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The human body is the structure of a
human being Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human being
. It is composed of many different types of
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
that together create tissues and subsequently
organ systems An organ system is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertainment, and media * ''Network'' (1976 film), a 1976 American film * ''Network'' (2019 film), an Indian film * ...
. They ensure
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
and the
viability
viability
of the human body. It comprises a
head Head Sport GmbH is an American-Austrian manufacturing company Manufacturing is the creation or production Production may be: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in th ...

head
,
neck The neck is the part of the body on many vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

neck
, trunk (which includes the
thorax The thorax or chest is a part of the anatomy of humans, mammals, 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 Tagma (biology), divisions ...

thorax
and
abdomen The abdomen (colloquially called the belly, tummy, midriff 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 Trunk (anatomy) ...

abdomen
),
arm In human anatomy, the arm is the part of the upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and incl ...

arm
s and
hands A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

hands
,
legs A leg is a weight-bearing and animal locomotion, 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, ...
and
feet The foot (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemist ...

feet
. The study of the human body involves
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It ...

anatomy
,
physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
,
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

histology
and
embryology Embryology (from Ancient Greek, Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, ''-logy, -logia'') is the branch of biology that studies the Prenatal development (biology), prenatal development of gametes (sex cells), ...
. The body varies anatomically in known ways.
Physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
focuses on the systems and organs of the human body and their functions. Many systems and mechanisms interact in order to maintain
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
, with safe levels of substances such as sugar and oxygen in the blood. The body is studied by
health professional A health professional (or healthcare professional) may provide treatment and advice based on formal training and experience. The field includes those who work as a , (such as , , , , , etc), , , , , , , , , , , , , or who perform services in . A ...
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 (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
,
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
,
calcium Calcium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

calcium
and
phosphorus Phosphorus is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical el ...

phosphorus
. 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 H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...
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 Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
, 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 In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

sodium
and
chloride The chloride ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects th ...

chloride
, whereas within cells it is
potassium Potassium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, b ...

potassium
and other
phosphate In chemistry, a phosphate is an anion, salt (chemistry), salt, functional group or ester derived from a phosphoric acids and phosphates, phosphoric acid. It most commonly means orthophosphate, a derivative of phosphoric acid, orthophosphoric a ...

phosphate
s.


Cells

The body contains trillions of
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
, 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 An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
of the body and
cell types A cell type is a classification used to distinguish between morphologically or phenotypically distinct cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell ...
. The body is also host to about the same number of non-human cells as well as
multicellular organisms Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Out ...

multicellular organisms
which reside in the
gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, d ...
and on the skin. Not all parts of the body are made from cells. Cells sit in an
extracellular matrix In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
that consists of proteins such as
collagen Collagen () is the main structural protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowder ...

collagen
, 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 Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
. DNA sits within the
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

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 polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
. The RNA is then used to
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
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 ''erythros'' for "red" and ''kytos'' for "holl ...

red blood cells
lose their nucleus as they mature.


Tissues

The body consists of many different types of
tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubitata'', a species of geometer mot ...
, defined as cells that act with a specialised function. The study of tissues is called
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

histology
and often occurs with a
microscope A microscope (from grc, μικρός ''mikrós'' 'small' and ''skopeîn'' 'to look (at); examine, inspect') is a used to examine objects that are too small to be seen by the . is the of investigating small objects and structures using a ...

microscope
. The body consists of four main types of tissues. These are lining cells (
epithelia Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume ...
),
connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions ...
,
nerve tissue Nervous tissue, also called neural tissue, is the main tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in ...
and
muscle tissue Muscle tissues are soft tissue of a tendon A tendon or sinew is a tough band of fibrous connective tissue that connects muscle to bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton i ...

muscle tissue
. Cells that lie on surfaces exposed to the outside world or gastrointestinal tract (
epithelia Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume ...
) or internal cavities (
endothelium Endothelium is a single layer of squamous Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. Wit ...
) come in numerous shapes and forms – from single layers of flat cells, to cells with small beating hair-like
cilia The cilium (; the plural is cilia) is an organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, ...

cilia
in the lungs, to column-like cells that line the
stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilated structure and functions as a vital organ. In the digestive system the stomach is involved in the second phase of digestion, ...

stomach
. 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 An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
, structured collections of
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
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 differ ...

skin
. Examples include the
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
,
lung The lungs are the primary organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma ...

lung
s and
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's t ...

liver
. Many organs reside within
cavitiesA cavity is a hollow in an object. Biology and healthcare *Cavity or Tooth decay, dental caries, damage to the structure of a tooth *Body cavity, a fluid filled space in many animals where organs typically develop **The gastrovascular cavity, which ...
within the body. These cavities include the
abdomen The abdomen (colloquially called the belly, tummy, midriff 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 Trunk (anatomy) ...
(which contains the stomach, for example) and
pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology ...
, which contains the lungs.


Heart

The heart is an organ located in the
thoracic cavity 250px, The picture displays the Mediastinum on sagittal plane, Thoracic diaphragm">sagittal_plane.html" ;"title="Mediastinum on sagittal plane">Mediastinum on sagittal plane, Thoracic diaphragm at the bottom, the heart (Cor), behind Sternum and ...
between the
lungs The lungs are the primary organs of 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 animal ...

lungs
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 The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory syst ...

pericardium
which holds it in place in the
mediastinum The mediastinum (from ) is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax The thorax or chest is a part of the anatomy of hu ...

mediastinum
and serves to protect it from blunt trauma,
infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may ...

infection
and help lubricate the movement of the heart via
pericardial fluidImage:Gray968.png, 300px, A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum. The pleural and pericardial cavities are exaggerated since normally there is no space between parietal and visceral pleura ...
. The heart works by pumping blood around the body allowing
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
nutrients A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and ta ...
,
waste Waste (or wastes) are unwanted or unusable materials. Waste is any substance which is discarded after primary use, or is worthless, defective and of no use. A by-product A by-product or byproduct is a secondary product derived from a produ ...
,
hormones A hormone (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 m ...

hormones
and
white blood cells 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 ...
to be transported. 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 and adjacent deflections. Re the cardiac cycle, ''atrial systole'' begins at the P wave; ''ventricular systole'' begins at the Q deflection of the QRS complex. The cardiac cycle is the performance of the human heart from the beginning of one he ...
. This allows enough blood to get into the ventricles during
atrial systole and adjacent deflections. Re the cardiac cycle, ''atrial systole'' begins at the P wave; ''ventricular systole'' begins at the Q deflection of the QRS complex. The cardiac cycle is the performance of the human heart from the beginning of one he ...
. 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 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 a group of Cell (biology), cells known as pacemaker cells, located in the wall of the atrium (heart), right atrium of the heart. These cells can produce an electric ...
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 is a part of the electrical conduction system of the heart The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node to cause contraction of the heart muscle. Th ...
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), or simply heart disease, involves the reduction of blood flow to the heart muscle Cardiac muscle (also called heart muscle or myocardium) i ...
is the leading cause of death worldwide, making up 16% of all deaths.It is caused by the buildup of in the
coronary arteries The coronary arteries are the arterial blood vessels of coronary circulation Coronary circulation is the circulation of blood in the blood vessels that supply the cardiac muscle, heart muscle (myocardium). Coronary arteries supply oxygen saturat ...

coronary arteries
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 or myocardium) is one of three types of vertebrate muscles, with the other two being skeletal muscle, skeletal and smooth muscle, smooth muscles. It is involuntary, striated muscle tissue, striated muscle t ...

myocardium
, a condition known as , this can cause
heart failure Heart failure (HF), also known as congestive heart failure (CHF) and (congestive) cardiac failure (CCF), is a set of manifestations caused by the failure of the heart The heart is a cardiac muscle, muscular Organ (biology), organ in mo ...
or
cardiac arrest Cardiac arrest is a sudden loss of blood flow Hemodynamics American and British English spelling differences#ae and oe, or haemodynamics are the Fluid dynamics, dynamics of blood flow. The circulatory system is controlled by homeostasis, homeost ...
and eventually death. Risk factors for coronary artery disease include
obesity Obesity is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. ...
,
smoking Smoking is a practice in which a substance is burned and the resulting smoke Smoke is a collection of airborne and es emitted when a material undergoes or , together with the quantity of air that is or otherwise mixed into the ma ...
,
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), a ...
,
high blood pressure Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank ...

high blood pressure
,
lack of exercise Increases in sedentary behaviors such as watching television are characteristic of a sedentary lifestyle A sedentary lifestyle is a type of lifestyle involving little or no physical activity Physical activity is defined as any voluntary bod ...
and
diabetes Diabetes mellitus, commonly known as just diabetes, is a group of metabolic disorders characterized by a hyperglycemia, high blood sugar level over a prolonged period of time. Symptoms often include frequent urination, Polydipsia, increased th ...

diabetes
. 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 cancer Cancer is a group of diseases involving ...
from another part of the body such as the
lungs The lungs are the primary organs of 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 animal ...

lungs
or
breasts The breast is one of two prominences located on the upper ventral region of the torso of primates. In females, it serves as the mammary gland, which produces and secretes milk to feed infants. Both females and males develop breasts from the s ...

breasts
. This is because the quickly stop dividing and all growth occurs through rather than
cell division Cell division is the process by which a parent cell (biology), cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division; a vegetative ...

cell division
.


Gallbladder

The gallbladder is a hollow pear shaped organ located posterior to the inferior middle part of the
right lobe of the liver The human liver is divided Gross anatomy, grossly into four parts or Lobe (anatomy), lobes. The four lobes are the right lobe, the left lobe, the caudate lobe, and the quadrate lobe. Seen from the front – the Thoracic diaphragm, diaphragmatic sur ...

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 of most s that aids the of s in the . In humans, bile is produced continuously by the liver (liver bile) and stored and concentrated in the . After ...
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 The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive sy ...
to help with digestion of fats. It receives bile from the
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's t ...

liver
via the
cystic duct The cystic duct is the short duct that joins the gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow Organ (anatomy), organ where bile is stored and concentrated before it is released into the sma ...
which connects to the
common hepatic duct The common hepatic duct is the first part of the biliary tract The biliary tract, (biliary tree or biliary system) refers to the liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue ...
to form the
common bile duct The common bile duct, sometimes abbreviated as CBD, is a duct in the gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive sy ...
. The gallbladder gets its blood supply from the
cystic artery The cystic artery (also known as bachelor artery) supplies oxygenated blood to the gallbladder In vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that ...
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 The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Pl ...
.
Gallstones A gallstone is a calculus (medicine), stone formed within the gallbladder out of precipitated bile components. The term cholelithiasis may refer to the presence of gallstones or to any disease caused by gallstones, and choledocholithiasis refers ...

Gallstones
is a common disease in which one or more stones form in the gallbladder or
biliary tract The biliary tract, (biliary tree or biliary system) refers to the liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal ...
. 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 In vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biologi ...
. Having gallstones is a risk factor for
gallbladder cancer Gallbladder cancer is a relatively uncommon cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not sp ...
which although quite uncommon is rapidly fatal if not diagnosed early.


Systems


Circulatory system

The
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertai ...
consists of the
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
and
blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a comp ...
s (
arteries An artery (plural arteries) () is a blood vessel 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 pulmonary arteries, pulmonary ...

arteries
,
vein Veins are blood vessels The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A b ...

vein
s and
capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules. These microvessel ...

capillaries
). The heart propels the circulation of the blood, which serves as a "transportation system" to transfer
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
, fuel, nutrients, waste products, immune cells and signalling molecules (i.e.
hormones A hormone (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 m ...
) 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, which pumps blood to the lungs to receive
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
and leave
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, 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 Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
in the circulation, including some that move from tissue to blood vessels and back, as well as the
spleen The spleen is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's ...

spleen
and
bone marrow Bone marrow is a semi-solid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphos ...
.


Digestive system

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

digestive system
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 ...

tongue
and
teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. ...
,
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American E ...

esophagus
,
stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilated structure and functions as a vital organ. In the digestive system the stomach is involved in the second phase of digestion, ...

stomach
, (
gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, d ...
,
small Small may refer to: Science and technology * SMALL Small may refer to: Science and technology * SMALL Small may refer to: Science and technology * SMALL, an ALGOL-like programming language * Small (anatomy), the lumbar region of the back * Sm ...

small
and
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human dig ...

large intestine
s, and
rectum The rectum is the final straight portion of the 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 vertebrates. Water is absorbed here and the re ...

rectum
), as well as the
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's t ...

liver
,
pancreas The pancreas is an Organ (anatomy), organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity, abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine ...

pancreas
, gallbladder, and salivary glands. It converts food into small, nutritional, non-toxic molecules for distribution and absorption into the body. These molecules take the form of
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s (which are broken down into amino acids), fats, vitamins and minerals (the last of which are mainly ionic rather than molecular). After being Swallowing, swallowed, food moves through the
gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, d ...
by means of peristalsis: the systematic expansion and contraction of muscles to push food from one area to the next. Digestion begins in the mouth, which Chewing, chews food into smaller pieces for easier digestion. Then it is Swallowing, swallowed, and moves through the
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American E ...

esophagus
to the
stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilated structure and functions as a vital organ. In the digestive system the stomach is involved in the second phase of digestion, ...

stomach
. In the stomach, food is mixed with gastric acids to allow the extraction of nutrients. What is left is called chyme; this then moves into the small intestine, which absorbs the nutrients and water from the chyme. What remains passes on to the
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human dig ...

large intestine
, where it is dried to form feces; these are then stored in the
rectum The rectum is the final straight portion of the 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 vertebrates. Water is absorbed here and the re ...

rectum
until they are expelled through the anus.


Endocrine system

The endocrine system consists of the principal endocrine glands: the pituitary, thyroid, adrenals,
pancreas The pancreas is an Organ (anatomy), organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity, abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine ...

pancreas
, parathyroids, and gonads, but nearly all organs and tissues produce specific endocrine hormones 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 consists of the white blood cells, the thymus, lymph nodes and lymph channels, which are also part of the lymphatic system. 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, cytokines, and toll-like receptors, among many others.


Integumentary system

The integumentary system consists of the covering of the body (the skin), including hair and nail (anatomy), nails as well as other functionally important structures such as the sweat glands and sebaceous glands. The skin provides containment, structure, and protection for other organs, and serves as a major sensory interface with the outside world.


Lymphatic system

The lymphatic system 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 consists of the human skeleton (which includes bones, ligaments, tendons, and cartilage) and attached muscles. It gives the body basic structure and the ability for movement. In addition to their structural role, the larger bones in the body contain
bone marrow Bone marrow is a semi-solid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphos ...
, the site of production of blood cells. Also, all bones are major storage sites for Calcium in biology, calcium and
phosphate In chemistry, a phosphate is an anion, salt (chemistry), salt, functional group or ester derived from a phosphoric acids and phosphates, phosphoric acid. It most commonly means orthophosphate, a derivative of phosphoric acid, orthophosphoric a ...

phosphate
. This system can be split up into the muscular system and the skeletal system.


Nervous system

The nervous system consists of the body's neurons and glial cells, which together form the nerves, ganglia and gray matter which in turn form the brain and related structures. The brain is the organ of thought, emotion, memory, and sensory processing; it serves many aspects of communication and controls various systems and functions. The special senses consist of Visual perception, vision, Hearing (sense), hearing, taste, and olfaction, smell. The human eye, eyes, ears,
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 ...

tongue
, and nose gather information about the body's environment. From a structural perspective, the nervous system is typically subdivided into two component parts: the central nervous system (CNS), composed of the brain and the spinal cord; and the peripheral nervous system (PNS), composed of the nerves and ganglion, ganglia outside the brain and spinal cord. The CNS is mostly responsible for organizing motion, processing Sense, sensory information, thought, memory, cognition 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 central nervous system, CNS directly gives rise to consciousness. The peripheral nervous system (PNS) is mostly responsible for gathering information with sensory neurons and directing body movements with motor neurons. From a functional perspective, the nervous system is again typically divided into two component parts: the somatic nervous system (SNS) and the autonomic nervous system (ANS). The SNS is involved in voluntary functions like speech, speaking and sense, sensory processes. The ANS is involved in involuntary processes, such as digestion and regulating blood pressure. The nervous system is subject to many different diseases. In epilepsy, abnormal electrical activity in the brain can cause epileptic seizure, seizures. In multiple sclerosis, the immune system attacks the myelin, nerve linings, damaging the nerves' ability to transmit signals. Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a motor neuron 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, children and ensure their Puberty, sexual development so that they can produce new humans too. It is composed of the Gonad, gonads (Testicle, testes and Ovary, ovaries) which produce Egg cell, eggs and Spermatozoon, sperm cells (Gamete, gametes) and produce Sex hormone, hormones necessary for proper Puberty, sexual development. The rest of the Gland, glands and ducts of the reproductive system are responsible for the transportation and sustaining of the Gamete, gametes and to Pregnancy, nurture the offspring. The reproductive system is first stimulated by the hypothalamus during puberty which causes the Ovary, ovaries and Testicle, testes to produce testosterone (male) and estrogen and progesterone (female). Male puberty generally occurs between the ages of 13-15 and is characterized by beginning of Spermatogenesis, sperm production and the development of Secondary sex characteristic, secondary sex characteristics such as increased height and weight, broadened shoulders, Pubic hair, pubic and facial hair, voice deepening and muscle development. Female puberty generally occurs between the ages of 9-13 and is characterized by ovulation and menstruation. The growth of secondary sex characteristics such as growth of Pubic hair, pubic and underarm hair, breast, Uterus, uterine and Vagina, vaginal growth, widening hips and increased height and weight also occur during the female puberty process. The external male reproductive system is made up of the penis and the scrotum which is a bag that protects the testes. The penis consists of the Glans penis, glans which is the head of the penis and contains the urethra and urinary meatus the point where urine exits the penis, the rest of the penis is called the Corpus cavernosum penis, shaft or corpus cavernosum and contains most of the urethra. The glans is covered by a fold of skin called the foreskin though this can be removed through circumcision. Internally the male reproductive system starts in the testes where hundreds of Seminiferous tubule, seminiferous tubules produce sperm which is then stored and matured into spermatozoon in the epididymis. They are then brought through the vas deferens which leads away from the testes to the seminal vesicles where the sperm cells are mixed with a fructose-rich fluid from the seminal vesicles allowing the sperm to stay alive and remain healthy. It is then brought by the ejaculatory duct through the prostate and bulbourethral gland, and mixed with fluids from said glands. The Prostatic fluid, 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 and is released through the urethra during ejaculation. Almost the entire internal male reproductive system works in pairs with two Testicle, testes, two epididymis, two vas deferens, two seminal vesicles, two Ejaculatory duct, ejaculatory ducts, two Bulbourethral gland, bulbourethral glands, but only one prostate and urethra. The external female reproductive system also called the vulva consists of the mons pubis a fatty mass that covers the Pubis (bone), pubis, the labia majora (outer lips of the vagina), the labia minora (inner lips of the vagina), the Vagina, vaginal opening which opens into vagina and is where the penis is inserted during sexual intercourse and Childbirth, children are born, the urethral opening which is the opening for the urethra that carries urine from the Urinary bladder, bladder and the clitoris which contains the most sensitive nerve endings and in humans has no use other than Sexual stimulation, sexual pleasure. Located between the anus and vagina is the perineum. Internally the female reproductive system contains two Ovary, ovaries, the uterus, two Fallopian tube, fallopian tubes and the cervix. At birth a female has about 700,000 Oocyte, oocytes (the immature version of the egg cell) in both ovaries combined, though this degenerates to about 400,000 by the time puberty is reached. This is a lifetime supply as after birth no more Oocyte, oocytes are produced, compared to males where Spermatozoon, sperm cells are produced during their entire lifetime. During puberty the menstrual cycle begins for the first time, in response to low estrogen and progesterone levels the hypothalamus releases Gonadotropin-releasing hormone, gonadotropin releasing hormone (GnRH). This causes the Anterior pituitary, anterior pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates Ovarian follicle, ovarian follicles to grow and one dominant follicle will eventually take over. As it continues to grow it releases more and more estradiol which stimulates LH secretion and suppresses FSH secretion preventing further follicular growth. When Luteinizing hormone, LH levels are highest the follicle ruptures releasing the Egg cell, ovum in a process called ovulation where it is then moved to one of the Fallopian tube, fallopian tubes. 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 progesterone causes the endometrium to grow thick preparing it for implantation of a Zygote, fertilized egg. If fertilization occurs the corpus luteum continues to secrete hormones until the placenta develops enough to secrete the necessary hormones for maintaining pregnancy. Eventually the corpus luteum will turn into corpus albicans which is essentially scar tissue. If fertilization fails the corpus luteum will degrade into corpus albicans and stop secreting enough progesterone and estrogen causing the Endometrium, endometrial lining to break resulting in menstruation. Many diseases affect the reproductive system such as polycystic ovary syndrome (PCOS) which is characterized by Hyperandrogenism, elevated androgen levels, Irregular menstruation, menstrual irregularities and/or small Ovarian cyst, cysts 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, weight gain, Pattern hair loss, male pattern baldness and irregular menstruation. Another reproductive disease is testicular torsion, it occurs when the spermatic cord which holds up the testicle wraps around itself cutting off Ischemia, blood flow to the testicle. Testicular torsion is a medical emergency and can result in testicular death or infertility if not treated immediately by physically unwrapping the spermatic cord. If the testicle has suffered Infarction, severe damage, it may need to be surgically in a lateral orchiectomy. The primary symptom of testicular torsion is severe testicular pain 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 such as syphilis, HIV, chlamydia, Human papillomavirus infection, HPV and Genital wart, genital warts are spread through sexual intercourse including Oral sex, oral, vaginal and anal sex. Many of these infections can be lethal if left untreated though others are mostly Benignity, harmless. Cancer can affect many parts of the reproductive system including Penile cancer, the penis, Testicular cancer, testicles, Prostate cancer, prostate, Ovarian cancer, ovaries, Cervical cancer, cervix, Vaginal cancer, vagina, Fallopian tube cancer, fallopian, Uterine cancer, uterus and Vulvar cancer, vulva.


Respiratory system

The respiratory system consists of the nose, nasopharynx, Vertebrate trachea, trachea, and lungs. It brings oxygen from the air and excretes
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and water back into the air. First, Atmosphere of Earth, air is pulled through the trachea into the lungs by the thoracic diaphragm, diaphragm pushing down, which creates a vacuum. Air is briefly stored inside small sacs known as Pulmonary alveolus, alveoli (sing.: alveolus) before being expelled from the lungs when the diaphragm contracts again. Each alveolus is surrounded by Capillary, capillaries carrying deoxygenated blood, which absorbs oxygen out of the air and into the bloodstream."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 of the lungs and excess mucus are common sources of breathing difficulties. In asthma, the respiratory system is persistently inflamed, causing Wheeze, wheezing and/or shortness of breath. Pneumonia occurs through
infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may ...

infection
of the alveoli, and may be caused by tuberculosis. Chronic obstructive pulmonary disease, Emphysema, commonly a result of smoking, is caused by damage to connections between the alveoli.


Urinary system

The urinary system consists of the two kidneys, two ureters, Urinary bladder, bladder, and urethra. It removes waste materials from the blood through urine, which carries a variety of waste molecules and excess ions and water out of the body. First, the Kidney, kidneys filter the blood through their respective Nephron, nephrons, removing Metabolic waste, waste products like urea, creatinine and maintaining the Electrolyte imbalance, proper balance of Electrolyte, electrolytes and turning the waste products into urine 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 Ureter, ureters from the kidneys down to the Urinary bladder, bladder. The smooth muscle lining the ureter walls continuously tighten and relax through a process called peristalsis 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. It stores urine until the brain signals it to relax the Urethral sphincters, urinary sphincter and release the urine into the urethra starting urination. A normal bladder can hold up to 16 ounces (half a liter) for 3-5 hours comfortably. Numerous Urologic disease, diseases affect the urinary system including Kidney stone disease, kidney stones which are formed when materials in the urine concentrate enough to form a solid mass, Urinary tract infection, urinary tract infections which are infections of the urinary tract and can cause pain when urinating, frequent urination and even death if left untreated. Kidney failure, Renal failure 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 can affect the Bladder cancer, bladder, Kidney cancer, kidneys, Urethral cancer, urethra and Ureteral cancer, ureters with the latter two being far more rare.


Anatomy

Human
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It ...

anatomy
is the study of the shape and form of the human body. The human body has four limb (anatomy), limbs (two arms and two legs), a head and a
neck The neck is the part of the body on many vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

neck
which connect to the torso. The body's shape is determined by a strong human skeleton, skeleton made of bone and cartilage, surrounded by fat, muscle, connective tissue, organs, and other structures. The Vertebral column, spine at the back of the skeleton contains the flexible vertebral column which surrounds the spinal cord, which is a collection of nerve fibres connecting the brain to the rest of the body. Nerves 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 variations such as sesamoid bones and accessory muscles. Blood vessels carry blood throughout the body, which moves because of the beating of the
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
. Venules and
vein Veins are blood vessels The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A b ...

vein
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 vena cava, superior and inferior vena cava, which drain blood into the right side of the heart. From here, the blood is pumped into the
lung The lungs are the primary organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma ...

lung
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, the aorta, and then progressively smaller arteries and arterioles until it reaches tissue. Here blood passes from small arteries into capillaries, then small veins and the process begins again. Blood carries
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
, waste products, and hormones from one place in the body to another. Blood is filtered at the kidneys and
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's t ...

liver
. The body consists of a number of body cavity, body cavities, separated areas which house different organ systems. The brain and central nervous system reside in an area protected from the rest of the body by the blood brain barrier. The lungs sit in the pleural cavity. The intestines,
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's t ...

liver
, and
spleen The spleen is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's ...

spleen
sit in the abdominal cavity. Height, weight, Body shape, shape and other body proportions vary individually and with age and sex. Body shape is influenced by the distribution of bones, muscle and fat tissue.


Physiology

Human
physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
is the study of how the human body functions. This includes the mechanical, physical, Bioelectromagnetism, bioelectrical, and Biochemistry, biochemical functions of humans in good health, from
organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
to the
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
of which they are composed. The human body consists of many interacting systems of organs. These interact to maintain
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
, 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. The nervous system receives information from the body, and transmits this to the brain via nerve impulses and neurotransmitters. At the same time, the endocrine system releases hormones, such as to help regulate blood pressure 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 of a female is penetrated by sperm. The egg then lodges in the uterus, where an embryo and later fetus develop until childbirth, birth. 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, adolescence, and through adulthood to old age, and are referred to as the process of aging.


Society and culture


Professional study

Health professionals learn about the human body from illustrations, models, and demonstrations. Medical and dental students in addition gain practical experience, for example by dissection of cadavers. Human anatomy,
physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
, and biochemistry 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 wrote his ''Canon'' on the Mathematics and art#Polykleitos, ideal proportions of the male nude. In the Italian Renaissance, artists from Piero della Francesca (c. 1415–1492) onwards, including Leonardo da Vinci (1452–1519) and his collaborator Luca Pacioli (c. 1447–1517), learnt and wrote about the rules of art, including visual perspective and the proportions of the human body.


History of anatomy

In Ancient Greece, the ''Hippocratic Corpus'' 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, Andreas Vesalius (1514–1564) pioneered the modern study of human anatomy by dissection, writing the influential book ''De humani corporis fabrica''. Anatomy advanced further with the invention of the
microscope A microscope (from grc, μικρός ''mikrós'' 'small' and ''skopeîn'' 'to look (at); examine, inspect') is a used to examine objects that are too small to be seen by the . is the of investigating small objects and structures using a ...

microscope
and the study of the cellular structure of tissues and organs. Modern anatomy uses techniques such as magnetic resonance imaging, X-ray computed tomography, computed tomography, fluoroscopy and Medical ultrasonography, ultrasound imaging to study the body in unprecedented detail.


History of physiology

The study of human physiology began with Hippocrates in Ancient Greece, around 420 BCE, and with Aristotle (384–322 BCE) who applied critical thinking and emphasis on the relationship between structure and function. Galen (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 (1497–1558). In the 17th century, William Harvey (1578–1657) described the
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertai ...
, 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 of Matthias Jakob Schleiden, Matthias Schleiden and Theodor Schwann in 1838, that organisms are made up of cells. Claude Bernard (1813–1878) created the concept of the ''milieu interieur'' (internal environment), which Walter Cannon (1871–1945) later said was regulated to a steady state in
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
. In the 20th century, the physiologists Knut Schmidt-Nielsen and George Bartholomew (biologist), George Bartholomew extended their studies to comparative physiology and ecophysiology. Most recently, evolutionary physiology has become a distinct subdiscipline.


See also

* * * * * * * * * Outline of human anatomy * Organ system


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 Human body, Human physiology, Human anatomy,