Kenneth Harper, age 12, of Marion, Ohio, for his question:
HOW LARGE IS THE HUMAN HEART?
Your heart pumps blood, which carries oxygen and nourishment to tissues in all parts of you: body and carries out wastes. Your heart is about the size of your fist. As the size of your fist grows, so does the size of your heart.
The heart of an adult is about five inches long, about three inches wide and about 2 1/2 inches thick. A man's heart will weigh about 11 ounces while a woman's will weigh about nine ounces.
The widest part of the heart is at the top, called the base, and the narrowest is at the bottom, or apex. There are four compartments, or chambers, in the heart. The two upper chambers are called the atria, while the two lower ones are called the ventricles. The atria are separated from each other by a membrane called the interventricular septum.
Valves are located between the right atrium and right ventricle and the left atrium and left ventricle. They allow the blood to flow from the atria to the ventricles but not back again.
There are two other valves: one between the right ventricle and the pulmonary artery and one between the left ventricle and the aorta.
All valves open and shut with each beat of the heart.
Actually, the heart is made up of two pumps working together. The pump on the right side receives blood low in oxygen but high in carbon dioxide and sends it to the lungs, where carbon dioxide is taken out and oxygen added. The left pump receives blood from the lungs and sends it throughout the body.
The atria have thin muscular walls because they send blood only to the lower chambers. The right ventricle has thicker walls because it pumps blood through the pulmonary circuit to the lungs. The thickest walls of all are found in the left ventricle, which must pump blood the farthest.
A child's heart beats from 90 to 100 times per minute, while the heart of an adult will beat between 70 and 80 times each minute.
Without a doubt, the heart is the single most important organ in your entire body. Life absolutely depends on it.
The heart, which is located nearly in the center of the chest but a little to the left, works about one third of the time. Between beats it rests. During each rest period the pressure in the blood vessel is maintained by the elastic action of the arteries against the volume of blood they hold.
Your heart is connected to a system of about 100,000 miles of veins, arteries and capillaries that ensure a continuous flow of oxygen and nutrients to your brain, vital organs and body tissue.
Your heart beats more than 100,000 times in a single day. Every 60 seconds it pumps about five quarts of blood through its chambers.
In one hour your heart does enough work to lift a weight of 1 1/2 tons more than one foot off the ground.