Circulatory System

The circulatory system is the body system that transports blood, carrying oxygen, nutrients, hormones, and waste products. It consists of the heart, which pumps blood, and blood vessels (arteries, veins, and capillaries), along with blood itself.

This system operates in a continuous loop: blood leaves the heart, circulates through the body, and returns to the heart. It also connects with the lymphatic system, which collects fluid from body tissues and returns it to the circulatory system.

The Heart

The heart is a specialized muscle with four chambers: two atria (upper chambers) and two ventricles (lower chambers). The right upper chamber receives deoxygenated blood returning from the body and sends it to the right ventricle, which pumps it to the lungs. The left side receives oxygen-rich blood from the lungs and pumps it throughout the body. Valves within the heart prevent blood from flowing backward.

The Two Circulations

The pulmonary circulation carries blood to the lungs, where oxygen is taken up and carbon dioxide is removed. The systemic circulation distributes oxygen-rich blood to all body tissues and returns deoxygenated blood to the heart.

Blood Vessels

Arteries carry blood away from the heart and have thick, elastic muscular walls. Veins return blood to the heart and often contain small valves that prevent backflow. Capillaries are extremely thin-walled vessels where oxygen, nutrients, and waste products are exchanged between blood and body tissues.

Blood and Other Functions

Blood consists of plasma (fluid) and cells: red blood cells that carry oxygen, white blood cells that defend the body, and platelets that aid in clotting. The circulatory system also regulates body temperature, distributes hormones, and maintains fluid and electrolyte balance.