EXTERNAL COVERING • The skin of an amphibian serves two important functions— • Respiration • Protection • The skin is moist and permeable to gases and water
EXTERNAL COVERING • Numerous mucous glands supply a lubricant that keeps the skin moist • Because of their skin, amphibians are vulnerable to dehydration
INTERNAL ANATOMY • Must rely on the support of their strong internal skeleton • Weight is transferred or distributed to strong limbs that support the body
THE CIRCULATORY SYSTEM • The circulatory system of an amphibian is divided into two separate loops 1. Pulmonary Circulation carries deoxygenated blood from the heart to the lungs, then returns the oxygenated blood to the heart
The circulatory system of an amphibian is divided into two separate loops 2. Systemic Circulation carries oxygenated blood from the heart to the muscles and organs of the body and brings deoxygenated blood back to the heart
THE CIRCULATORY SYSTEM • This pattern of circulation provides a significant advantage over the “single-loop” circulation of a fish—faster blood flow to the body. In a fish, the blood loses some of its force as it passes through the narrow capillaries of the gills, and blood flow slows as a result.
RESPIRATION • Larval amphibians exchange carbon dioxide and oxygen through their gills and skin • Most adult amphibians respire through the lungs and through the skin (cutaneous respiration)
RESPIRATION • A frog breathes by changing the volume and pressure of air in its mouth while either opening or closing its nostrils • This is called positive-pressure breathing
DIGESTIVE SYSTEM • All adult amphibians are carnivorous • The amphibian digestive system includes the pharynx, esophagus, stomach, liver, gallbladder, small intestine, large intestine, and cloaca
EXCRETORY SYSTEM • The kidneys are the primary excretory organ • Like the larvae of fishes, most amphibian larvae excrete the nitrogen-containing wastes as ammonia • Adult amphibians excrete urea
NERVOUS SYSTEM • An amphibian’s brain is about the same size as that of a similarly sized fish. • The amphibian brain consists of the cerebrum, the cerebellum, and the medulla oblongata • The spinal cord and nerves are also a part of the amphibian’s nervous system
SENSE ORGANS • The senses of smell, sight, and hearing are well developed in most amphibians • All amphibians have eyes, and visual information is often important in hunting and in avoiding predators.