Respiratory Organs In Amphibians
Check us out at http://www.tutorvista.com//videos The frog is covered by a soft, thin, moist skin composed of two layers, an outer epidermis and an inner dermis (see Skin). The skin does not merely protect the frog but helps in respiration (see Respiratory System). An extensive network of blood vessels runs throughout the frog's skin. Oxygen can pass through the membranous skin, thereby entering directly into the blood. When a frog submerges beneath the water, all its respiration takes place through the skin. Oxygen is obtained directly from the water. The frog does not breathe through its skin alone. Adult frogs have paired, simple, saclike lungs. As in man, air enters the body through two nostrils, passes through the windpipe, and is received by the lungs (see Lungs). The mechanism of breathing, however, is different in the frog from that in man. In humans breathing is aided by the ribs, the diaphragm, and the chest muscles. The frog has no ribs or diaphragm, and its chest muscles are not involved in breathing. A frog may breathe by simply opening its mouth and letting air flow into the windpipe. However, it may also breathe with its mouth closed. The floor of the mouth is lowered, causing the frog's throat to "puff out." When the nostrils open, air enters the enlarged mouth. Then, with nostrils closed, the air in the mouth is forced into the lungs by contraction of the floor of the mouth.