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, entertainment, and media * ''Network'' (1976 film), a 1976 American film * ''Network'' (2019 film), an Indian film * ...

that permits

blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood

to circulate and transport

nutrient 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 t ...

s (such as

amino acids Amino acids are organic compounds that contain amino (–NH2) and Carboxylic acid, carboxyl (–COOH) functional groups, along with a Substituent, side chain (R group) specific to each amino acid. The key Chemical element, elements of an amino ...

and

electrolytes An electrolyte is a medium containing ions that is electrically conducting Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resist ...

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 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 ...

hormone 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 ...

hormone

s, and

blood cell A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell 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 ...

s to and from 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 ...

in the body to provide nourishment and help in fighting diseases, stabilize temperature and

, and maintain

homeostasis In , homeostasis is the state of steady internal, , and conditions maintained by . This is the condition of optimal functioning for the organism and includes many variables, such as and , being kept within certain pre-set limits (homeostatic r ...

. The circulatory system includes the

lymphatic system The lymphatic system, or lymphoid system, is an in vertebrates that is part of the and the . It is made up of a large network of lymph, s, lymph nodes, lymphatic or lymphoid organs, and lymphoid tissues. The vessels carry a clear fluid called ...

, which circulates

lymph Lymph (from Latin, ''lympha'' meaning "water") is the fluid that flows through the lymphatic system The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the circulatory system and the immune system. It is ...

. The passage of lymph takes much longer than that of blood. Blood is a fluid consisting of

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood plasma ...

red blood cell 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 Greek may refer to: Greece Anything of, from ...

white blood cell White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ...

s, and

platelets Platelets, also called thrombocytes (from Greek#REDIRECT 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. ...

that is circulated by 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 system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste ...

heart

through the vertebrate vascular system, carrying oxygen and nutrients to and waste materials away from all body tissues. Lymph is essentially recycled excess blood plasma after it has been filtered from the

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, ...

(between cells) and returned to the lymphatic system. The cardiovascular (from Latin words meaning "heart" and "vessel") system comprises the blood, 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 that permits blood to circulate and transport nutrients (such as amino ...

s. The lymph,

lymph node A lymph node, or lymph gland, is a kidney-shaped Organ (anatomy), 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 lymphocy ...

s, and lymph vessels form the lymphatic system, which returns filtered blood plasma from the interstitial fluid (between cells) as lymph. The circulatory system of the blood has two components, a systemic circulation and a pulmonary circulation. While humans and other

vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...

have a closed cardiovascular system (which means that the blood never leaves the network of

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 ...

veins 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 vein, pulmonary and umbilical veins, both of which ca ...

veins

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 ...

), some

invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart from the chordata, chordate subphylum vertebrate, Vertebra ...

groups have an open cardiovascular system. The lymphatic system, in contrast, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood. The more primitive,

diploblastic Diploblasty is a condition of the blastula Blastulation is the stage in early animal embryonic development that produces the blastula. The blastula (from Greek '' βλαστός'' ( meaning ''sprout'') is a hollow sphere of cells ( blastomere ...

animal phyla lack circulatory systems. Many diseases affect the circulatory system. This includes

cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), or simpl ...

, affecting the cardiovascular system, and lymphatic disease affecting the lymphatic system.

Cardiologist Cardiology (from 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 mil ...

s are medical professionals which specialise in the heart, and

cardiothoracic surgeon Cardiothoracic surgery is the medical speciality, field of medicine involved in surgery, surgical treatment of organs inside the thoracic cavity — generally treatment of conditions of the heart (heart disease), lungs (pulmonology, lung disease) ...

s specialise in operating on the heart and its surrounding areas.

Vascular surgeon Vascular surgery is a surgical subspecialty in which diseases of the vascular system, or arteries, veins and lymphatic circulation, are managed by medical therapy, minimally-invasive catheter procedures, and surgical reconstruction. The specialty ...

s focus on other parts of the circulatory system.

Structure

Cardiovascular system

The essential components of the human cardiovascular system are the

and

s. It includes the

pulmonary circulation The mammalian heart is divided between the systemic and the pulmonary circulation, generally agreed upon as left and right sided circuits. The right circuit is the portion of the circulatory system The circulatory system, also called the ca ...

, a "loop" through 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 blood is oxygenated; and the systemic circulation, a "loop" through the rest of the body to provide

oxygenate Oxygenated chemical compounds contain oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical re ...

d blood. The systemic circulation can also be seen to function in two parts – a ''macrocirculation'' and a

microcirculation The microcirculation is the circulation Circulation may refer to: Science and technology * Atmospheric circulation, the large-scale movement of air * Circulation (physics), the path integral of the fluid velocity around a closed curve in a flui ...

. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of their total body weight. Blood consists of

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 ...

white blood cells White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ...

, and

. Also, the

digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus which includes all the organs of th ...

works with the circulatory system to provide the nutrients the system needs to keep the

pumping. The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of

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 biological system is a comp ...

. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enter

, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction. The other component of the circulatory system, the

, is open.

Arteries

Oxygenated blood enters the systemic circulation when leaving the

left ventricle A ventricle is one of two large chambers toward the bottom of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries ...

, through the

aortic semilunar valve

. The first part of the systemic circulation is the

aorta The aorta ( ) is the main and largest in the , originating from the of the and extending down to the , where it into two smaller arteries (the ). The aorta distributes blood to all parts of the body through the . Structure Sections In a ...

aorta

, a massive and thick-walled artery. The aorta arches and gives branches supplying the upper part of the body after passing through the aortic opening of the diaphragm at the level of thoracic ten vertebra, it enters the abdomen. Later it descends down and supplies branches to abdomen, pelvis, perineum and the lower limbs. The walls of aorta are elastic. This elasticity helps to maintain the

blood pressure Blood pressure (BP) is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motio ...

throughout the body. When the aorta receives almost five litres of blood from the heart, it recoils and is responsible for pulsating blood pressure. Moreover, as aorta branches into smaller arteries, their elasticity goes on decreasing and their compliance goes on increasing.

Capillaries

Arteries branch into small passages called

arteriole An arteriole is a small-diameter 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 that permits blood to c ...

s and then into the

. The capillaries merge to bring blood into the venous system.

Veins

Capillaries merge into

venule A venule is a very small 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 a ...

s, which merge into

. The venous system feeds into the two major veins: the

superior vena cava The superior vena cava (SVC) is the anatomical terms of location#Superior and inferior, superior of the two venae cavae, the great vein, venous trunks that return deoxygenated blood from the circulatory system, systemic circulation to the atrium ...

– which mainly drains tissues above the heart – and the

inferior vena cava The inferior vena cava is a large vein that carries the deoxygenated blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance th ...

– which mainly drains tissues below the heart. These two large veins empty into the

right atrium The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the Ventricle (heart), ventricles of the heart. There are two atria in the human heart – the left atrium receives blood from the pulmonary (lung) circul ...

of the

Portal veins

The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart.

Portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approximat ...

s are a slight exception to this. In humans the only significant example is the

hepatic portal vein The portal vein or hepatic portal vein (HPV) is a 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 tis ...

which combines from capillaries around 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 ...

where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in 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

Heart

The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human

there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total:

left atrium The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the Ventricle (heart), ventricles of the heart. There are two atria in the human heart – the left atrium receives blood from the pulmonary (lung) circula ...

and

right ventricle A ventricle is one of two large chambers toward the bottom of 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 system. The pumped blood ...

. The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

Coronary vessels

The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation and derives very little from the blood contained within the four chambers. The coronary circulation system provides a blood supply to the

heart muscle Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biolo ...

itself. The coronary circulation begins near the origin of the

by two

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 ...

: the

right coronary artery In the coronary circulation, blood supply of the heart, the right coronary artery (RCA) is an artery originating above the right cusp of the aortic valve, at the Aortic sinus, right aortic sinus in the heart. It travels down the right coronary sul ...

and the

left coronary artery The left coronary artery (abbreviated LCA) is a coronary artery that arises from the aorta above the left cusp of the aortic valve, and feeds blood to the left side of the heart muscle. It is also known as the left main coronary artery (abbrevia ...

. After nourishing the heart muscle, blood returns through the coronary veins into the

coronary sinus The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the heart muscle (myocardium). It delivers less-oxygenated blood to the right atrium, as do the superior vena cava, superior and inferior v ...

and from this one into the right atrium. Back flow of blood through its opening 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 ...

is prevented by Thebesian valve. The

smallest cardiac veins The smallest cardiac veins, also known as the Thebesian veins, are small valveless 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 h ...

drain directly into the heart chambers.

Lungs

The circulatory system of the lungs is the portion of the cardiovascular system in which

-depleted

is pumped away from the heart, via the

pulmonary artery A pulmonary artery is an artery 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 t ...

, to 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 returned, oxygenated, to the heart via the

pulmonary vein The pulmonary veins are the 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 vein, pulmonary a ...

. Oxygen-deprived blood from the superior and inferior

vena cava The venae cavae (; from the Latin for "hollow veins", singular "vena cava" ) are two large veins (venous trunks) that return deoxygenated blood from the body into the heart. In humans there are the superior vena cava and the inferior vena cav ...

enters the right atrium of the heart and flows through the

tricuspid valve The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle A ventricle is one of two large chambers toward the bottom of the heart The heart i ...

(right atrioventricular valve) into the right ventricle, from which it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs.

Gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid ...

occurs in the lungs, whereby is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now oxygen-rich blood to the

. A separate system known as the

bronchial circulationThe bronchial circulation is the part of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an Biological system, organ system that permits blood to circulate and transport nutrients ( ...

supplies blood to the tissue of the larger airways of the lung.

Systemic circulation

Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart through the aorta from the left ventricle where the blood has been previously deposited from pulmonary circulation, to the rest of the body, and returns oxygen-depleted blood back to the heart.

Brain

The brain has a dual blood supply that comes from arteries at its front and back. These are called the "anterior" and "posterior" circulation respectively. The anterior circulation arises from the

internal carotid arteries The internal carotid artery (Latin: arteria carotis interna) is located in the inner side of the neck in contrast to the external carotid artery The external carotid artery is a major artery of the head and neck. It arises from the common caroti ...

and supplies the front of the brain. The posterior circulation arises from the

vertebral arteries The vertebral arteries are major artery, arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, mid ...

, and supplies the back of the brain and

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain A brain 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 anima ...

. The circulation from the front and the back join ( anastomise) at the

Circle of Willis The circle of Willis (also called Willis' circle, loop of Willis, cerebral arterial circle, and Willis polygon) is a circulatory anastomosis A circulatory anastomosis is a connection (an anastomosis) between two blood vessels, such as between art ...

Kidneys

The

renal circulation The kidneys are two reddish-brown bean-shaped organs found in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological ...

receives around 20% of the cardiac output. It branches from the

abdominal aorta The abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta (of the thorax). Structure The abdominal aorta begins at the level of the diaphragm (anatomy), diaphragm, ...

and returns blood to the ascending

. It is the blood supply to the

kidney The kidneys are two reddish-brown bean-shaped 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 ...

kidney

s, and contains many specialized blood vessels.

Lymphatic system

The

is part of the circulatory system in many complex animals such as mammals and birds. It is a network of

lymphatic vessel The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes) structured like blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels t ...

s and

lymph capillaries Lymph (from Latin, ''lympha'' meaning "water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituen ...

lymph nodes A lymph node, or lymph gland, is a kidney-shaped Organ (anatomy), 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 lymphocy ...

and

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 ...

, and lymphatic tissues and circulating

. One of its major functions is to carry the lymph, draining and returning

back towards the heart for return to the cardiovascular system, by emptying into the

lymphatic duct A lymph duct is a great lymphatic vessel that empties lymph Lymph (from Latin, ''lympha'' meaning "water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, near ...

s. Its other main function is in the

adaptive immune system The adaptive immune system, also referred as the acquired immune system, is a subsystem of the immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, ...

Development

The development of the circulatory system starts with

vasculogenesis Vasculogenesis is the process of blood vessel formation in the embryo, occurring by a ''De novo synthesis, de novo'' production of endothelial cells. It is sometimes paired with angiogenesis, as the first stage of the formation of the vascular netw ...

in the

embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo

. The human arterial and venous systems develop from different areas in the embryo. The arterial system develops mainly from the

aortic arches The aortic arches or pharyngeal arch arteries (previously referred to as branchial arches in human embryos) are a series of six paired embryological vascular structures which give rise to the great arteries An artery (plural arteries) () is ...

, six pairs of arches that develop on the upper part of the embryo. The venous system arises from three bilateral veins during weeks 4 – 8 of

embryogenesis An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

Fetal circulation In animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic r ...

begins within the 8th week of development. Fetal circulation does not include the lungs, which are bypassed via the

truncus arteriosus

. Before birth the

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism tha ...

fetus

obtains

(and

s) from the mother through the

placenta The placenta is a temporary fetal 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. ...

and the

umbilical cord In placental Placentalia is one of the three extant subdivisions of the class of animals Mammalia Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European l ...

Heart

Arteries

The human arterial system originates from the aortic arches and from the

dorsal aortae The dorsal aortae are paired (left and right) embryological vessels which progress to form the descending aorta The descending aorta is part of the aorta, the largest artery in the Human body, body. The descending aorta begins at the aortic arch ...

starting from week 4 of embryonic life. The first and second aortic arches regress and form only the maxillary arteries and stapedial arteries respectively. The arterial system itself arises from aortic arches 3, 4 and 6 (aortic arch 5 completely regresses). The dorsal aortae, present on the

dorsal Dorsal (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Repu ...

side of the embryo, are initially present on both sides of the embryo. They later fuse to form the basis for the

itself. Approximately thirty smaller arteries branch from this at the back and sides. These branches form the

intercostal arteries The intercostal arteries are a group of arteries that supply the area between the ribs ("costae"), called the intercostal space. The highest intercostal artery (supreme intercostal artery or superior intercostal artery) is an artery in the hum ...

, arteries of the arms and legs, lumbar arteries and the lateral sacral arteries. Branches to the sides of the aorta will form the definitive

renal The kidneys are two reddish-brown bean-shaped 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 ...

, suprarenal and gonadal arteries. Finally, branches at the front of the aorta consist of the

vitelline arteries The vitelline arteries are the arterial counterpart to the vitelline veins. Like the veins, they play an important role in the vitelline circulation of blood to and from the yolk sac of a fetus. They are a branch of the dorsal aorta. They give ris ...

and

umbilical arteries The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax The thorax or chest i ...

. The vitelline arteries form the

celiac

superior Superior may refer to: *Superior (hierarchy) In a hierarchy A hierarchy (from the Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) in which the items are represented as being "ab ...

and inferior mesenteric arteries of the gastrointestinal tract. After birth, the umbilical arteries will form the

internal iliac arteries The internal iliac artery (formerly known as the hypogastric artery) is the main artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the hum ...

Veins

The human venous system develops mainly from the vitelline veins, the

umbilical vein The umbilical vein is a 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 sys ...

s and the cardinal veins, all of which empty into the

sinus venosus The sinus venosus is a large quadrangular cavity which precedes the atrium on the venous side of the chordate A chordate () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biol ...

Function

Cardiovascular system

About 98.5% of the

in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with

hemoglobin Hemoglobin or haemoglobin (spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two distinct wa ...

molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in

mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...

s and many other species.

Lymphatic system

Clinical significance

Many diseases affect the circulatory system. These include a number of

s, affecting the cardiovascular system, and lymphatic diseases affecting the lymphatic system.

s are medical professionals which specialise in the heart, and

s specialise in operating on the heart and its surrounding areas.

s focus on other parts of the circulatory system.

Cardiovascular disease

Diseases affecting the cardiovascular system are called

. Many of these diseases are called "

lifestyle disease Lifestyle diseases can be defined as diseases linked with ones lifestyle. Lifestyle diseases are non-communicable disease A non-communicable disease (NCD) is a disease that is not transmission (medicine), transmissible directly from one person to ...

s" because they develop over time and are related to a person's exercise habits, diet, whether they smoke, and other lifestyle choices a person makes.

Atherosclerosis Atherosclerosis is a disease in which the wall of the artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels tr ...

is the precursor to many of these diseases. It is where small

atheromatous plaques An atheroma, or atheromatous plaque ("plaque"), is an abnormal accumulation of material in the tunica intima, inner layer of the wall of an artery. The material consists of mostly macrophage, macrophage cells, or debris, containing lipids, calciu ...

build up in the walls of medium and large arteries. This may eventually grow or rupture to occlude the arteries. It is also a risk factor for

acute coronary syndrome Acute coronary syndrome (ACS) is a syndrome (a set of signs and symptoms) due to decreased blood flow in the coronary arteries such that part of the heart muscle is unable to function properly or dies. The most common symptom is centrally l ...

s, which are diseases that are characterised by a sudden deficit of oxygenated blood to the heart tissue. Atherosclerosis is also associated with problems such as

aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the ca ...

formation or splitting ("dissection") of arteries. Another major cardiovascular disease involves the creation of a clot, called a "thrombus". These can originate in veins or arteries.

Deep venous thrombosis Deep vein thrombosis (DVT) is the formation of a blood clot A thrombus, colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and r ...

, which mostly occurs in the legs, is one cause of clots in the veins of the legs, particularly when a person has been stationary for a long time. These clots may embolise, meaning travel to another location in the body. The results of this may include

pulmonary embolus Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain pa ...

transient ischaemic attack A transient ischemic attack (TIA), commonly known as a mini-stroke, is a brief episode of neurological dysfunction caused by loss of blood flow (ischemia Ischemia or ischaemia is a restriction in blood Blood is a body fluid in humans and ...

s, or

stroke A stroke 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. Di ...

stroke

. Cardiovascular diseases may also be congenital in nature, such as

heart defects A congenital heart defect (CHD), also known as a congenital heart anomaly and congenital heart disease, is a defect in the structure of the heart or great vessels that is present at childbirth, birth. Signs and symptoms depend on the specific type ...

or persistent fetal circulation, where the circulatory changes that are supposed to happen after birth do not. Not all congenital changes to the circulatory system are associated with diseases, a large number are

anatomical variationAn anatomical variation, anatomical variant, or anatomical variability is a difference between the Anatomy, anatomical structures of animals from the same species. The variations are seen as normal in the sense that they are found consistently among ...

Investigations

The function and health of the circulatory system and its parts are measured in a variety of manual and automated ways. These include simple methods such as those that are part of the cardiovascular examination, including the taking of a person's

pulse In medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descriptive knowledge) ...

pulse

as an indicator of a person's

heart rate Heart rate is the speed of the heartbeat Heartbeat or heartbeats may refer to: Physiology *Cardiac cycle, of the heart *Contraction of the cardiac muscle, muscles of the heart, or a perceived effect of it, such as: **Heart sounds, the noises gene ...

, the taking of

through a

sphygmomanometer A sphygmomanometer ( ), also known as a blood pressure monitor, or blood pressure gauge, is a device used to measure blood pressure, composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner, and ...

or the use of a

stethoscope The stethoscope is an acoustic medical Medicine is the science and Praxis (process) , practice of caring for a patient, managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care , palliation o ...

to listen to the heart for murmurs which may indicate problems with the heart's valves. An

electrocardiogram Electrocardiography is the process of producing an electrocardiogram (ECG or EKG). It is a graph of voltage Voltage, electric potential difference, electromotive force emf, electric pressure or electric tension is the difference in elec ...

can also be used to evaluate the way in which electricity is conducted through the heart. Other more invasive means can also be used. A

cannula A cannula (; from Latin ''"little reed"''; plural ''cannulae'' or ''cannulas'') is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the ...

cannula

catheter In medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descriptive knowledge) ...

inserted into an artery may be used to measure

pulse pressure Pulse pressure is the difference between systolic and diastolic blood pressure Blood pressure (BP) is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (from grc, φυσική (ἐπιστήμ ...

pulmonary wedge pressure 110 px, Diagram of pulmonary artery catheter The pulmonary wedge pressure or PWP, or cross-sectional pressure (also called the pulmonary arterial wedge pressure or PAWP, pulmonary capillary wedge pressure or PCWP, or pulmonary artery occlusion press ...

s. Angiography, which involves injecting a dye into an artery to visualise an arterial tree, can be used in the heart (

coronary angiography A coronary catheterization is a minimally invasive procedure to access the coronary circulation and blood filled chambers of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the ...

) or brain. At the same time as the arteries are visualised, blockages or narrowings may be fixed through the insertion of

stent In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment or Palliative care , palliation of their ...

stent

s, and active bleeds may be managed by the insertion of coils. An MRI may be used to image arteries, called an

MRI angiogram

. For evaluation of the blood supply to the lungs a

CT pulmonary angiogram CT pulmonary angiogram (CTPA) is a medical diagnostic test that employs computed tomography (CT) angiography to obtain an image of the pulmonary arteries A pulmonary artery is an artery An artery (plural arteries) () is a blood vessel that tak ...

may be used. Vascular ultrasonography include for example: *

Intravascular ultrasound Intravascular ultrasound (IVUS) is a medical imaging methodology using a specially designed catheter with a miniaturized ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing ...

* Ultrasonography of deep venous thrombosis * Ultrasonography of chronic venous insufficiency of the legs

Surgery

There are a number of surgical procedures performed on the circulatory system: *

Coronary artery bypass surgery Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage") surgery, and colloquially heart bypass or bypass surgery, is a surgical procedure to reperfusion therapy, restore normal blood flow to an obs ...

Coronary stent A coronary stent is a tube-shaped device placed 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 ...

used in

angioplasty Angioplasty, also known as balloon angioplasty and percutaneous transluminal angioplasty (PTA), is a minimally invasive endovascular procedure used to widen narrowed or obstructed arteries or veins, typically to treat arterial atherosclerosis ...

Vascular surgery Vascular surgery is a surgical subspecialty in which diseases of the vascular system, or arteries, veins and lymphatic circulation, are managed by medical therapy, minimally-invasive catheter procedures, and surgical reconstruction. The specialty ...

Vein stripping Vein stripping is a surgical procedure done under general A general officer is an officer of high rank in the armies, and in some nations' air forces, space forces, or marines Marines or naval infantry, are typically a military force ...

* Cosmetic procedures Cardiovascular procedures are more likely to be performed in an inpatient setting than in an ambulatory care setting; in the United States, only 28% of cardiovascular surgeries were performed in the ambulatory care setting.

Society and culture

In Ancient Greece, the heart was thought to be the source of innate heat for the body. The circulatory system as we know it was discovered by

William Harvey William Harvey (1 April 1578 – 3 June 1657) was an English physician who made influential contributions in anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organis ...

Other animals

While humans, as well as other

, have a closed blood circulatory system (meaning that the blood never leaves the network of

and

), some

groups have an open circulatory system containing a heart but limited blood vessels. The most primitive,

animal phyla lack circulatory systems. An additional transport system, the lymphatic system, which is only found in animals with a closed blood circulation, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood. The blood vascular system first appeared probably in an ancestor of the triploblasts over 600 million years ago, overcoming the time-distance constraints of diffusion, while

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 ...

evolved in an ancestral

vertebrate Vertebrates () comprise all species 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 as an indiv ...

some 540–510 million years ago.

Open circulatory system

arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...

s, the open circulatory system is a system in which a fluid in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients, with there being no distinction between

and

; this combined fluid is called

hemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which ...

or haemolymph. Muscular movements by the animal during

locomotion Locomotion means the act or ability of an entity or person to transport or move oneself from place to place. Locomotion or Loco-Motion may refer to: Motion * Motion (physics) *Specific types of motion ** Animal locomotion *** Terrestrial locomoti ...

can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the

relaxes, blood is drawn back toward the heart through open-ended pores (ostia). Hemolymph fills all of the interior hemocoel of the body and surrounds all

. Hemolymph is composed of

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 ...

water

inorganic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they under ...

salts 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, behavior and the changes they undergo during ...

(mostly

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

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 ...

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 ...

magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

, and

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

organic compounds 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, behavior and the changes they undergo during ...

(mostly

carbohydrate A carbohydrate () is a 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 ...

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, and

lipid 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 ...

s). The primary oxygen transporter molecule is

hemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2). ...

. There are free-floating cells, the

hemocyte A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis Haematopoiesis (, from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ...

s, within the hemolymph. They play a role in the arthropod

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 Tumor immunology, cancer cells and objects such ...

Pseudoceros bifurcus - Blue Pseudoceros Flatworm

Closed circulatory system

The circulatory systems of all

s, as well as of

annelid The annelids (Annelida , from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...

s (for example,

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan A body plan, ''Bauplan'' (German plural ''Baupläne''), or ground plan is a set of morphological features common to man ...

s) and

cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the gram ...

s (

squid Squid are cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is ...

squid

octopus An octopus (pl. octopuses/octopi, see below for variants) is a soft-bodied, eight- limbed mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). A ...

octopus

es and relatives) always keep their circulating blood enclosed within heart chambers or blood vessels and are classified as ''closed'', just as in humans. Still, the systems of

fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish

amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...

reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile

s, and

bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird

s show various stages of the

evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

of the circulatory system. Closed systems permit blood to be directed to the organs that require it. In fish, the system has only one circuit, with the blood being pumped through the capillaries of the

gill A gill () is a respiratory organ that many aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent ...

s and on to the capillaries of the body tissues. This is known as ''single cycle'' circulation. The heart of fish is, therefore, only a single pump (consisting of two chambers). In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart. In reptiles, the

ventricular septum The interventricular septum (IVS, or ventricular septum, or during development septum inferius) is the stout wall separating the ventricles, the lower chambers of the heart The heart is a muscle, muscular Organ (anatomy), organ in most ani ...

of the heart is incomplete and the

is equipped with a

sphincter muscle A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the huma ...

. This allows a second possible route of blood flow. Instead of blood flowing through the pulmonary artery to the lungs, the sphincter may be contracted to divert this blood flow through the incomplete ventricular septum into the

and out through the

. This means the blood flows from the capillaries to the heart and back to the capillaries instead of to the lungs. This process is useful to

ectothermic ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an organism in which internal physiological sources of heat are of relatively ...

(cold-blooded) animals in the regulation of their body temperature. Birds, mammals, and

crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...

ns show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds and crocodilians evolved independently from that of mammals. Double circulatory systems permit blood to be repressurized after returning from the lungs, speeding up delivery of oxygen to tissues.

No circulatory system

Circulatory systems are absent in some animals, including

flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a count ...

s. Their

body cavity A body cavity is any space or compartment, or potential space Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social sciences to indicate things that are in a state w ...

has no lining or enclosed fluid. Instead, a muscular

pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx

leads to an extensively branched

that facilitates direct

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...

of nutrients to all cells. The flatworm's dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism.

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

can diffuse from the surrounding

into the cells, and

can diffuse out. Consequently, every cell is able to obtain nutrients, water and oxygen without the need of a transport system. Some animals, such as

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum In zoological nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Con ...

, have more extensive branching from their

gastrovascular cavity The gastrovascular cavity is the primary organ of digestion Digestion is the breakdown of large insoluble food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fung ...

(which functions as both a place of digestion and a form of circulation), this branching allows for bodily fluids to reach the outer layers, since the digestion begins in the inner layers.

History

Charta ex qva figvram parare convenit, illi qvae nervorvm seriem exprimit appendendam, 1543

The earliest known writings on the circulatory system are found in the

Ebers Papyrus The Ebers Papyrus, also known as Papyrus Ebers, is an Egyptian medical papyri, Egyptian medical papyrus of herbal knowledge dating to circa 1550 BC. Among the oldest and most important medical papyri of ancient Egypt, it was purchased at Luxor i ...

(16th century BCE), an ancient Egyptian medical papyrus containing over 700 prescriptions and remedies, both physical and spiritual. In the

papyrus Papyrus ( ) is a material similar to thick paper that was used in ancient times as a writing surface. It was made from the pith of the papyrus plant, ''Cyperus papyrus'', a wetland sedge. ''Papyrus'' (plural: ''papyri'') can also refer to a do ...

papyrus

, it acknowledges the connection of the heart to the arteries. The Egyptians thought air came in through the mouth and into the lungs and heart. From the heart, the air travelled to every member through the arteries. Although this concept of the circulatory system is only partially correct, it represents one of the earliest accounts of scientific thought. In the 6th century BCE, the knowledge of circulation of vital fluids through the body was known to the

Ayurvedic Ayurveda () is an alternative medicine Alternative medicine is any practice that aims to achieve the healing effects of medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and mana ...

physician

Sushruta Sushruta, or ''Suśruta'' (Sanskrit Sanskrit (, attributively , ''saṃskṛta-'', nominalization, nominally , ''saṃskṛtam'') is a classical language of South Asia belonging to the Indo-Aryan languages, Indo-Aryan branch of the Indo-Eu ...

ancient India According to consensus in modern genetics, anatomically modern humans first arrived on the Indian subcontinent from Africa between 73,000 and 55,000 years ago. Quote: "Y-Chromosome and Mt-DNA data support the colonization of South Asia by mod ...

. He also seems to have possessed knowledge of the

, described as 'channels' by Dwivedi & Dwivedi (2007).Dwivedi, Girish & Dwivedi, Shridhar (2007)
"History of Medicine: Sushruta – the Clinician – Teacher par Excellence"
, ''Indian J Chest Dis Allied Sci'' Vol. 49 pp. 243–244, National Informatics Centre (Government of India). The valves of the heart were discovered by a physician of the

Hippocratean

school around the 4th century BCE. However, their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for the transport of air. The Greek physician,

Herophilus Herophilos (; grc-gre, Ἡρόφιλος; 335–280 BC), sometimes Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around ...

, distinguished veins from arteries but thought that the

was a property of arteries themselves. Greek anatomist

Erasistratus Erasistratus (; grc-gre, Ἐρασίστρατος; c. 304 – c. 250 BC) was a Greek anatomist and royal physician under Seleucus I Nicator Seleucus I Nicator (; ; grc-gre, Σέλευκος Νικάτωρ, Séleukos Nikátōr, Seleucus the Vi ...

observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood. In 2nd-century AD

Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption = The te ...

Rome

, the

Greek#REDIRECT 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 million as of ...

physician

Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized Linguistic anglicisation (or anglicization, occasionally anglification, anglifying, or Englishing) is the practice of modi ...

knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves. Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through 'pores' in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created 'sooty' vapors were created and passed to the lungs also via the pulmonary artery to be exhaled. In 1025, ''

The Canon of Medicine ''The Canon of Medicine'' ( ar, القانون في الطب, italic=yes ''al-Qānūn fī al-Ṭibb''; fa, قانون در طب, italic=yes, ''Qanun-e dâr Tâb'') is an encyclopedia of medicine in five books compiled by Persian physician-phi ...

'' by the Persian physician,

Avicenna Ibn Sina ( fa, ابن سینا), also known as Abu Ali Sina (), Pur Sina (), and often known in the West as Avicenna (; – June 1037), was a Persian polymath who is regarded as one of the most significant physicians, astronomers, t ...

, "erroneously accepted the Greek notion regarding the existence of a hole in the ventricular septum by which the blood traveled between the ventricles." Despite this, Avicenna "correctly wrote on the

cardiac cycle The cardiac cycle is the performance of the human heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxy ...

s and valvular function", and "had a vision of blood circulation" in his ''Treatise on Pulse''. While also refining Galen's erroneous theory of the pulse, Avicenna provided the first correct explanation of pulsation: "Every beat of the pulse comprises two movements and two pauses. Thus, expansion : pause : contraction : pause. ..The pulse is a movement in the heart and arteries ... which takes the form of alternate expansion and contraction." In 1242, the Arabian physician,

Ibn al-Nafis Ala-al-Din abu al-Hasan Ali ibn Abi-Hazm al-Qarshi al-Dimashqi (Arabic Arabic (, ' or , ' or ) is a Semitic language that first emerged in the 1st to 4th centuries CE.Semitic languages: an international handbook / edited by Stefan Weninger ...

described the process of

in greater, more accurate detail than his predecessors, though he believed, as they did, in the notion of vital spirit (

pneuma ''Pneuma'' () is an ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following peri ...

), which he believed was formed in the left ventricle. Ibn al-Nafis stated in his ''Commentary on Anatomy in Avicenna's Canon'':

"...the blood from the right chamber of the heart must arrive at the left chamber but there is no direct pathway between them. The thick septum of the heart is not perforated and does not have visible pores as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (
pulmonary artery A pulmonary artery is an artery 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 t ...

) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (
pulmonary vein The pulmonary veins are the 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 vein, pulmonary a ...
) to reach the left chamber of the heart and there form the vital spirit..."

In addition, Ibn al-Nafis had an insight into what would become a larger theory of the

capillary A capillary is a small 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 that permits blood to circulate ...

circulation. He stated that "there must be small communications or pores (''manafidh'' in Arabic) between the pulmonary artery and vein," a prediction that preceded the discovery of the capillary system by more than 400 years. Ibn al-Nafis' theory, however, was confined to blood transit in the lungs and did not extend to the entire body.

Michael Servetus Michael Servetus (; es, Miguel Serveto as real name; french: Michel Servet; also known as ''Miguel Servet'', ''Miguel de Villanueva'', ''Revés'', or ''Michel de Villeneuve''; 29 September 1509 or 1511 – 27 October 1553) was a Spanish the ...

was the first European to describe the function of pulmonary circulation, although his achievement was not widely recognized at the time, for a few reasons. He firstly described it in the "Manuscript of Paris" (near 1546), but this work was never published. And later he published this description, but in a theological treatise, ''Christianismi Restitutio'', not in a book on medicine. Only three copies of the book survived but these remained hidden for decades, the rest were burned shortly after its publication in 1553 because of persecution of Servetus by religious authorities. Better known discovery of pulmonary circulation was by

Vesalius Andreas Vesalius (; 31 December 1514 – 15 October 1564) was a 16th-century Flemish people, Flemish anatomist, physician, and author of one of the most influential books on human anatomy, ''De humani corporis fabrica, De Humani Corporis Fabrica ...

's successor at

Padua Padua ( ; it, Padova ; vec, Pàdova) is a city and ''comune'' in Veneto, northern Italy. Padua is on the river Bacchiglione, west of Venice. It is the capital of the province of Padua. It is also the economic and communications hub of the a ...

Realdo Colombo Matteo Realdo Colombo (c. 1515 – 1559) was an Italian professor of anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancie ...

, in 1559. William Harvey ( 1578-1657) Venenbild

Finally, the English physician

, a pupil of

Hieronymus Fabricius Girolamo Fabrici d'Acquapendente, also known as Girolamo Fabrizio or Hieronymus Fabricius (20 May 1533 – 21 May 1619), was a pioneering anatomist Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the na ...

(who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments and published his ''

Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus :''For other works by a similar name see De Motu (disambiguation)''. Image:William Harvey ( 1578-1657) Venenbild.jpg, An experiment from Harvey's ''Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus'' ''Exercitatio Anatomica de Motu Co ...

'' in 1628, which "demonstrated that there had to be a direct connection between the venous and arterial systems throughout the body, and not just the lungs. Most importantly, he argued that the beat of the heart produced a continuous circulation of blood through minute connections at the extremities of the body. This is a conceptual leap that was quite different from Ibn al-Nafis' refinement of the anatomy and bloodflow in the heart and lungs." This work, with its essentially correct exposition, slowly convinced the medical world. However, Harvey was not able to identify the capillary system connecting arteries and veins; these were later discovered by

Marcello Malpighi Marcello Malpighi (10 March 1628 – 30 November 1694) was an Italians, Italian biologist and physician, who is referred to as the "Founder of microscopical anatomy, histology & Father of physiology and embryology". Malpighi's name is borne by s ...

in 1661. In 1956, André Frédéric Cournand,

Werner Forssmann Werner Theodor Otto Forßmann (Forssmann in English; 29 August 1904 – 1 June 1979) was a physician A physician (American English), medical practitioner (English in the Commonwealth of Nations, Commonwealth English), medical doctor, or simp ...

and Dickinson W. Richards were awarded the

Nobel Prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel Alfred Bernhard Nobel ( , ; 21 October 1833 – 10 December 1896) was a Swedish chemist, engineer, inventor, busines ...

in Medicine "for their discoveries concerning

heart catheterization Cardiac catheterization (heart cath) is the insertion of a catheter In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, pr ...

and pathological changes in the circulatory system." In his Nobel lecture, Forssmann credits Harvey as birthing cardiology with the publication of his book in 1628. In the 1970s,

Diana McSherry Diana McSherry (born 1945) is an American computer scientist A computer scientist is a person A person (plural people or persons) is a being that has certain capacities or attributes such as reason, morality, consciousness or self-conscious ...

developed computer-based systems to create images of the circulatory system and heart without the need for surgery.

References

External links

Circulatory Pathways
in ''Anatomy and Physiology'' by OpenStax
The Circulatory System

Study on the Manuscript of Paris by Servetus (1546 description of the Pulmonary Circulation) {{DEFAULTSORT:Circulatory System Exercise physiology Angiology

Structure

Cardiovascular system

Arteries

Capillaries

Veins

Portal veins

Heart

Coronary vessels

Lungs

Systemic circulation

Brain

Kidneys

Lymphatic system

Development

Heart

Arteries

Veins

Function

Cardiovascular system

Lymphatic system

Clinical significance

Cardiovascular disease

Investigations

Surgery

Society and culture

Other animals

Open circulatory system

Closed circulatory system

No circulatory system

History

See also

References

External links