Circulatory

The circulatory system is the organ system that transports blood and other substances throughout the body. It consists of the heart, blood vessels, and blood, and in mammals interacts with the lymphatic system. Its primary purpose is to supply tissues with oxygen and nutrients, remove wastes, and help regulate temperature and pH.

The heart acts as a muscular pump with four chambers: right atrium, right ventricle, left atrium, and left ventricle. Blood flows through a sequence of valves that ensure one-way movement. In the systemic circuit, the left ventricle pumps oxygenated blood to the body; in the pulmonary circuit, the right ventricle sends deoxygenated blood to the lungs. The coronary vessels supply the heart muscle itself.

Blood vessels form a closed network of arteries, veins, and capillaries. Arteries carry blood away from the heart, veins carry it toward the heart, and capillaries enable the exchange of gases, nutrients, and wastes with tissues. Blood consists of plasma and formed elements: red cells for oxygen transport, white cells for immunity, and platelets for clotting.

Functions include transport of oxygen, carbon dioxide, nutrients, hormones, and wastes; immune defense; hemostasis; and temperature regulation.

Regulation is achieved through autonomic nervous system control of heart rate and vessel tone, hormonal influences, and local metabolic factors. Development begins early in embryogenesis with formation of the heart tube and vascular system; the heart forms chambers and valves as it matures.

Common pathological conditions affecting circulation include hypertension, atherosclerosis, heart failure, and venous insufficiency. Diagnostic tools include electrocardiography (ECG), echocardiography, Doppler ultrasound, and blood tests.