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{{About|the organ system|the band|Circulatory System|transport in plants|Vascular tissue}}
{{Infobox Anatomy |
Name         = Circulatory system |
Latin        = systema cardiovasculare |
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GrayPage     = |
Image        = Circulatory System en.svg |
Caption      = The human circulatory system. Red indicates oxygenated blood, blue indicates deoxygenated. |
Image2       = |
Caption2     = |
Precursor    = |
System       = |
Artery       = |
Vein         = |
Nerve        = |
Lymph        = |
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}}
The '''circulatory system'''  is an [[organ (anatomy)|organ system]] that passes nutrients (such as [[amino acids]] and [[electrolytes]]), gases, hormones, [[blood]] cells, etc. to and  from [[cells (biology)|cells]] in the body to help fight diseases and help stabilize body temperature and [[pH]] to maintain [[homeostasis]].

This system may be seen strictly as a blood distribution network, but some consider the circulatory system as composed of the '''cardiovascular system''', which distributes blood,<ref>{{DorlandsDict|eight/000105264|cardiovascular system}}</ref> and the '''[[lymphatic system]]''',<ref>{{DorlandsDict|nine/000951445|circulatory system}}</ref> which distributes [[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 most primitive animal [[phylum|phyla]] lack circulatory systems.  The lymphatic system, on the other hand, is an open system.

Two types of fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the cardiovascular system. The lymph, lymph nodes, and lymph vessels form the [[lymphatic system]]. The cardiovascular system and the lymphatic system collectively make up the circulatory system.

==Human cardiovascular system==
The main components of the human cardiovascular system are the [[heart]] and the [[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. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, which 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.

===Pulmonary circulation===
{{Main|Pulmonary circulation}}
The Pulmonary circulation is the portion of the cardiovascular system which transports [[oxygen]]-depleted [[blood]] away from the heart, to the [[lungs]], and returns oxygenated blood back to the heart.

[[Oxygen]] deprived blood from the [[vena cava]] enters the right atrium of the heart and flows through the [[tricuspid valve]] into the right ventricle, from which it is pumped through the [[pulmonary semilunar valve]] into the pulmonary arteries which go to the lungs. Pulmonary veins return the now oxygen-rich blood to the heart, where it enters the left atrium before flowing through the [[mitral valve]] into the left ventricle. Then, oxygen-rich blood from the left ventricle is pumped out via the aorta, and on to the rest of the body.

===Systemic circulation===
{{Main|Systemic circulation}}
Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart, to the rest of the body, and returns oxygen-depleted blood back to the heart. Systemic circulation is, distance-wise, much longer than pulmonary circulation, transporting blood to every part of the body.

===Coronary circulation===
{{Main|Coronary circulation}}
The coronary circulatory system provides a blood supply to the heart.  As it provides oxygenated blood to the heart, it is by definition a part of the systemic circulatory system.

===Heart===
[[File:Diagram of the human heart (cropped).svg|300px|thumb|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.

===Closed cardiovascular system===
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 enters [[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. The heart is located in the center of the body between the two lungs. The reason that the heart beat is felt on the left side is because the left ventricle is pumping harder.

===Measurement techniques===
* [[Electrocardiogram]]—for cardiac electrophysiology
* [[Sphygmomanometer]] and [[stethoscope]]—for blood pressure
* [[Pulse meter]]—for cardiac function (heart rate, rhythm, dropped beats)
* [[Pulse]]—commonly used to determine the heart rate in absence of certain cardiac pathologies
* [[Heart rate variability]] -- used to measure variations of time intervals between heart beats
* [[Nail (anatomy)|Nail]] bed blanching test—test for perfusion
* Vessel [[cannula]] or [[catheter]] pressure measurement—pulmonary wedge pressure or in older animal experiments.

===Health and disease===
{{Main|Cardiovascular disease}}

{{Main|Congenital heart defect}}

===Oxygen transportation===
{{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 [[haemoglobin]] molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to Hgb. The [[haemoglobin]] molecule is the primary transporter of oxygen in [[mammals]] and many other species.

==Nonhuman==
=== Other vertebrates ===

The circulatory systems of all [[vertebrate]]s, as well as of [[annelid]]s (for example, [[earthworm]]s) and [[cephalopod]]s ([[squid]] and [[octopus]]) 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 that the four-chambered heart of birds evolved independently from that of mammals.

===Open circulatory system===
The Open Circulatory System is a system in which fluid (called [[hemolymph]]) 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. 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]].

===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 jellies, 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 of discovery==
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 traveled to every member through the arteries.  Although this concept of the circulatory system is greatly flawed, 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 - History of anatomy]</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>{{citation|title=Vasovagal syncope in the Canon of Avicenna: The first mention of carotid artery hypersensitivity|last=Mohammadali M. Shojaa, R. Shane Tubbsb, Marios Loukasc|first=Majid Khalilid, Farid Alakbarlie, Aaron A. Cohen-Gadola|journal=International Journal of Cardiology|volume=134|issue=3|date=29 May 2009|publisher=[[Elsevier]]|doi=10.1016/j.ijcard.2009.02.035|pages=297–301|pmid=19332359|last2=Tubbs|first2=RS|last3=Loukas|first3=M|last4=Khalili|first4=M|last5=Alakbarli|first5=F|last6=Cohen-Gadol|first6=AA}}</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>Rachel Hajar (1999), "The Greco-Islamic Pulse", ''Heart Views'' '''1''' (4): 136-140 [138]</ref>{{Verify source|date=September 2010}}

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>Chairman's Reflections (2004), "[http://www.hmc.org.qa/heartviews/VOL5NO2/special_section.htm Traditional Medicine Among Gulf Arabs, Part II: Blood-letting]", ''Heart Views'' '''5''' (2), p. 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>{{citation|title=Ibn al-Nafis, the pulmonary circulation, and the Islamic Golden Age|first=John B.|last=West|journal=Journal of Applied Physiology|volume=105|pages=1877–80|date=October 9, 2008|doi=10.1152/japplphysiol.91171.2008|pmid=18845773|issue=6|pmc=2612469}}</ref> Ibn al-Nafis' theory, however, was confined to blood transit in the lungs and did not extend to the entire body.

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>Peter E. Pormann and E. Savage Smith, ''Medieval Islamic medicine'' Georgetown University, Washington DC, 2007, p. 48.</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.

==Other images==
<gallery>
File:Blutkreislauf.png
File:Circulatory_System_en.png|More accurate drawing
</gallery>

==See also==
<div style="-moz-column-count:3; column-count:3;">
*[[Microcirculation]]
* [[Cardiology]]
* [[Lymphatic system]]
* [[Blood vessels]]
* [[Innate heat]]
* [[Cardiac muscle]]
* [[Major systems of the human body]]
* [[Heart]]
* [[Amato Lusitano]]
* [[William Harvey]]
</div>

==References==
{{Reflist}}

==External links==
* [http://www.healthmean.com/bodysystems/the-circulatory-system/ The Circulatory System Article]
* [http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookcircSYS.html The Circulatory System], a comprehensive overview
* [http://www.nature.com/ncpcardio/index.html NCP Cardiovascular Medicine] A Journal Covering Clinical Cardiovascular Medicine

{{organ_systems}}

{{Heart}}
{{Arteries and veins}}

{{Cardiovascular physiology}}

{{Development of circulatory system}}

{{Circulatory system pathology}}

{{Lymphatic flow}}

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