Digestive System

All adult amphibians are carnivorous. Because most amphibians are small, insects and other arthropods are their most commonly consumed prey. Larger amphibians sometimes eat mice, snakes, fish, other amphibians, and even sometimes birds. Many amphibian larvae, such as those of frogs, are herbivorous, feeding on algae, bacteria, or plants. The larvae of some species, such as those of salamanders, are carnivorous, and some feed on the larvae of other species.

The amphibian digestive system includes the pharynx, esophagus, stomach, liver, gallbladder, small intestine, large intestine, and cloaca. Figure 40-10 shows a ventral view of the digestive system of a frog.

The elastic esophagus and stomach allow an amphibian to swallow large amounts of food. Once food reaches the stomach, tiny glands in the stomach walls secrete gastric juices that help break down, or digest, the food. A muscle called the pyloric sphincter at the lower end of the stomach relaxes, which allows digested food to move into the small intestine. The upper portion of the small intestine is called the duodenum (DOO-oh-DEE-nuhm). The coiled middle portion of the small intestine is the ileum (IL-ee-uhm). A membrane resembling plastic wrap, called the mesentery, holds the small intestine in place. Inside the small intestine, digestion is completed and the released nutrients pass through capillary walls into the bloodstream, which carries them to all parts of the body.

The lower end of the small intestine leads into the large intestine. Here indigestible wastes are collected and pushed by muscle action into a cavity called the cloaca (kloh-AY-kuh). Waste from the kidneys and urinary bladder, as well as either eggs or sperm from the gonads, also passes into the cloaca. Waste materials exit the body through the vent.

Esophagus

Liver

Gallbladder Small intestine —

Ileum

Large intestine

Accessory Glands

Other glands and organs aid in the digestion process. The liver produces bile, which is stored in the gallbladder. Bile helps break down fat into tiny globules that can be further digested and absorbed. A gland called the pancreas, located near the stomach, secretes enzymes that enter the small intestine and help break down food into products that can be absorbed by the blood.

Cloaca

Vent figure 40-10

The frog digestive system is shown in ventral view. Notice how the short small intestine is an adaptation for a carnivorous diet.

Mouth

Esophagus

The frog digestive system is shown in ventral view. Notice how the short small intestine is an adaptation for a carnivorous diet.

Mouth

Liver

Gallbladder Small intestine —

Ileum

Large intestine

Cloaca

Stomach

Pancreas

Bile duct

Duodenum

Pyloric sphincter

Mesentery

Urinary bladder

Stomach

Pancreas

Bile duct

Duodenum

Pyloric sphincter

Mesentery

Urinary bladder

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