

Ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...

, the ''

Hippocratic Corpus The Hippocratic Corpus (Latin: ''Corpus Hippocraticum''), or Hippocratic Collection, is a collection of around 60 early Ancient Greek medical works strongly associated with the physician Hippocrates and his teachings. The Hippocratic Corpus cove ...

'' described the anatomy of the skeleton and muscles. The 2nd century physician Galen of Pergamum compiled classical knowledge of anatomy into a text that was used throughout the Middle Ages. In the

Renaissance The Renaissance ( , ) , from , with the same meanings. is a period in European history marking the transition from the Middle Ages to modernity and covering the 15th and 16th centuries, characterized by an effort to revive and surpass ideas ...

Andreas Vesalius Andreas Vesalius (Latinized from Andries van Wezel) () was a 16th-century anatomist, physician, and author of one of the most influential books on human anatomy, ''De Humani Corporis Fabrica Libri Septem'' (''On the fabric of the human body'' '' ...

(1514–1564) pioneered the modern study of human anatomy by dissection, writing the influential book ''

De humani corporis fabrica ''De Humani Corporis Fabrica Libri Septem'' (Latin, lit. "On the fabric of the human body in seven books") is a set of books on human anatomy written by Andreas Vesalius (1514–1564) and published in 1543. It was a major advance in the history ...

''. Anatomy advanced further with the invention of the

and the study of the cellular structure of tissues and organs. Modern anatomy uses techniques such as

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

, computed tomography,

fluoroscopy Fluoroscopy () is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope () allows a physician to see the internal structure and functio ...

and

ultrasound imaging Medical ultrasound includes diagnostic techniques (mainly medical imaging, imaging techniques) using ultrasound, as well as therapeutic ultrasound, therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal ...

to study the body in unprecedented detail.

History of physiology

The study of human physiology began with

Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek physician of the classical period who is considered one of the most outstanding figures in the history of ...

in Ancient Greece, around 420 BCE, and with

Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...

(384–322 BCE) who applied critical thinking and emphasis on the relationship between structure and function.

Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...

(ca. 126–199) was the first to use experiments to probe the body's functions. The term physiology was introduced by the French physician

Jean Fernel Jean François Fernel ( Latinized as Ioannes Fernelius; 1497 – 26 April 1558) was a French physician who introduced the term "physiology" to describe the study of the body's function. He was the first person to describe the spinal canal. The l ...

(1497–1558). In the 17th century,

William Harvey William Harvey (1 April 1578 – 3 June 1657) was an English physician who made influential contributions in anatomy and physiology. He was the first known physician to describe completely, and in detail, the systemic circulation and proper ...

(1578–1657) described the

, pioneering the combination of close observation with careful experiment. In the 19th century, physiological knowledge began to accumulate at a rapid rate with the

cell theory In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of Cell (biology), cells, that they are the basic structural/organizational unit of all organisms, and that all cell ...

of Matthias Schleiden and

Theodor Schwann Theodor Schwann (; 7 December 181011 January 1882) was a German physician and physiologist. His most significant contribution to biology is considered to be the extension of cell theory to animals. Other contributions include the discovery of ...

in 1838, that organisms are made up of cells.

Claude Bernard Claude Bernard (; 12 July 1813 – 10 February 1878) was a French physiologist. Historian I. Bernard Cohen of Harvard University called Bernard "one of the greatest of all men of science". He originated the term '' milieu intérieur'', and the ...

(1813–1878) created the concept of the ''

milieu interieur The internal environment (or ''milieu intérieur'' in French language, French) was a concept developed by Claude Bernard, a French physiologist in the 19th century, to describe the Extracellular fluid#Interstitial fluid, interstitial fluid and it ...

'' (internal environment), which

Walter Cannon Walter Bradford Cannon (October 19, 1871 – October 1, 1945) was an American physiologist, professor and chairman of the Department of Physiology at Harvard Medical School. He coined the term "fight or flight response", and developed the theory ...

(1871–1945) later said was regulated to a steady state in

. In the 20th century, the physiologists

Knut Schmidt-Nielsen Knut Schmidt-Nielsen (September 24, 1915 – January 25, 2007) was a prominent figure in the field of comparative physiology and Professor of Physiology Emeritus at Duke University. Background Born in Trondheim, Norway. He was educated in Oslo and ...

and George Bartholomew extended their studies to

comparative physiology Comparative physiology is a List of academic disciplines, subdiscipline of physiology that studies and exploits the diversity of functional characteristics of various kinds of organisms. It is closely related to evolutionary physiology and environ ...

and

ecophysiology Ecophysiology (from Greek , ''oikos'', "house(hold)"; , ''physis'', "nature, origin"; and , '' -logia''), environmental physiology or physiological ecology is a biological discipline that studies the response of an organism's physiology to enviro ...

. Most recently,

evolutionary physiology Evolutionary physiology is the study of the biological evolution of physiological structures and processes; that is, the manner in which the functional characteristics of individuals in a population of organisms have responded to natural selectio ...

has become a distinct subdiscipline.

References

Books

* *

External links

*
The Book of Humans
' (from the late 18th and early 19th centuries)
Inner Body

Anatomia 1522–1867: Anatomical Plates from the Thomas Fisher Rare Book Library
{{DEFAULTSORT:Human Body

Composition

Cells

Genome

Tissues

Organs

Heart

Gallbladder

Systems

Circulatory system

Digestive system

Endocrine system

Immune system

Integumentary system

Lymphatic system

Musculoskeletal system

Nervous system

Reproductive system

Respiratory system

Urinary system

Anatomy

Physiology

Development

Society and culture

Professional study

Depiction

History of anatomy

History of physiology

See also

References

Books

External links