Tetrapod probably had a three-chambered heart, as do modern amphibians and reptiles, in which oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enters by separate atria, and is directed via a spiral valve to the appropriate vessel — aorta for oxygenated blood and pulmonary vein for deoxygenated blood. The spiral valve is essential to keeping the mixing of the two types of blood to a minimum, enabling the animal to have higher metabolic rates, and be more active than otherwise. The difference in density between air and water causes smells (certain chemical compounds detectable by chemoreceptors) to
Splenic vein Splenic vein The splenic vein (formerly the lienal vein) is a blood vessel that drains blood from the spleen, the stomach fundus and part of the pancreas. It is part of the hepatic portal system. The splenic vein is formed when several smaller collectors leaving the spleen join shortly thereafter. It follows a course superior to the pancreas, alongside the splenic artery. It collects branches from the stomach and pancreas, and most notably from the large intestine (also drained by the superior mesenteric vein) via the inferior mesenteric vein, which drains in the splenic vein shortly before the origin of