The cardiovascular system is a closed-loop transport system that circulates blood throughout the body. It consists of three main components working together: the heart acts as a pump, blood vessels form the transport network, and blood serves as the transport medium carrying oxygen, nutrients, and waste products.
The heart is a four-chambered muscular pump. The right side receives deoxygenated blood from the body and pumps it to the lungs, while the left side receives oxygenated blood from the lungs and pumps it to the body. Heart valves prevent backflow, opening and closing with pressure changes. The cardiac cycle consists of systole, when the heart contracts to pump blood, and diastole, when it relaxes to fill with blood.
The blood vessel network consists of three main types. Arteries carry blood away from the heart with thick muscular walls to handle high pressure. They branch into smaller arterioles, then into microscopic capillaries where nutrient and waste exchange occurs. Blood then flows into venules, which merge into veins that return blood to the heart. Veins have thinner walls and valves to prevent backflow in the low-pressure return system.
Blood consists of four main components. Plasma, the liquid portion making up 55% of blood, transports dissolved nutrients and proteins. Red blood cells comprise 44% and contain hemoglobin for oxygen transport. White blood cells, less than 1%, provide immune defense against infections. Platelets, also less than 1%, are essential for blood clotting to prevent bleeding when injuries occur.
The cardiovascular system operates through two main circulation pathways. Pulmonary circulation carries deoxygenated blood from the right heart to the lungs for oxygenation, then returns oxygenated blood to the left heart. Systemic circulation pumps oxygenated blood from the left heart to body tissues, then returns deoxygenated blood to the right heart. These two loops work continuously together to deliver oxygen and nutrients while removing waste products throughout the body.