Structure and Functions of the Cardiovascular System

Your cardiovascular system consists of your heart, blood vessels, and blood. Together, they are a liquid transport network.

This system delivers oxygen and nutrients to your body and picks up waste products to eliminate. It also distributes important proteins, hormones, and other chemicals to different parts of your body and helps control your body temperature.

Your heart serves as the pump that propels blood through your cardiovascular system. Different types of blood vessels — including arteries, veins, and capillaries — work in different ways to help your circulatory system function.

Heart

Your heart is about the size of your fist and typically weighs approximately 9 to 12 ounces (oz), according to research in Frontiers in Physiology. The walls of your heart consist almost entirely of specialized muscle cells.

Under the direction of an electrical signaling system, your cardiac muscle tissue contracts in a regular, coordinated manner with each heartbeat.

Chambers

Your heart has four internal chambers that collect blood to pump to your lungs and body. The two chambers on the right side of your heart control blood flow to your lungs, or the pulmonary circulation. The two chambers on the left side of your heart control blood flow to the rest of your body, or the systemic circulation.

The two chambers at the top of your heart are called the right atrium and left atrium. The right atrium receives blood from your body to deliver to your lungs. The left atrium receives blood from your lungs that goes to the rest of your body.

The two chambers at the bottom of your heart, the right and left ventricles, pump blood away from the heart. The right ventricle pumps blood to your lungs to pick up more oxygen. The left ventricle pumps oxygen-rich blood to the rest of your body.

Valves

Four valves control blood flow through your heart to ensure that it moves in one direction during heart contractions.

• The tricuspid valve separates the right atrium from the right ventricle.
• The pulmonic valve at the exit of your right ventricle opens to allow blood flow to your lungs.
• The mitral valve separates the left atrium from the left ventricle.
• The aortic valve at the exit of your left ventricle opens to permit blood flow from the heart to the rest of your body.

Blood Vessels

Your blood vessels are hollow tubes of various sizes that carry blood to and from your heart.

Arteries and Veins

Arteries carry blood away from the heart. Most arteries carry oxygen-rich blood, except for pulmonary arteries, which carry deoxygenated blood, according to the Cleveland Clinic. Because your arterial circulation is under high pressure, arteries have thick, elastic, muscular walls.

Blood vessels that carry blood to your heart are called veins. Most veins carry deoxygenated blood, except for pulmonary veins. Your venous circulation is a low-pressure system, so veins have thinner, less elastic walls than arteries do. Veins also may have one-way valves that help blood move toward your heart and keep it from pooling because of gravity.

Capillaries

Capillaries are minute, thin-walled vessels that connect arteries and veins. They bring nutrients and oxygen to various body systems and carry away waste such as carbon dioxide, according to the Cleveland Clinic.

Your body contains approximately 10 billion capillaries, most shorter than the tip of a pencil, which cover more than 67,000 square feet, according to the journal Life. Your capillaries complete the final pickup and delivery steps of your cardiovascular system.

Blood

Your blood is the transport fluid of your circulatory system. The circulatory system of an average adult contains about 5 liters (L), or 1.3 gallons, of blood, according to StatPearls. Your blood consists of a mixture of solids called formed elements and a liquid called plasma.

Formed Elements

The formed elements of your blood include red blood cells, white blood cells, and platelets. They account for 40 to 45 percent of your blood volume, according to the American Society of Hematology.

Red blood cells carry oxygen from your lungs to your body tissues. They also pick up carbon dioxide from your tissues, which goes out through your lungs when you exhale.

The white blood cells in your blood are part of your immune system and help you fight infections.

Platelets are tiny cellular fragments that clump together to form the matrix of blood clots to stop bleeding.

Plasma

The cellular parts of your blood are suspended in a protein-rich liquid called plasma, which accounts for 55 to 60 percent of your blood volume, according to StatPearls. This liquid contains a broad array of nutrients, electrolytes, proteins, hormones, and other chemicals.

Many blood tests measure the levels of specific chemicals or elements in the liquid part of blood, plasma, or serum. They can help your doctor assess the status of your various body systems and their functions.