Your Heart & Circulatory System

Posted: Feb. 1, 2005

The circulatory system keeps blood moving throughout the body. It is made up of the heart, blood vessels and blood.

Your blood carries oxygen and nutrients to cells throughout the body. There are two paths for the blood cells. One path has blood flow moving from the heart to the lungs and back to the heart again. The other path moves blood from the heart to the rest of the body and back to the heart again.

How the heart works
The heart is a muscle about the size of your fist. It works like a pump and beats 100,000 times a day.

The heart has two sides, separated by an inner wall called the septum. The right side of the heart pumps blood to the lungs to pick up oxygen. Then, oxygen-rich blood returns from the lungs to the left side of the heart, and the left side pumps it to the body.

Heart chambers
The heart has four chambers or "rooms,"— two on the left side of the heart and two on the right.

The atria are the two upper chambers that collect blood as it comes into the heart.

The ventricles are the two lower chambers that pump blood out of the heart to the lungs or other parts of the body.

Heart valves
Four valves control the flow of blood from the atria to the ventricles and from the ventricles into the two large arteries connected to the heart.

Valves are like doors that open and close. They open to allow blood to flow through to the next chamber or to one of the arteries, and then they shut to keep blood from flowing backwards.

When your heart's valves open and close, they make the familiar "lub-DUB" or "lub-DUPP" sounds that your doctor can hear using a stethoscope.

The four valves are:

• The tricuspid valve in the right side of the heart, between the right atrium and the right ventricle.
• The pulmonary valve in the right side of the heart, between the right ventricle and the entrance to the pulmonary artery, that carries blood to the lungs.
• The mitral valve in the left side of the heart, between the left atrium and the left ventricle.
• The aortic valve in the left side of the heart, between the left ventricle and the entrance to the aorta, the artery that carries blood to the body.

Arteries
The arteries are major blood vessels connected to your heart.

• The pulmonary artery carries blood pumped from the right side of the heart to the lungs to pick up a fresh supply of oxygen.
• The aorta is the main artery that carries oxygen-rich blood pumped from the left side of the heart out to the body.
• The coronary arteries are the other important arteries attached to the heart. They carry oxygen-rich blood from the aorta to the heart muscle, which must have its own blood supply to function.

Veins & capillaries
The veins are also major blood vessels connected to your heart.

• The pulmonary veins carry oxygen-rich blood from the lungs to the left side of the heart so it can be pumped out to the body.
• The vena cava is a large vein that carries oxygen-poor blood from the body back to the heart.
• Capillaries are very thin blood vessels that connect the arteries and veins.

Source: National Heart, Blood and Lung Institute

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