CIRCULATORY SYSTEMS OF THE REPRESENTATIVE CHORDATES

The circulatory system functions, primarily, as the major transport system of the vertebrate body. Oxygen and food are carried from sites of absorption to all tissues and carbon dioxide and other wastes are carried from the tissues to sites of removal. Hormones are also transported by the circulatory system.

The closed circulatory system of vertebrates consists of the heart, arteries, veins, capillaries and blood. Arteries carry blood away from the heart to the sites of exchange in the tissues, in the capillaries. Veins carry blood from tissue capillaries back to the heart.

The circulatory system of the perch is a typical low pressure single type system in which the heart is a single pump and there is a single circuit of blood flow. Venous blood from the body is pumped through the heart forward to the gills. From the gills, where it is oxygenated, the blood goes directly to the body. Thus the blood makes a single circuit during which it is pumped, oxygenated and distributed to the body, before it returns to the heart. In this pattern of circulation the heart pumps only deoxygenated blood.

The circulatory system of the rat typifies the high-pressure double circulatory system of mammals in which the heart is a double pump and there are two circuits of blood flow, systemic and pulmonary. In this type of system, blood is pumped through the heart twice. Deoxygenated blood from the body is pumped to the lungs where it is oxygenated (pulmonary circulation). Oxygenated blood from the lungs returns to the heart whereupon it is pumped to the rest of the body (systemic circulation). Thus the heart pumps both oxygenated and deoxygenated blood.