Dog Heart

The body is nourished by the blood, which delivers to the cells the substances they need and picks up their wastes and delivers them to the organs of excretion. At the center of this circulatory system is the heart, a natural pump which for efficiency is not excelled by any man-made device.

The heart receives blood via two veins, the anterior and posterior vena cava, then squeezes or contracts so that the blood is driven first into the lungs, where it liberates a gas, carbon dioxide, takes up another gas, oxygen, and is then hustled back to the heart to be pumped around the body via the arteries to distribute the oxygen and pick up cell wastes.

The great arteries, which carry the blood from the heart, start dividing into smaller arteries, which in turn divide into smaller and smaller ones, called arterioles, and thence into capillaries. From the capillaries the blood returns to the heart via venues, veins, and finally large veins. It also returns in lymph vessels. (The lymph may be thought of as concentrated blood without red blood cells.)

The pump keeps up its contracting squeezes and relaxations rhythmically for the life of the dog. It sounds like a continuous Tubby dub, Tubby, dub in the chest and, in an eight-pound dog, pumps about quart of blood every minute. Everything about it is a marvel - the delicate valves, its strength, its four chambers, the skin around it, called the pericardium, the nervous mechanism that causes it to beat.

Spleen and Lymph Nodes

All along the path of the blood and lymph are filter organs, the chief of which is the spleen. A dog's spleen weighs about one ounce for every twenty-five pounds of body weight. It is a flat, long, narrow organ which lies close to the stomach. The spleen's function is chiefly to help purify the blood. It destroys great numbers of bacteria, and when red blood cells become aged the spleen breaks many of them down into liquid. In addition, the spleen manufactures a certain number of red and white blood cells. Since the blood spaces in the spleen are very large compared with ordinary capillaries, when the organ is ruptured in an accident a major hemorrhage into the abdomen may occur and this can be fatal.

The spleen, a part of the lymphatic system, is the principal filter organ of the blood. Other smaller glands situated along the lymph vessels also serve to remove solid impurities, such as bacteria, from the blood fluids. Lymph does not move about by blood pressure, but rather by the body's movements. Muscle movement, the expansion and con-traction involved in breathing, intestinal movements, and others, all force the lymph through the nodes and along its course. Valves in both lymph vessels and veins permit flow in only one direction.

The heart diseases in dogs are one of the main causes of deaths in dogs after the incidence of cancer. Almost 15 % of the dogs die out of chronic heart diseases.