Tsirkulatsiooni

Tsirkulatsioon refers to the movement of fluids through an organism or system, enabling transport of gases, nutrients, wastes, and signaling molecules. In biology, it most commonly denotes the circulatory system in animals, though many organisms have fluid transport systems with different architectures. In humans and other vertebrates, the circulatory system consists of the cardiovascular subsystem and the lymphatic subsystem.

The cardiovascular system includes the heart, a network of arteries, capillaries, and veins, through which blood is pumped in two related circuits: the pulmonary circuit and the systemic circuit. In the pulmonary circuit, the right heart sends deoxygenated blood to the lungs for gas exchange, and oxygenated blood returns to the left heart. In the systemic circuit, the left heart pumps oxygen-rich blood to the body, and the deoxygenated blood returns to the right heart. Lymphatic vessels and nodes form a secondary system that drains interstitial fluid, returns it to the bloodstream, and supports immune defense.

Functions and regulation: the system transports oxygen, nutrients, hormones, and immune cells; removes carbon dioxide and metabolic wastes; helps maintain temperature and pH. Cardiac function is governed by the cardiac cycle, autonomic nerves, and hormones. Heart rate and stroke volume determine cardiac output, while local and systemic control adjusts vessel diameter and blood flow.

Variation and pathology: some invertebrates have open circulatory systems, where the fluid bathes tissues directly; others have closed systems like vertebrates. Common medical conditions include hypertension, coronary disease, arrhythmias, and heart failure, highlighting the circulation’s central role in health.