Editing Circulatory system (section)

==Structure==
{{anchor|Human cardiovascular system}}
[[File:2101 Blood Flow Through the Heart.jpg|thumb|350px|Blood flow in the pulmonary and systemic circulations showing capillary networks in the torso sections]]
The circulatory system includes the [[heart]], [[blood vessel]]s, and [[blood]].<ref name="Saladin2"/> 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]].<ref>{{MeshName|Cardiovascular+System}}</ref><ref name="Hall"/><ref name="Saladin3">{{cite book |last1=Saladin |first1=Kenneth S. |title=Human anatomy |date=2011 |publisher=McGraw-Hill |location=New York |isbn=9780071222075 |page=540 |edition=3rd}}</ref> The pulmonary circulation is a circuit loop from the [[right heart]] taking deoxygenated blood to the [[lung]]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 [[Great vessels|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.<ref>{{cite web|last=Pratt|first=Rebecca|title=Cardiovascular System: Blood|url=https://app.anatomyone.com/systemic/cardiovascular-system/blood|archive-url=https://web.archive.org/web/20170224023239/https://app.anatomyone.com/systemic/cardiovascular-system/blood|url-status=dead|archive-date=2017-02-24|work=AnatomyOne|publisher=Amirsys, Inc.}}</ref> Blood consists of [[Blood plasma|plasma]], [[red blood cells]], [[white blood cells]], and [[platelets]]. The [[digestive system]] also 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|author1=Guyton, Arthur  |author2=Hall, John |year=2000|publisher=Saunders |isbn= 978-0-7216-8677-6}}</ref>

Further circulatory routes are associated, such as the [[coronary circulation]] to the heart itself, the [[cerebral circulation]] to the [[brain]], [[renal circulation]] to the [[kidney]]s, and [[bronchial circulation]] to the [[bronchi]] in the lungs.
The human circulatory system is [[closed circulatory system|closed]], meaning that the blood is contained within the [[blood vessels|vascular network]].<ref name="Lawton">{{cite book|url=https://books.google.com/books?id=mj4mEAAAQBAJ&pg=PA6|title=The Human Circulatory System|publisher=Cavendish Square Publishing|author=Lawton, Cassie M.|year=2019|page=6|isbn=978-1-50-265720-6|access-date=2022-01-28|archive-date=2022-01-28|archive-url=https://web.archive.org/web/20220128204010/https://books.google.com/books?id=mj4mEAAAQBAJ&pg=PA6|url-status=live}}</ref> Nutrients travel through tiny blood vessels of the microcirculation to reach organs.<ref name="Lawton"/> The [[lymphatic system]] is an essential subsystem of the circulatory system consisting of a network of [[lymphatic vessel]]s, [[lymph nodes]], [[lymphatic organs|organs]], [[lymphatic tissues|tissues]] and circulating [[lymph]]. This subsystem is an [[open circulatory system|open system]].<ref name="Gartner">{{cite book|url=https://books.google.com/books?id=pGTtd5i2fR8C&pg=PA166|title=Concise Histology E-Book|publisher=Elsevier Health Sciences|author1=Gartner, Leslie P.|author2=Hiatt, James L.|year=2010|page=166|isbn=978-1-43-773579-6|access-date=2022-01-28|archive-date=2022-01-28|archive-url=https://web.archive.org/web/20220128204011/https://books.google.com/books?id=pGTtd5i2fR8C&pg=PA166|url-status=live}}</ref> A major function is to carry the lymph, draining and returning [[interstitial fluid]] into the [[lymphatic duct]]s back to the heart for return to the circulatory system. Another [[Lymphatic system#Function|major function]] is working together with the [[immune system]] to provide defense against [[pathogen]]s.<ref name=Alberts>{{cite book |last1=Alberts |first1=B. |last2=Johnson |first2=A. |last3=Lewis |first3=J. |last4=Raff |first4=M. |last5=Roberts |first5=K. |last6=Walters |first6=P. |title=Molecular Biology of the Cell |edition=4th |publisher=Garland Science |year=2002 |location=New York and London |url=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=mboc4.TOC&depth=2 |isbn=978-0-8153-3218-3 |access-date=2017-08-30 |archive-date=2006-08-17 |archive-url=https://www.webcitation.org/5IDSbXuy2?url=http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC |url-status=live }}</ref>

===Heart===
{{Main|Heart}}
[[File:Blood oxygenation to the pulmonary and systemic circulation.svg|thumb|Diagram of the human [[heart]] showing blood oxygenation to the pulmonary and systemic circulation|border]]
The heart pumps blood to all parts of the body providing [[nutrient]]s and [[oxygen]] to every [[Cell (biology)|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 right heart pumps deoxygenated blood to the lungs in the [[pulmonary circulation]]. 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.

====Pulmonary circulation====
{{Main|Pulmonary circulation}}
[[File:2119 Pulmonary Circuit.jpg|thumb|370px|right|The [[pulmonary circulation]] as it passes from the [[heart]]. Showing both the [[Pulmonary artery|pulmonary]] and [[Bronchial artery|bronchial arteries]].]]
The pulmonary circulation is the part of the circulatory system in which [[Deoxygenated blood|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 circuit from the systemic circulation, the [[bronchial circulation]] supplies blood to the tissue of the larger airways of the lung.

====Systemic circulation====
[[File:2105 Capillary Bed.jpg|thumb|upright=1.4|Capillary bed]]
[[File:Capillary system CERT.jpg|thumb|Diagram of capillary network joining the arterial system with the venous system]]

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]].<ref name="Guyton"/>

===Blood vessels===
The [[blood vessel]]s of the circulatory system are the [[arteries]], [[veins]], and [[capillaries]]. The large arteries and veins that take blood to, and away from the heart are known as the [[great vessels]].<ref name="Gray's">{{cite book |last1=Standring |first1=Susan |title=Gray's anatomy : the anatomical basis of clinical practice |date=2016 |location=[Philadelphia] |isbn=9780702052309 |page=1024 |edition=Forty-first |publisher=Elsevier Limited }}</ref>

====Arteries====
{{main|Artery}}
{{See also|Arterial tree}}
[[File:Vein_art_near.png|thumb|Depiction of the heart, major veins and arteries constructed from body scans]]
Oxygenated blood enters the systemic circulation when leaving the left ventricle, via the [[Aortic valve|aortic semilunar valve]].<ref name="Iaizzo">{{cite book|url=https://books.google.com/books?id=4PLuCgAAQBAJ|title=Handbook of Cardiac Anatomy, Physiology, and Devices|publisher=Springer|author=Iaizzo, Paul A|year=2015|page=93|isbn=978-3-31919464-6|access-date=2022-01-28|archive-date=2017-10-11|archive-url=https://web.archive.org/web/20171011044440/https://books.google.com/books?id=4PLuCgAAQBAJ|url-status=live}}</ref> 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.<ref name="Iaizzo two">{{cite book|url=https://books.google.com/books?id=4PLuCgAAQBAJ|title=Handbook of Cardiac Anatomy, Physiology, and Devices|publisher=Springer|author=Iaizzo, Paul A|year=2015|pages=5, 77|isbn=978-3-31919464-6|access-date=2022-01-28|archive-date=2017-10-11|archive-url=https://web.archive.org/web/20171011044440/https://books.google.com/books?id=4PLuCgAAQBAJ|url-status=live}}</ref> Later, it descends down and supplies branches to abdomen, pelvis, perineum and the lower limbs.<ref name="Iaizzo three">{{cite book|url=https://books.google.com/books?id=4PLuCgAAQBAJ|title=Handbook of Cardiac Anatomy, Physiology, and Devices|publisher=Springer|author=Iaizzo, Paul A|year=2015|pages=5, 41–43|isbn=978-3-31919464-6|access-date=2022-01-28|archive-date=2017-10-11|archive-url=https://web.archive.org/web/20171011044440/https://books.google.com/books?id=4PLuCgAAQBAJ|url-status=live}}</ref>

The walls of the aorta are elastic. This elasticity helps to maintain the [[blood pressure]] throughout the body.<ref name="Vaz">{{cite book|url=https://books.google.com/books?id=J_HQDwAAQBAJ&pg=PA255|title=Guyton & Hall Textbook of Medical Physiology – E-Book: A South Asian Edition|publisher=Elsevier Health Sciences|author1=Vaz, Mario|author2=Raj, Toni|author3=Anura, Kurpad|year=2016|page=255|isbn=978-8-13-124665-8|access-date=2022-01-28|archive-date=2022-01-28|archive-url=https://web.archive.org/web/20220128215455/https://books.google.com/books?id=J_HQDwAAQBAJ&pg=PA255|url-status=live}}</ref> 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.<ref name="Vaz"/>

====Capillaries====
Arteries branch into small passages called [[arteriole]]s and then into the [[Capillary|capillaries]].<ref>{{cite web | url =https://www.nhlbi.nih.gov/health/health-topics/topics/hlw/printall-index.html | title =What Are the Lungs? | author =National Institutes of Health | publisher =nih.gov | url-status=dead | archive-url =https://web.archive.org/web/20141004200807/https://www.nhlbi.nih.gov/health/health-topics/topics/hlw/printall-index.html | archive-date =2014-10-04 | author-link =National Institutes of Health }}</ref> The capillaries merge to bring blood into the venous system.<ref>{{cite web | url =https://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20100/Bio%20100%20Lectures/Organ%20Systems/Circulatory%20System/Circulatory%20System.htm | title =The Circulatory System | author =State University of New York | publisher =suny.edu | date =February 3, 2014 | url-status=dead | archive-url =https://archive.today/20140203084650/http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20100/Bio%20100%20Lectures/Organ%20Systems/Circulatory%20System/Circulatory%20System.htm | archive-date =February 3, 2014 | author-link =State University of New York }}</ref> The total length of muscle capillaries in a 70 kg human is estimated to be between 9,000 and 19,000 km.<ref>{{Cite journal |last1=Poole |first1=David C. |last2=Kano |first2=Yutaka |last3=Koga |first3=Shunsaku |last4=Musch |first4=Timothy I. |date=March 2021 |title=August Krogh: Muscle capillary function and oxygen delivery |journal=Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology |language=en |volume=253 |issue=110852 |url=https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC7867635&blobtype=pdf |doi=10.1016/j.cbpa.2020.110852 |pmc=7867635 |pmid=33242636}}</ref>

====Veins====
{{main|Vein}}
Capillaries merge into [[venule]]s, which merge into veins.<ref name="Mcconnell">{{cite book|url=https://books.google.com/books?id=BeLcDwAAQBAJ&pg=PA432|title=Human Form, Human Function: Essentials of Anatomy & Physiology, Enhanced Edition|publisher=Jones & Bartlett Learning|author1=Mcconnell, Thomas H.|author2=Hull, Kerry L.|year=2020|page=432|isbn=978-1-28-421805-3|access-date=2022-01-28|archive-date=2022-01-28|archive-url=https://web.archive.org/web/20220128215457/https://books.google.com/books?id=BeLcDwAAQBAJ&pg=PA432|url-status=live}}</ref> 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.<ref name="Floyd">{{cite book|url=https://books.google.com/books?id=V__aAAAAMAAJ|title=Understanding Pathophysiology|publisher=Mosby|author1=Parkinson, Clayton Floyd|author2=Huether, Sue E.|author3=McCance, Kathryn L.|year=2000|page=161|isbn=978-0-32-300792-4}}</ref>

====Portal veins====
{{Main|Portal venous system}}

The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. [[Portal venous system|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]] 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====
{{Main|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 [[myocardium|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]] is prevented by the [[Thebesian valve]]. The [[smallest cardiac veins]] drain directly into the heart chambers.<ref name="Guyton"/>

====Cerebral circulation====
{{Main|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 artery|internal carotid arteries]] to supply the front of the brain. The posterior circulation arises from the [[Vertebral artery|vertebral arteries]], to supply the back of the brain and [[brainstem]]. The circulation from the front and the back join ([[anastomise]]) at the [[circle of Willis]]. The [[neurovascular unit]], composed of various cells and vasculature channels within the brain, regulates the flow of blood to activated neurons in order to satisfy their high energy demands.<ref>{{Cite journal |last=Iadecola |first=Costantino |date=2017-09-27 |title=The Neurovascular Unit Coming of Age: A Journey through Neurovascular Coupling in Health and Disease |journal=Neuron |volume=96 |issue=1 |pages=17–42 |doi=10.1016/j.neuron.2017.07.030 |issn=1097-4199 |pmc=5657612 |pmid=28957666 }}</ref>

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