Circulation and Blood Vessels

Your heart and blood vessels make up your overall blood circulatory system. Your overall blood circulatory system is made up of four subsystems.

Arterial Circulation

Arterial circulation is that part of your overall blood circulatory system that involves arteries, like the aorta and pulmonary arteries.

Arteries are blood vessels that carry blood away from your heart. Healthy arteries are strong and elastic. They become narrow between beats of the heart, and they help keep your blood pressure consistent. This helps blood circulate efficiently through your body.

Arteries branch into smaller blood vessels called arterioles. Arteries and arterioles have strong, flexible walls that allow them to adjust the amount and rate of blood flowing to different parts of your body.

Venous Circulation

Venous circulation is the part of your overall blood circulatory system that involves veins, like the vena cavae and pulmonary veins. Veins are blood vessels that carry blood to your heart. Veins have thinner walls than arteries. Veins can increase in width as the amount of blood passing through them increases.

Capillary Circulation

Capillary circulation is the part of your circulatory system where oxygen, nutrients, and waste pass between your blood and parts of your body.

Capillaries connect the arterial and venous circulatory subsystems. Capillaries are very small blood vessels.

The importance of capillaries lies in their very thin walls. Unlike arteries and veins, capillary walls are thin enough that oxygen and nutrients in your blood can pass through the walls to the parts of your body that need them to function normally. Capillaries' thin walls also allow waste products like carbon dioxide to pass from your body's organs and tissues into the blood where it's taken away to your lungs.

Pulmonary Circulation

Pulmonary circulation is the movement of blood from the heart to the lungs and back to the heart again. Pulmonary circulation includes both arterial and venous circulation.

Blood without oxygen is pumped to the lungs from the heart (arterial circulation). Oxygen-rich blood moves from the lungs to the heart through the pulmonary veins (venous circulation).

Pulmonary circulation also includes capillary circulation. Oxygen you breathe in from the air passes through your lungs into your blood through the many capillaries in the lungs. Oxygen-rich blood moves through your pulmonary veins to the left side of your heart and out the aorta to the rest of your body. Capillaries in the lungs also remove carbon dioxide from your blood so that your lungs can breathe the carbon dioxide out into the air.