Functioning of the heart
It is divided into two parts, the right and the left, by a blood-tight wall. Each part works as a separate pump for the blood it receives, and has an upper chamber, called auricle which receives blood from the large veins, and a lower chamber called ventricle which pumps out blood into the arteries.
From the right ventricle the veinous blood goes to the lungs for gaining oxygen and throwing out carbon dioxide. From the left ventricle, the arterial blood goes to the aorta to supple nourishment to all parts of the body.
The ventricles are so strong that when they contract, they can squeeze out almost all the blood that is contained in them.
The steady rhythm of the heart which can be heard by placing your ear on somebody’s chest or through the doctor’s stethoscope is due mainly to opening and closing of different values inside the heart while it receives and pumps out blood.
This it does, on and average, 72 times a minute, equal to your pulse rate. There is no man-made pump that compares in efficiency with your heart.
What causes the heart to beat?
It is a kind of electrical timing apparatus called the pace-maker which normally generates about 72 times a minute, a tiny electrical impulse which sweeps over the muscle fibres, causing them to contract in an orderly fashion.
Functioning of the coronary arteries
Your heart weighs 1/200th of your weight, but it receives 1/20th of the total circulating blood for its own nourishment.
This it gets, not from the blood that passes through its chambers but from the coronary arteries, the two blood vessels that are the first to come off the aorta and lie embedded in the heart muscle itself. They are not much thicker than the ordinary drinking straws.
The right coronary nourishes the back of the heart and to an extent its sides. The left coronary artery is larger than the right and divides into two major branches, viz, anterior descending and posterior circumflex.
These branches feed mainly the front and the left side of the heart. Each coronary artery after rising from the aorta, soon divides and subdivides into smaller and smaller branches so as to reach all parts of the heart muscle.
By the injection of radio-opaque materials into the coronary arteries in post-mortem specimens, it has been shown that the cross-connections (anastomoses) between the finer branches of the two coronary arteries progressively increase with age.
The anastomoses between the branches of the coronary arteries proves useful because when one branch gets blocked, the area that it served before, now receives blood supply from the other anastomosing branches.
This phenomenon, however, depends upon several factors, the most important of which is the speed with which the blockade occurs; if it occurs suddenly and completely, then the anastomosing channels cannot, at once, come to the rescue.
Flaming and Schwarz of the University of Heidelburg in West Germany, showed in their experimental studies that coronary anastomoses also termed as collaterals, are able to maintain resting coronary flow after complete coronary obstruction.
The functional significance of these well-developed collaterals, however, is limited, and blood flow becomes inadequate under stress conditions. In man, they found, that coronary collaterals compensated for the coronary obstruction only partially.