Section 2

Characteristics of Amphibians

• Adult amphibians respire through their lungs and skin. Mucous glands produce slimy mucus that helps retain moisture.

• The skeleton of an amphibian supports the body against the pull of gravity. In addition, the spine interlocks to provide rigid structure, strong limbs support the body, and the pectoral and pelvic girdle transfer body weight to the limbs.

• The amphibian pulmonary circuit carries blood between the heart and lungs. The systemic circuit carries blood to the body and returns blood to the heart.

• The heart of an amphibian consists of two atria and one ventricle. The right atrium receives blood from the body, pumps blood to the ventricle, and then pumps blood to the lungs. The left atrium receives blood from the lungs, pumps blood to the ventricle, and then to the body.

Vocabulary mucous gland (p. 804) pulmonary circulation (p. 805) systemic circulation (p. 805)

pulmonary respiration (p. 806) cutaneous respiration (p. 806)

• Amphibians pump air into their lungs by raising and lowering the floor of their mouth cavity while closing and opening their nostrils.

• In an amphibian, food passes through the mouth, esophagus, stomach, small intestine, large intestine, and cloaca. The kidneys remove wastes from the blood. Adult amphibians eliminate nitrogenous wastes as urea.

• The brain of a frog has large optic lobes that process visual information, large olfactory lobes that control the sense of smell, a cerebrum that integrates behavior and controls learning, a cerebellum that coordinates movement, and a medulla oblongata that controls the heart and respiration rate. Fish have brains of similar size, but with smaller olfactory lobes.

duodenum (p. 807) ileum (p. 807) mesentery (p. 807) vent (p. 807)

nictitating membrane (p. 809) tympanic membrane (p. 809) columella (p. 809)

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