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The Heart


Dr. Mansfield
The heart's job is to circulate blood throughout the body in order to supply oxygen and nutrients to all the body's organs and tissues. Dr. Patel, what can you tell us about the heart?

Dr. Patel
Well, Dr. Mansfield, a healthy heart is a muscle about the size of an average adult fist. Every time the heart beats, it contracts, sending blood into the arteries. Blood returns to the heart through the veins.

The heart has four chambers: the right and left atria, and the right and left ventricles. The atria are the upper chambers, and they receive blood that is being returned to the heart.

The right atrium receives blood low in oxygen because it receives blood that has just circulated throughout the body releasing oxygen and delivering nutrients to tissues. The left atrium fills with newly oxygenated blood returning from the lungs.

When the atria pump, they push the blood through one-way flaps called valves into the right and left ventricles. When the ventricles contract, the right ventricle pumps blood to the lungs, and the left ventricle pumps blood through the aorta to the rest of the body. The left ventricle also supplies blood to the heart muscle itself through the coronary arteries.

The heart is controlled by its own electrical system. Each beat of the heart starts with an electrical signal from the sinoatrial, or SA, node in the right atrium. The signal causes the atria to contract and push blood into the ventricles. This electrical signal then travels through a series of nodes and fibers into the cells of the ventricle walls, causing the ventricles to contract and send blood to the lungs and the rest of the body.

A person's pulse is the number of signals produced by the SA node per minute. While a person is resting, their pulse is approximately 60 to 100 beats per minute. During exercise, however, their muscles require more oxygen and nutrients to work harder, so the heart beats faster, and their pulse goes up.