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The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek ''kardia'' meaning ''heart'', and from Latin ''vascula'' meaning ''vessels''). The circulatory system has two divisions, a systemic circulation or circuit, and a pulmonary circulation or circuit. Some sources use the terms ''cardiovascular system'' and ''vascular system'' interchangeably with the ''circulatory system''. The network of blood vessels are the great vessels of the heart including large
elastic arteries An elastic artery (conducting artery or conduit artery) is an artery with many collagen and elastin filaments in the tunica media, which gives it the ability to stretch in response to each pulse. This elasticity also gives rise to the Windkessel ...
, and large veins; other arteries, smaller arterioles, capillaries that join with venules (small veins), and other veins. The circulatory system is closed in vertebrates, which means that the blood never leaves the network of blood vessels. Some invertebrates such as arthropods have an open circulatory system.
Diploblast Eumetazoa (), also known as diploblasts, Epitheliozoa, or Histozoa, are a proposed basal animal clade as a sister group of the Porifera (sponges). The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a ...
s such as
sponges Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...
, and comb jellies lack a circulatory system. Blood is a
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
consisting of
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
, red blood cells,
white blood cell White blood cells, also called leukocytes or leucocytes, are the cell (biology), cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and de ...
s, and
platelets Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...
that is circulated around the body carrying oxygen and
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
s to the tissues, and waste materials away. Circulated nutrients include
proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
and minerals, other components transported are gases such as oxygen, and carbon dioxide, hormones, and hemoglobin; providing nourishment, help in the immune system to fight
diseases A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that ar ...
, and in maintaining homeostasis by stabilizing temperature and natural pH. In vertebrates, complementary to the circulatory system is the
lymphatic system The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...
. This system carries excess plasma filtered from the capillaries as interstitial fluid between cells, away from the body tissues in an accessory route to return the excess fluid back to the blood circulation as lymph. The passage of lymph takes much longer than that of blood. The lymphatic system is a subsystem that is essential for the functioning of the blood circulatory system; without it the blood would become depleted of fluid. The lymphatic system works together with the immune system. Unlike the closed circulatory system, the lymphatic system is an open system. Some sources describe it as a ''secondary circulatory system''. The circulatory system can be affected by many
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...
s. Cardiologists 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 surgeons focus on disorders of the blood vessels, and lymphatic vessels.


Structure

The circulatory system includes the heart, blood vessels, and blood. The cardiovascular system in all vertebrates, consists of the heart and blood vessels. The circulatory system is further divided into two major circuits – a pulmonary circulation, and a
systemic circulation The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. The pulmonary circulation is a circuit loop from the right heart taking deoxygenated blood to the
lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
s where it is oxygenated and returned to the left heart. The systemic circulation is a circuit loop that delivers oxygenated blood from the left heart to the rest of the body, and returns deoxygenated blood back to the right heart via large veins known as the venae cavae. The systemic circulation can also be defined as two parts – a ''macrocirculation'' and a '' 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), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
,
red blood cells Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...
, white blood cells, and
platelets Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...
. The
digestive system The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...
also works with the circulatory system to provide the nutrients the system needs to keep the heart pumping. Further circulatory routes are associated, such as the
coronary circulation Coronary circulation is the circulation of blood in the blood vessels that supply the heart muscle (myocardium). Coronary arteries supply oxygenated blood to the heart muscle. Cardiac veins then drain away the blood after it has been deoxygenat ...
to the heart itself, the cerebral circulation to the brain,
renal circulation The renal circulation supplies the blood to the kidneys via the renal arteries, left and right, which branch directly from the abdominal aorta. Despite their relatively small size, the kidneys receive approximately 20% of the cardiac output. Eac ...
to the kidneys, and bronchial circulation to the bronchi in the lungs. The human circulatory system is
closed Closed may refer to: Mathematics * Closure (mathematics), a set, along with operations, for which applying those operations on members always results in a member of the set * Closed set, a set which contains all its limit points * Closed interval, ...
, meaning that the blood is contained within the
vascular network The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. Nutrients travel through tiny blood vessels of the microcirculation to reach organs. The
lymphatic system The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...
is an essential subsystem of the circulatory system consisting of a network of lymphatic vessels, lymph nodes, organs, tissues and circulating lymph. This subsystem is an open system. A major function is to carry the lymph, draining and returning interstitial fluid into the
lymphatic duct A lymph duct is a great lymphatic vessel that empties lymph into one of the subclavian veins. There are two lymph ducts in the body—the right lymphatic duct and the thoracic duct. The right lymphatic duct drains lymph from the right upper li ...
s back to the heart for return to the circulatory system. Another major function is working together with the immune system to provide defense against pathogens.


Heart

The heart pumps blood to all parts of the body providing
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
s and oxygen to every cell, and removing waste products. The left heart pumps oxygenated blood returned from the lungs to the rest of the body in the
systemic circulation The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. The right heart pumps deoxygenated blood to the lungs in the pulmonary circulation. In the human 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, left ventricle, right atrium and right ventricle. 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.


Pulmonary circulation

The pulmonary circulation is the portion of the cardiovascular system in which oxygen-depleted blood is pumped away from the heart, via the pulmonary artery, to the lungs and returned, oxygenated, to the heart via the pulmonary vein. Oxygen-deprived blood from the superior and inferior vena cava enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it is then pumped through the
pulmonary semilunar valve The pulmonary valve (sometimes referred to as the pulmonic valve) is a valve of the heart that lies between the right ventricle and the pulmonary artery and has three cusps. It is one of the four valves of the heart and one of the two semilunar va ...
into the pulmonary artery to the lungs. 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. A separate system known as the bronchial circulation supplies blood to the tissue of the larger airways of the lung.


Systemic circulation

The systemic circulation is a circuit loop that delivers oxygenated blood from the left heart to the rest of the body through the aorta. Deoxygenated blood is returned in the systemic circulation to the right heart via two large veins, the inferior vena cava and superior vena cava, where it is pumped from the right atrium into the pulmonary circulation for oxygenation. The systemic circulation can also be defined as having two parts – a macrocirculation and a microcirculation.


Blood vessels

The blood vessels of the circulatory system are the arteries,
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 and umbilical veins, both of which carry oxygenated b ...
, and capillaries. The large arteries and veins that take blood to, and away from the heart are known as the great vessels.


Arteries

Oxygenated blood enters the systemic circulation when leaving the left ventricle, via the
aortic semilunar valve The aortic valve is a valve in the heart of humans and most other animals, located between the left ventricle and the aorta. It is one of the four valves of the heart and one of the two semilunar valves, the other being the pulmonary valve. The ...
. The first part of the systemic circulation is the 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 the aorta are elastic. This elasticity helps to maintain the
blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
throughout the body. When the aorta receives almost five litres of blood from the heart, it recoils and is responsible for pulsating blood pressure. As the aorta branches into smaller arteries, their elasticity goes on decreasing and their compliance goes on increasing.


Capillaries

Arteries branch into small passages called arterioles and then into the capillaries. The capillaries merge to bring blood into the venous system.


Veins

Capillaries merge into venules, which merge into veins. The venous system feeds into the two major veins: the superior vena cava – which mainly drains tissues above the heart – and the inferior vena cava – which mainly drains tissues below the heart. These two large veins empty into the right atrium of the 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 veins are a slight exception to this. In humans the only significant example is the hepatic portal vein 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 that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...
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.


Coronary circulation

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 itself. The coronary circulation begins near the origin of the aorta by two coronary arteries: the right coronary artery and the left coronary artery. After nourishing the heart muscle, blood returns through the coronary veins into the coronary sinus and from this one into the right atrium. Backflow of blood through its opening during
atrial systole The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following ...
is prevented by the
Thebesian valve In the anatomy of the heart, the valve of the coronary sinus (also called the Thebesian valve, after Adam Christian Thebesius) is a semicircular fold of the lining membrane of the right atrium, at the orifice of the coronary sinus. It is situate ...
. The
smallest cardiac veins In the anatomy of the heart, the smallest cardiac veins, also known as the Thebesian veins (for Adam Christian Thebesius), are small valveless veins in the walls of all four heart chambers. Structure Course The smallest cardiac veins are mo ...
drain directly into the heart chambers.


Cerebral circulation

The brain has a dual blood supply, an ''anterior'' and a ''posterior circulation'' from arteries at its front and back. The anterior circulation arises from the internal carotid arteries to supply the front of the brain. The posterior circulation arises from the vertebral arteries, to supply the back of the brain and
brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
. The circulation from the front and the back join (
anastomise An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be norma ...
) at the circle of Willis.


Renal circulation

The
renal circulation The renal circulation supplies the blood to the kidneys via the renal arteries, left and right, which branch directly from the abdominal aorta. Despite their relatively small size, the kidneys receive approximately 20% of the cardiac output. Eac ...
is the blood supply to the kidneys, contains many specialized blood vessels and receives around 20% of the cardiac output. It branches from the
abdominal aorta In human anatomy, 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 thoracic d ...
and returns blood to the ascending vena cava.


Development

The development of the circulatory system starts with vasculogenesis in the
embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
. The human arterial and venous systems develop from different areas in the embryo. The arterial system develops mainly from the aortic arches, 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 an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
. Fetal circulation 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 obtains oxygen (and
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
s) from the mother through the placenta and the umbilical cord.


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 paired dorsal aortae arise from aortic arches that in turn arise from the aortic sac. The primary dorsal aorta is located deep t ...
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 side of the embryo, are initially present on both sides of the embryo. They later fuse to form the basis for the aorta 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 human ...
, 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, suprarenal and gonadal arteries. Finally, branches at the front of the aorta consist of the vitelline arteries and umbilical arteries. The vitelline arteries form the celiac,
superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places *Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lake ...
and inferior mesenteric arteries of the gastrointestinal tract. After birth, the umbilical arteries will form the internal iliac arteries.


Veins

The human venous system develops mainly from the
vitelline vein The vitelline veins are veins that drain blood from the yolk sac and the gut tube during gestation. Path They run upward at first in front, and subsequently on either side of the intestinal canal. They unite on the ventral aspect of the canal. B ...
s, the umbilical veins and the cardinal veins, all of which empty into the sinus venosus.


Function

About 98.5% of the 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 vertebrates.


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 or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...
s, affecting the heart and blood vessels; hematologic diseases that affect the blood, such as anemia, and
lymphatic disease Lymphatic disease is a class of disorders which directly affect the components of the lymphatic system. Examples include Castleman's disease and lymphedema. __TOC__ Types Diseases and disorder Hodgkin's Disease/Hodgkin's Lymphoma Hodgkin lymphoma ...
s affecting the lymphatic system. Cardiologists 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 surgeons focus on the blood vessels.


Cardiovascular disease

Diseases affecting the cardiovascular system are called ''cardiovascular disease''. Many of these diseases are called "
lifestyle disease Lifestyle diseases can be defined as diseases linked with one's lifestyle. These diseases are non-communicable diseases. They are caused by lack of physical activity , unhealthy eating, alcohol, substance use disorders and smoking tobacco, wh ...
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 is the precursor to many of these diseases. It is where small
atheromatous plaques An atheroma, or atheromatous plaque, is an abnormal and reversible accumulation of material in the inner layer of an arterial wall. The material consists of mostly macrophage cells, or debris, containing lipids, calcium and a variable amount o ...
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 loca ...
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 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, 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 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 shortness of breath, chest pain particularly upon breathing ...
,
transient ischaemic attack A transient ischemic attack (TIA), commonly known as a mini-stroke, is a minor stroke whose noticeable symptoms usually end in less than an hour. TIA causes the same symptoms associated with strokes, such as weakness or numbness on one side of ...
s, or
stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
. Cardiovascular diseases may also be congenital in nature, such as heart defects or
persistent fetal circulation Persistent fetal circulation is a condition caused by a failure in the systemic circulation and pulmonary circulation to convert from the antenatal circulation pattern to the "normal" pattern. Infants experience a high mean arterial pulmonary art ...
, 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 The cardiovascular examination is a portion of the physical examination that involves evaluation of the cardiovascular system. The exact contents of the examination will vary depending on the presenting complaint but a complete examination will in ...
, 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 of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
through a sphygmomanometer or the use of a
stethoscope The stethoscope is a medical device for auscultation, or listening to internal sounds of an animal or human body. It typically has a small disc-shaped resonator that is placed against the skin, and one or two tubes connected to two earpieces. ...
to listen to the heart for murmurs which may indicate problems with the 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 Coronary () may, as shorthand in English, be used to mean: * Coronary circulation, the system of arteries and veins in mammals ** Coronary artery disease ** Coronary occlusion ** A myocardial infarction, a heart attack As adjective * Referring to ...
) 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 MRI angiogram. For evaluation of the blood supply to the lungs a CT pulmonary angiogram may be used. Vascular ultrasonography may be used to investigate vascular diseases affecting the venous system and the
arterial system An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...
including the diagnosis of
stenosis A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture). ''Stricture'' ...
, thrombosis or venous insufficiency. An
intravascular ultrasound Intravascular ultrasound (IVUS) or intravascular echocardiography is a medical imaging methodology using a specially designed catheter with a miniaturized ultrasound probe attached to the distal end of the catheter. The proximal end of the cath ...
using a catheter is also an option.


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") is a surgical procedure to treat coronary artery disease (CAD), the buildup of plaques in the arteries of the heart. It can relieve chest pai ...
* Coronary stent used in angioplasty *
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 * 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.


Other animals

While humans, as well as other vertebrates, have a closed blood circulatory system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open circulatory system containing a heart but limited blood vessels. The most primitive, diploblastic animal
phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phyl ...
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 The Bilateria or bilaterians are animals with symmetry (biology)#Bilateral symmetry, bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior ...
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 Cavity may refer to: Biology and healthcare *Body cavity, a fluid-filled space in many animals where organs typically develop **Gastrovascular cavity, the primary organ of digestion and circulation in cnidarians and flatworms *Dental cavity or too ...
called the hemocoel bathes the organs directly with oxygen and nutrients, with there being no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph. Muscular movements by the animal during locomotion can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the 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: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
. Hemolymph is composed of water, inorganic salts (mostly sodium, chloride, potassium, magnesium, and calcium), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin. There are free-floating cells, the
hemocyte A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), a ...
s, 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
annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...
s (for example, earthworms) and
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
s (
squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
s,
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...
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,
amphibian Amphibians are tetrapod, four-limbed and ectothermic 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 terres ...
s,
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, 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 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 hum ...
. 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 and out through the 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. Mammals, birds 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
flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...
s. 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 gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...
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 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 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
Ayurvedic Ayurveda () is an alternative medicine system with historical roots in the Indian subcontinent. The theory and practice of Ayurveda is pseudoscientific. Ayurveda is heavily practiced in India and Nepal, where around 80% of the population rep ...
physician
Sushruta Sushruta, or ''Suśruta'' (Sanskrit: सुश्रुत, IAST: , ) was an ancient Indian physician. The ''Sushruta Samhita'' (''Sushruta's Compendium''), a treatise ascribed to him, is one of the most important surviving ancient treatises on ...
in ancient India. He also seems to have possessed knowledge of the arteries, 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 A heart valve is a Check valve, one-way valve that allows blood flow, blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow thro ...
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, 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 enters between veins and arteries by very small vessels. Thus he apparently postulated capillaries but with reversed flow of blood. In 2nd-century AD Rome, the 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 Persian physician,
Avicenna Ibn Sina ( fa, ابن سینا; 980 – June 1037 CE), commonly known in the West as Avicenna (), was a Persian polymath who is regarded as one of the most significant physicians, astronomers, philosophers, and writers of the Islamic G ...
, "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 Arabian physician, Ibn al-Nafis described the process of pulmonary circulation 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) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa ( pulmonary vein) 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. A better known discovery of pulmonary circulation was by Vesalius's successor at Padua,
Realdo Colombo Matteo Realdo Colombo (c. 1515 – 1559) was an Italian professor of anatomy and a surgeon at the University of Padua between 1544 and 1559. Early life and education Matteo Realdo Colombo or Realdus Columbus, was born in Cremona, Lombardy, the ...
, in 1559. Finally, the English physician William Harvey, 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 and surgeon known in medical science as "The Father of Embryology." Life and accomplishments ...
(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 ''Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus'' (Latin, 'An Anatomical Exercise on the Motion of the Heart and Blood in Living Beings'), commonly called ''De Motu Cordis'', is the best-known work of the physician William Harv ...
'' 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 André Frédéric Cournand (September 24, 1895 – February 19, 1988) was a French-American physician and physiologist. Biography Cournand was awarded the Nobel Prize in Physiology or Medicine in 1956 along with Werner Forssmann and Dickinson W ...
,
Werner Forssmann Werner Theodor Otto Forßmann (Forssmann in English; ; 29 August 1904 – 1 June 1979) was a German researcher and physician from Germany who shared the 1956 Nobel Prize in Medicine (with Andre Frederic Cournand and Dickinson W. Richards) for ...
and
Dickinson W. Richards Dickinson Woodruff Richards, Jr. (October 30, 1895 – February 23, 1973) was an American physician and physiologist. He was a co-recipient of the Nobel Prize in Physiology or Medicine in 1956 with André Cournand and Werner Forssmann for the de ...
were awarded the Nobel Prize in Medicine "for their discoveries concerning
heart catheterization Cardiac catheterization (heart cath) is the insertion of a catheter into a chamber or vessel of the heart. This is done both for diagnostic and interventional purposes. A common example of cardiac catheterization is coronary catheterization that ...
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 and biophysicist. She is known for her research in and development of computer-based systems to analyze heart function. Her system produced computer images of the circulation system and ...
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 Exercise physiology Angiology