A closed loop of heart, vessels, and blood
In vertebrates the circulatory system joins heart, vessels, and blood into one circuit—the cardiovascular half named from Greek kardia and Latin vascula. Blood never leaves the vessel network; lymphatics skim excess fluid beside it. Specialists split into cardiologists, vascular surgeons, and cardiothoracic teams.
Great elastic arteries and large veins frame the heart; branching continues through arterioles into capillaries that meet venules and wider veins. Plasma, red and white cells, and platelets carry oxygen, proteins, minerals, hormones, and gases while clearing wastes. Closure of the loop is the vertebrate rule—unlike many invertebrate plans that bathe tissues more openly.
The lymphatic network complements the blood circuit: capillary filtrate that becomes interstitial fluid returns as lymph through accessory routes. Circulation of lymph is slower; the system is open rather than closed, and some writers call it a secondary circulatory path. It also partners with immune surveillance.
Two main loops share one pump. The pulmonary circuit carries oxygen-poor blood from the right heart to the lungs and back to the left heart; the systemic circuit sends oxygen-rich blood from the left heart around the body and returns it through the superior and inferior venae cavae. Side routes include the coronary supply to the heart muscle itself, cerebral flow to the brain, renal flow to the kidneys and a bronchial circuit feeding the larger airways. Each circuit gets one atrium and one ventricle, giving the human heart four chambers. Returning blood enters the right atrium, passes the tricuspid valve into the right ventricle, and is pushed through the pulmonary semilunar valve toward the lungs, where carbon dioxide leaves and oxygen enters. Freshly oxygenated blood exits the left ventricle through the aortic semilunar valve into the aorta, a massive thick-walled artery that arches to supply the upper body before passing through the diaphragm at the tenth thoracic vertebra. Cardiologists treat the heart, cardiothoracic surgeons operate on it and its surroundings, and vascular surgeons handle blood and lymph vessels.
Source: Circulatory system
