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{{About|the organ system|transport in plants|Vascular tissue}}
{{merge from|Systemic circulation|discuss=Talk:Circulatory system#Proposed merge with Systemic circulation|date=December 2014}}
{{Infobox anatomy
| Name = Circulatory system
| Latin = systema cardiovasculare
| GraySubject =
| GrayPage =
| Image = Circulatory System en.svg
| Caption = The human circulatory system (simplified). Red indicates oxygenated blood carried in [[artery|arteries]], blue indicates deoxygenated blood carried in [[vein]]s. [[Capillary|Capillaries]], which join the arteries and veins, and the [[lymphatic system]] are not shown.
| Image2 =
| Caption2 =
| Precursor =
| System =
| Artery =
| Vein =
| Nerve =
| Lymph =
| MeshName =
| MeshNumber =
}}
The '''circulatory system''', also called the '''cardiovascular system''', is an [[Biological system|organ system]] that permits [[blood]] to circulate and transport nutrients (such as [[amino acids]] and [[electrolytes]]), [[oxygen]], [[carbon dioxide]], [[hormone]]s, and [[blood]] cells to and from [[Cell (biology)|cells]] in the body to nourish it and help to fight diseases, stabilize [[Thermoregulation|body temperature]] and [[pH]], and to maintain [[homeostasis]]. The study of [[blood flow]] is called [[hemodynamics]].

The circulatory system is often seen to comprise both the '''cardiovascular system''', which distributes blood, and the '''[[lymphatic system]]''', which circulates [[lymph]].<ref name="ReferenceA">{{DorlandsDict|nine/000951445|circulatory system}}</ref> These are two separate systems. The passage of lymph for example takes a lot longer than that of blood.<ref>http://www.cancerresearch.uk</ref> Blood is a fluid consisting of [[blood plasma|plasma]], [[red blood cell]]s, [[white blood cell]]s, and [[platelets]] that is circulated by the [[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 [[capillary filtration|filtered]] from the [[interstitial fluid]] (between cells) and returned to the lymphatic system. The cardiovascular (from Latin words meaning 'heart'-'vessel') system comprises the blood, [[heart]], and [[blood vessel]]s.<ref>{{DorlandsDict|eight/000105264|cardiovascular system}}</ref> The lymph, [[lymph node]]s, and [[lymphatic vessel|lymph vessels]] form the lymphatic system, which returns filtered blood plasma from the interstitial fluid (between cells) as lymph.

While humans, as well as other [[vertebrates]], have a closed cardiovascular system (meaning that the blood never leaves the network of [[arteries]], [[veins]] and [[capillaries]]), some [[invertebrate]] groups have an open cardiovascular system. The lymphatic system, on the other hand, is an open system providing an accessory route for excess interstitial fluid to get returned to the blood.<ref>{{cite book|author=Sherwood, Lauralee |title=Human Physiology: From Cells to Systems |url=http://books.google.com/books?id=I9qH3eZ1pP0C&pg=PT401 |year=2011 |publisher=Cengage Learning |isbn=978-1-133-10893-1 |pages=401–}}</ref> The more primitive, [[diploblastic]] animal [[phylum|phyla]] lack circulatory systems.

==Structure==

===Cardiovascular system===
{{anchor|Human cardiovascular system}}
{{multiple image|align=right|image1=Vein_art_near.png|width1=235|image2=Artery.png|width2=250|caption1=Depiction of the heart, major veins and arteries constructed from body scans.|caption2=Cross section of a human artery}}

The essential components of the human cardiovascular system are the [[heart]], [[blood]], and [[blood vessel]]s. <ref>{{MeshName|Cardiovascular+System}}</ref> It includes: the [[pulmonary circulation]], a "loop" through the [[lung]]s where blood is oxygenated; and the [[systemic circulation]], a "loop" through the rest of the body to provide [[oxygenate]]d blood. The systemic circulation can also be seen to function in 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.<ref>{{cite web|last=Pratt|first=Rebecca|title=Cardiovascular System: Blood|url=https://app.anatomyone.com/systemic/cardiovascular-system/blood|work=AnatomyOne|publisher=Amirsys, Inc.}}</ref> Blood consists of [[blood plasma|plasma]], [[red blood cells]], [[white blood cells]], and [[platelets]]. Also, the [[digestive system]] works with the circulatory system to provide the nutrients the system needs to keep the [[heart]] pumping.<ref name="Guyton">{{cite book|title=Guyton Textbook of Medical Physiology|edition=10|author=Guyton, Arthur and Hall, John |year=2000|isbn= 072168677X}}</ref>

The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of [[blood vessels]]. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enter [[interstitial fluid]], 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]], is not closed.

====Heart====
[[File:Diagram of the human heart (cropped).svg|250px|thumb|left|View from the front, which means the right side of the heart is on the left of the diagram (and vice versa)]]
{{Main|Heart}}
The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human [[heart]] there is one [[atrium (heart)|atrium]] and one [[Ventricle (heart)|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.

The [[coronary circulation]] system provides a blood supply to the [[myocardium|heart muscle]] itself. The coronary circulation begins near the origin of the [[aorta]] by two 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. Back flow of blood through its opening during [[atrial systole]] is prevented by the [[Thebesian valve]]. The [[smallest cardiac veins]] drain directly into the heart chambers.<ref name="Guyton"/>

====Lungs====
<!--[[File:Blausen 0168 CardiovascularSystem.png|thumb|Circulation showing pulmonary and systemic circuits.]]-->
[[File:2119 Pulmonary Circuit.jpg|thumb|370px|right|The pulmonary circulation as it passes from the heart. Showing both the [[pulmonary artery]] and [[bronchial artery|bronchial arteries]].]]
{{Main|Pulmonary circulation}}
The [[pulmonary circulation|circulatory system of the lungs]] 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]] into the pulmonary artery to the lungs. Gas exchange occurs in the lungs, whereby {{CO2|link=yes}} is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now oxygen-rich blood to the [[left atrium]].<ref name="Guyton"/>

A separate system known as the [[bronchial circulation]] supplies blood to the tissue of the larger airways of the lung.

====Systemic circulation====
{{Main|Systemic circulation}}
The [[systemic circulation]] is the circulation of the blood to all parts of the body except the lungs. 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.<ref name="Guyton"/>

====Brain====
{{Main|Cerebral circulation}}
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 artery|internal carotid arteries]] and supplies the front of the brain. The posterior circulation arises from the [[vertebral artery|vertebral arteries]], and supplies the back of the brain and [[brainstem]]. The circulation from the front and the back join together ([[anastomise]]) at the [[Circle of Willis]].

====Kidneys====
The [[renal circulation]] receives around 20% of the cardiac output. It branches from the [[abdominal aorta]] and returns blood to the ascending [[vena cava]]. It is the blood supply to the [[kidney]]s, and contains many specialized blood vessels.

===Lymphatic system===
The [[lymphatic system]] is part of the circulatory system. It is comprised of a network of [[lymphatic vessel]]s and [[lymph capillaries]] , [[lymph nodes]] and [[lymphatic organs|organs]], and [[lymphatic tissues]] and circulating [[lymph]]. One of its major functions is to carry the lymph, draining and returning [[interstitial fluid]] back towards the heart for return to the cardiovascular system, by emptying into the [[lymphatic duct]]s. Its other main function is involved in the [[immune system]].

===Physiology===
[[File:Erytrocyte deoxy to oxy v0.7.gif|thumb|An animation of a typical human red blood cell cycle in the circulatory system. This animation occurs at real time (20 seconds of cycle) and shows the red blood cell deform as it enters capillaries, as well as changing color as it alternates in states of oxygenation along the circulatory system.]]
{{Main|Blood#Oxygen transport}}
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 [[mammal]]s and many other species.

==Development==
{{Main|Fetal circulation}}

The development of the circulatory system starts with [[vasculogenesis]] in the [[embryo]]. 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 which develop on the upper part of the embryo. The venous system arises from three bilateral veins during weeks 4&nbsp;– 8 of [[Human embryogenesis|embryogenesis]]. [[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]]s) from the mother through the [[placenta]] and the [[umbilical cord]].<ref name="Whitaker">{{cite book |last=Whitaker |first=Kent |chapter=Fetal Circulation |chapterurl=http://books.google.com/books?id=R3WK8XyAHYgC&pg=PA18 |title=Comprehensive Perinatal and Pediatric Respiratory Care |publisher=Delmar Thomson Learning |year=2001 |isbn=978-0-7668-1373-1 |pages=18–20}}</ref>

===Arterial development===
{{Main|Aortic arches}}
The human arterial system originates from the aortic arches and from the [[dorsal aortae]] starting from week 4 of embryonic life. The first and second aortic arches regress and forms only the [[maxillary artery|maxillary arteries]] and [[stapedial artery|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 [[:wikt:dorsal|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]], 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|suprarrenal]] 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]].

===Venous development===

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

==Clinical significance==
{{anchor|Health and disease}}
Many diseases affect the circulatory system. This includes [[cardiovascular disease]], affecting the cardiovascular system, and [[lymphatic disease]] affecting the lymphatic system. [[Cardiologist]]s are medical professionals which specialise in the heart, and [[cardiothoracic surgeon]]s specialise in operating on the heart and its surrounding areas. [[Vascular surgeon]]s are surgeons which focus on other parts of the circulatory system

===Cardiovascular disease===
{{Main|Cardiovascular disease}}
Diseases affecting the cardiovascular system are called [[cardiovascular disease]].

Many of these diseases are called "[[lifestyle disease]]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 [[fibrofatty plaque]]s 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]]s, which are diseases which 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 attack]]s, 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 variation]]s.

===Measurement techniques===
[[File:Arteria-lusoria MRA MIP.gif|thumb|[[Magnetic resonance angiography]] of [[aberrant subclavian artery]]]]
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]] through a [[sphygmomanometer]] or the use of a [[stethoscope]] to listen to the heart for [[cardiac murmur|murmur]]s 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 pressure]]s. 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 [[stent]]s, and active bleeds may be managed by the insertion of coils. An MRI may be used to image arteries, called an [[MRI angiogram]]. For evaluation of the blood supply to the lungs a [[CT pulmonary angiogram]] may be used.

[[Ultrasound]] can also be used, particularly to identify the health of veins, and a [[carotid doppler ultrasound]] or [[venous doppler ultrasound]] can be used to evaluate for narrowing of the [[carotid arteries]] or thrombus formation in the legs, respectively.

===Surgery===
{{expand section|date=March 2015}}
* Cardiac arterial bypass grafts
* Stent insertion
* Arterial grafting
* Vein stripping
* Cosmetic procedures

==Society and culture==
{{expand section|date=March 2015}}
A number of [[alternate medical system]]s such as [[Chinese medicine]] view the circulatory system in different ways.

==Other animals==
{{multiple image
| align = right
| direction = vertical
| width = 220
| header = Circulation in vertebrates
| header_align = center
| header_background =
| footer =
| footer_align = <!-- left/right/center -->
| footer_background =
| background color =
| image1 = Evolution BV system.svg
| alt1 =
| caption1 = {{center|''Fish, amphibians and mammals''}}'''1''': heart{{right|{{bg|#000066|&nbsp; &nbsp;}} venous blood &nbsp;}}<br />'''2''': [[Systemic circulation|systemic]]{{right|{{bg|#FF0000|&nbsp; &nbsp;}} arterial blood &nbsp;&nbsp;}}<br />'''3''': [[Pulmonary circulation|pulmonary]]{{right|{{bg|#00CCFF|&nbsp; &nbsp;}} mixed blood &nbsp; &nbsp;}}
}}

===Other vertebrates===
[[File:Two chamber heart.svg|thumb|left|Two-chambered heart of a fish]]

The circulatory systems of all [[vertebrate]]s, as well as of [[annelid]]s (for example, [[earthworm]]s) and [[cephalopod]]s ([[squid]]s, [[octopus]]es and relatives) are ''closed'', just as in humans. Still, the systems of [[fish]], [[amphibian]]s, [[reptile]]s, and [[bird]]s show various stages of the [[evolution]] of the circulatory system.

In fish, the system has only one circuit, with the blood being pumped through the capillaries of the [[gill]]s and on to the capillaries of the body tissues. This is known as ''single cycle'' circulation. The heart of fish is, therefore, only a single pump (consisting of two chambers).

In amphibians and most reptiles, a [[double circulatory system]] is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.

In reptiles, the [[ventricular septum]] of the heart is incomplete and the [[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]] 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.

Birds and mammals show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought{{Citation needed|date=August 2011}} that the four-chambered heart of birds evolved independently from that of mammals.

===Open circulatory system===
{{See also|Hemolymph}}
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 and there is no distinction between [[blood]] and [[interstitial fluid]]; this combined fluid is called [[hemolymph]] or haemolymph.<ref>{{cite web|last=Bailey|first=Regina|title=Circulatory System|url=http://biology.about.com/od/organsystems/a/circulatorysystem.htm|work=biology.about.com}}</ref> 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]] 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 [[cell (biology)|cell]]s. Hemolymph is composed of [[water]], [[inorganic chemistry|inorganic]] [[Salt (chemistry)|salt]]s (mostly [[Sodium|Na<sup>+</sup>]], [[Chlorine|Cl<sup>−</sup>]], [[Potassium|K<sup>+</sup>]], [[Magnesium|Mg<sup>2+</sup>]], and [[Calcium|Ca<sup>2+</sup>]]), and [[organic chemistry|organic compounds]] (mostly [[carbohydrate]]s, [[protein]]s, and [[lipid]]s). The primary oxygen transporter molecule is [[hemocyanin]].

There are free-floating cells, the [[hemocyte]]s, within the hemolymph. They play a role in the arthropod [[immune system]].

[[File:Pseudoceros bifurcus - Blue Pseudoceros Flatworm.jpg|thumb|left|Flatworms, such as this ''[[Pseudoceros bifurcus]]'', lack specialized circulatory organs]]

===Absence of circulatory system===
Circulatory systems are absent in some animals, including [[flatworms]] (phylum [[Platyhelminthes]]). Their [[body cavity]] has no lining or enclosed fluid. Instead a muscular [[pharynx]] leads to an extensively branched [[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]] 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.

{{clear}}

==History==
[[File:Charta ex qva figvram parare convenit, illi qvae nervorvm seriem exprimit appendendam, 1543..JPG|thumb|right|Human anatomical chart of blood vessels, with heart, lungs, liver and kidneys included. Other organs are numbered and arranged around it. Before cutting out the figures on this page, Vesalius suggests that readers glue the page onto parchment and gives instructions on how to assemble the pieces and paste the multilayered figure onto a base "muscle man" illustration. "Epitome", fol.14a. HMD Collection, WZ 240 V575dhZ 1543.]]
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]].<ref name=Dwivedi&Dwivedi07/> He also seems to have possessed knowledge of the [[arteries]], described as 'channels' by Dwivedi & Dwivedi (2007).<ref name=Dwivedi&Dwivedi07>Dwivedi, Girish & Dwivedi, Shridhar (2007). [http://medind.nic.in/iae/t07/i4/iaet07i4p243.pdf ''History of Medicine: Sushruta&nbsp;– the Clinician&nbsp;– Teacher par Excellence'']. [[National Informatics Centre|National Informatics Centre (Government of India)]].</ref> 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 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.<ref>[http://www.scienceclarified.com/Al-As/Anatomy.html Anatomy&nbsp;– History of anatomy]. Scienceclarified.com. Retrieved 2013-09-15.</ref>

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 cycle]]s and valvular function", and "had a vision of blood circulation" in his ''Treatise on Pulse''.<ref>{{cite pmid|19332359}}</ref>{{Verify source|date=September 2010}} 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."<ref name=Hajar>{{cite journal|author=Hajar, Rachel |year=1999|title=The Greco-Islamic Pulse|journal=Heart Views|volume=1|issue=4|pages=136–140 [138]|url=http://www.arjournals.info/jourarticle.php?art_id=20237}}</ref>

In 1242, the [[Medicine in medieval Islam|Arabian physician]], [[Ibn al-Nafis]], became the first person to accurately describe the process of [[pulmonary circulation]], for which he is sometimes considered the father of [[Cardiovascular physiology|circulatory physiology]].<ref>{{cite journal | last1 = Reflections | first1 = Chairman's | year = 2004 | title = Traditional Medicine Among Gulf Arabs, Part II: Blood-letting | url =http://www.hmc.org.qa/heartviews/VOL5NO2/special_section.htm | journal = Heart Views | volume = 5 | issue = 2| pages = 74–85 [80] }}</ref>{{Failed verification|date=June 2010}} Ibn al-Nafis stated in his ''Commentary on Anatomy in Avicenna's Canon'':

<blockquote>"...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..."</blockquote>

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.<ref>{{cite pmid|18845773}}</ref> 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"<ref>Gonzalez Etxeberria, Patxi (2011) ''Amor a la verdad, el&nbsp;– vida y obra de Miguel servet'' [''The love for truth. Life and work of Michael Servetus'']. Navarro y Navarro, Zaragoza, collaboration with the Government of Navarra, Department of Institutional Relations and Education of the Government of Navarra. ISBN 8423532666 pp. 215–228 & 62nd illustration (XLVII)</ref><ref>[http://www.michaelservetusresearch.com/ENGLISH/works.html Michael Servetus Research] Study with graphical proof on the Manuscript of Paris and many other manuscripts and new works by Servetus</ref> (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, the rest were burned shortly after its publication in 1553 because of persecution of Servetus by religious authorities. Better known was its discovery by [[Vesalius]]'s successor at [[University of Padua|Padua]], [[Realdo Colombo]], in 1559.

[[File:William Harvey ( 1578-1657) Venenbild.jpg|thumb|Image of veins from [[William Harvey]]'s ''Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus'']]
Finally, [[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 ''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."<ref>Pormann, Peter E. and Smith, E. Savage (2007) ''Medieval Islamic medicine'' Georgetown University, Washington DC, p. 48, ISBN 1589011619.</ref> 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."<ref>
{{cite web
| url = http://nobelprize.org/nobel_prizes/medicine/laureates/1956/index.html
| title = The Nobel Prize in Physiology or Medicine 1956
| accessdate = 2007-07-28
| publisher = Nobel Foundation
}}</ref>

==See also==
{{colbegin||30em}}
* [[Cardiology]]
* [[Innate heat]]
* [[Cardiac muscle]]
* [[Major systems of the human body]]
* [[Amato Lusitano]]
* [[Double circulatory system]]
{{colend}}

==References==
{{Reflist|35em}}

==External links==
{{Sister project links | wikt=Circulatory system | commons=Category:Circulatory system display=Circulatory system }}

{{Library resources box
| by = no
| onlinebooks = no
| others = no
| about = yes
| label = Circulatory system}}
*http://cnx.org/content/m46646/latest/
*[http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookcircSYS.html The Circulatory System]
*Reiber C. L. & McGaw I. J. (2009). "A Review of the "Open" and "Closed" Circulatory Systems: New Terminology for Complex Invertebrate Circulatory Systems in Light of Current Findings". ''[[International Journal of Zoology]]'' '''2009''': 8 pages. {{doi|10.1155/2009/301284}}.
*Patwardhan K. [http://advan.physiology.org/content/36/2/77.long The history of the discovery of blood circulation: unrecognized contributions of Ayurveda masters]. Adv Physiol Educ. 2012 Jun;36(2):77–82.
*[http://www.michaelservetusresearch.com/ENGLISH/works.html Michael Servetus Research] Study on the Manuscript of Paris by Servetus (1546 description of the Pulmonary Circulation)


{{Heart anatomy}}
{{Arteries and veins}}
{{Cardiovascular physiology}}
{{Development of circulatory system}}
{{Circulatory system pathology}}

{{DEFAULTSORT:Circulatory System}}
[[Category:Circulatory system| ]]
[[Category:Exercise physiology]]

Revision as of 21:49, 30 March 2015

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