Editing Snake (section)

=== Internal organs ===
{{snake anatomy imagemap}}
Snakes and other non-[[archosaur]] ([[crocodilia]]ns, [[dinosaur]]s + [[bird]]s and allies) reptiles have a three-chambered heart that controls the [[circulatory system]] via the left and right atrium, and one ventricle.<ref>{{cite journal |vauthors=Jensen B, Moorman AF, Wang T |title=Structure and function of the hearts of lizards and snakes |journal=Biological Reviews of the Cambridge Philosophical Society |volume=89 |issue=2 |pages=302–36 |date=May 2014 |pmid=23998743 |doi=10.1111/brv.12056 |s2cid=20035062}}</ref> Internally, the ventricle is divided into three interconnected cavities: the cavum arteriosum, the cavum pulmonale, and the cavum venosum.<ref>{{cite journal |last1=Burggren |first1=Warren W. |name-list-style=vanc |title=Form and Function in Reptilian Circulations |journal=Integrative and Comparative Biology |date=1 February 1987 |volume=27 |issue=1 |pages=5–19 |doi=10.1093/icb/27.1.5 |language=en |issn=1540-7063 |doi-access=free}}</ref> The cavum venosum receives deoxygenated [[blood]] from the right atrium and the cavum arteriosum receives oxygenated blood from the left atrium. Located beneath the cavum venosum is the cavum pulmonale, which pumps blood to the pulmonary trunk.<ref>{{cite journal |last1=Mathur |first1=Prahlad |name-list-style=vanc |title=The anatomy of the reptilian heart. Part I. Varanus monitor (Linn.) |journal=Proc. Ind. Acad. Sci. |date=1944 |volume=Sect. B 20 |pages=1–29 |url=https://www.ias.ac.in/article/fulltext/secb/020/01/0001-0029 |access-date=May 10, 2019 |archive-date=10 May 2019 |archive-url=https://web.archive.org/web/20190510203803/https://www.ias.ac.in/article/fulltext/secb/020/01/0001-0029 |url-status=live }}</ref>

The snake's heart is encased in a sac, called the ''[[pericardium]]'', located at the [[:wiktionary:bifurcation|bifurcation]] of the [[bronchi]]. The heart is able to move around, owing to the lack of a diaphragm; this adjustment protects the heart from potential damage when large ingested prey is passed through the [[esophagus]]. The [[spleen]] is attached to the [[gall bladder]] and [[pancreas]] and filters the blood. The [[thymus]], located in fatty tissue above the heart, is responsible for the generation of immune cells in the blood. The cardiovascular system of snakes is unique for the presence of a renal portal system in which the blood from the snake's tail passes through the kidneys before returning to the heart.<ref name="Mader"/>

The circulatory system of a snake is basically like those of any other vertebrae. However, snakes do not regulate internally the temperature of their blood. Called [[Ectotherm|cold-blooded]], snakes actually have blood that is responsive to the varying temperature of the immediate environment. Snakes can regulate blood temperature by moving. Too long in direct sunlight, the snakes' blood is heated by beyond tolerance. Left in the ice or snow, the snake may freeze. In temperate zones with pronounced seasonal changes, snakes denning together have adapted to the onslaught of winter.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}

The [[vestige|vestigial]] left [[lung]] is often small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin.<ref name="Mader">{{Cite journal |last=Mader |first=Douglas |name-list-style=vanc |title=Reptilian Anatomy |journal=Reptiles |volume=3 |issue=2 |pages=84–93 |date=June 1995}}</ref> In the majority of species, only one lung is functional. This lung contains a vascularized anterior portion and a posterior portion that does not function in gas exchange.<ref name="Mader"/> This 'saccular lung' is used for [[hydrostatic]] purposes to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species.<ref name="Mader"/> Many organs that are paired, such as [[kidneys]] or [[reproductive organs]], are staggered within the body, one located ahead of the other.<ref name="Mader"/>

The snake with its particular arrangement of organs may achieve a greater efficiency.{{compared to?|date=April 2024}} For example, the lung encloses at the part nearest the head and throat an oxygen intake organ, while the other half is used for air reserve. The esophagus-stomach-intestine arrangement is a straight line. It ends where intestinal, urinary, and reproductive tracts open, in a chamber called the cloaca.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}

Snakes have no [[lymph node]]s.<ref name="Mader"/>