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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 ...

amino acids
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 resis ...
),
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 ...

carbon dioxide
,
hormone A hormone (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 country located in Southeast Europe. Its population is appr ...

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 ...

blood cell
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
pH
pH
, and 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 ...
. 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 ...

lymphatic system
, 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 language, Greek ''erythros'' for "red" and ''k ...

red blood cell
s,
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. ...

platelets
that is circulated by 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
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 An organ system is a biological system A biological system is a comp ...
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 ...

lymph node
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 A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...

vertebrates
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 ...

capillaries
), 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 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 ...
, 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
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
,
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
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. 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 ...

microcirculation
. 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
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 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
,
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 ...
, 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. ...

platelets
. Also, 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
works with the circulatory system to provide the nutrients the system needs to keep 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
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 co ...

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

lymphatic system
, 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 muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the Unite ...
, through the
aortic semilunar valve
aortic semilunar valve
. The first part of the systemic circulation is the
aorta The aorta ( ) is the main and largest artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vas ...

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, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mas ...

blood pressure
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 in the microcirculation that extends and branches out from an artery and leads to capillary, capillaries. Arterioles have muscle, muscular walls (usually only one to two layers of smooth muscle) and a ...

arteriole
s and then into the
capillaries 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 An organ system is a biologic ...

capillaries
. 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 The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulat ...
s, which merge into
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
. 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 ...

inferior vena cava
– 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 ventricles of the heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood ...
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
.


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 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 ...
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 The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An ...
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
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
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 ...
,
left ventricle A ventricle is one of two large chambers toward the bottom 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 Unite ...
,
right atrium The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the ventricles of the heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood ...
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 bloo ...
. 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 ...

heart muscle
itself. The coronary circulation begins near the origin of the
aorta The aorta ( ) is the main and largest artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vas ...

aorta
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 ...

coronary arteries
: 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 The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system ...
drain directly into the heart chambers.


Lungs

The circulatory system of the lungs is the portion of the cardiovascular system in which
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
-depleted
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
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 ...

pulmonary artery
, 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 liqui ...

Gas exchange
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
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 ...
. 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 ...

internal carotid arteries
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 ...

vertebral arteries
, 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 anim ...

brainstem
. 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 ...

Circle of Willis
.


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 ...

abdominal aorta
and returns blood to the ascending
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 ...
. 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
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 ...

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

embryogenesis
.
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 ...

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

placenta
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
aorta The aorta ( ) is the main and largest artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vas ...

aorta
itself. Approximately thirty smaller arteries branch from this at the back and sides. These branches form the intercostal arteries, 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 artery, renal, Inferior suprarenal artery, suprarenal and Gonadal artery, gonadal arteries. Finally, branches at the front of the aorta consist of the vitelline arteries and umbilical arteries. The vitelline arteries form the Celiac artery, celiac, Superior mesenteric artery, superior and Inferior mesenteric artery, inferior mesenteric arteries of the gastrointestinal tract. After birth, the umbilical arteries will form the Internal iliac artery, internal iliac arteries.


Veins

The human venous system develops mainly from the vitelline veins, the umbilical veins and the Posterior cardinal vein, cardinal veins, all of which empty into the sinus venosus.


Function


Cardiovascular system

About 98.5% of the
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
in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with hemoglobin 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 mammals and many other species.


Lymphatic system


Clinical significance

Many diseases affect the circulatory system. These include a number of
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve 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 ...
s, affecting the cardiovascular system, and lymphatic diseases 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.


Cardiovascular disease

Diseases affecting the cardiovascular system are called
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve 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 ...
. Many of these diseases are called "lifestyle diseases" 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 is the precursor to many of these diseases. It is where small Atheroma, atheromatous plaques 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 syndromes, 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 formation or splitting ("dissection") of arteries. Another major cardiovascular disease involves the creation of a Thrombus, clot, called a "thrombus". These can originate in veins or arteries. Deep venous thrombosis, 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 Embolus, embolise, meaning travel to another location in the body. The results of this may include pulmonary embolus, transient ischaemic attacks, or stroke. Cardiovascular diseases may also be congenital in nature, such as Congenital heart defect, heart defects 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 variations.


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 as an indicator of a person's heart rate, the taking of
blood pressure Blood pressure (BP) is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mas ...

blood pressure
through a sphygmomanometer or the use of a stethoscope to listen to the heart for cardiac murmur, murmurs which may indicate problems with the heart valve, heart's valves. An electrocardiogram 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 or catheter inserted into an artery may be used to measure pulse pressure or pulmonary wedge pressures. Angiography, which involves injecting a dye into an artery to visualise an arterial tree, can be used in the heart (coronary angiography) or brain. At the same time as the arteries are visualised, blockages or narrowings may be fixed through the insertion of stents, and active bleeds may be managed by the insertion of coils. An MRI may be used to image arteries, called an magnetic resonance angiography, MRI angiogram. For evaluation of the blood supply to the lungs a CT pulmonary angiogram may be used. Medical ultrasound#Angiology (vascular), Vascular ultrasonography include for example: * Intravascular ultrasound * 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 stent used in angioplasty * Vascular surgery * Vein stripping * 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.


Other animals

While humans, as well as other
vertebrates 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 ...

vertebrates
, have a closed blood circulatory system (meaning 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 ...

capillaries
), 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 circulatory system containing a heart but limited blood vessels. The most 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 phylum, 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 evolved in an ancestral vertebrate some 540–510 million years ago.


Open circulatory system

In arthropods, 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
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
and
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, ...
; this combined fluid is called hemolymph or haemolymph. Muscular movements by the animal during Animal locomotion, locomotion can facilitate hemolymph movement, but diverting flow from one area to another is limited. When 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
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
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 ...
. Hemolymph is composed of water, Inorganic chemistry, inorganic Salt (chemistry), salts (mostly sodium, chloride, potassium, magnesium, and calcium), and Organic chemistry, organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin. There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system.


Closed circulatory system

The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squids, octopuses 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, amphibians, reptiles, and birds show various stages of the evolution 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 gills 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 of the heart is incomplete and 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 ...

pulmonary artery
is equipped with a sphincter muscle. 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
left ventricle A ventricle is one of two large chambers toward the bottom 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 Unite ...
and out through the
aorta The aorta ( ) is the main and largest artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vas ...

aorta
. 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 (cold-blooded) animals in the regulation of their body temperature. Birds, mammals, and crocodilians 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 flatworms. Their body cavity has no lining or enclosed fluid. Instead, a muscular pharynx leads to an extensively branched
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
that facilitates direct diffusion 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 can diffuse from the surrounding water into the cells, and
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
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, have more extensive branching from their gastrovascular cavity (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

The earliest known writings on the circulatory system are found in the Ebers Papyrus (16th century BCE), an Ancient Egyptian medicine, ancient Egyptian medical papyrus containing over 700 prescriptions and remedies, both physical and spiritual. In the 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 Ayurveda, Ayurvedic physician Sushruta in History of India, ancient India. He also seems to have possessed knowledge of the
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 ...
, 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, National Informatics Centre (Government of India).
The Heart valve, valves of the heart were discovered by a physician of the Hippocrates, 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 Ancient Greek Medicine, Greek physician, Herophilus, distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Greek anatomist Erasistratus 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, the Ancient Greek Medicine, Greek physician Galen 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'' by the Ancient Iranian Medicine, Persian physician, Avicenna, "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 cycles 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 Medicine in medieval Islam, Arabian physician, Ibn al-Nafis described the process of
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 ...
in greater, more accurate detail than his predecessors, though he believed, as they did, in the notion of vital spirit (pneuma), 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 ...

pulmonary artery
) 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 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 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's successor at University of Padua, Padua, Realdo Colombo, in 1559. Finally, the English physician William Harvey, a pupil of Hieronymus Fabricius (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'' 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 in 1661. In 1956, André Frédéric Cournand, Werner Forssmann and Dickinson W. Richards were awarded the List of Nobel laureates in Physiology or Medicine, Nobel Prize in Medicine "for their discoveries concerning heart catheterization 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 developed computer-based systems to create images of the circulatory system and heart without the need for surgery.


See also

* * * * * * * *


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 Circulatory system, Exercise physiology Angiology