Frog Digestive System

Like other vertebrates, the frog's digestive system is a continuous alimentary canal running from the mouth to a terminal opening, together with a set of associated glands that secrete digestive juices into that canal. Food enters through the wide buccal (mouth) cavity, where the frog's most distinctive feeding structure, a bilobed, sticky, protrusible tongue, is attached at the front of the lower jaw rather than at the back as in most other vertebrates; this reversed attachment lets the frog flick its tongue rapidly outward to catch insects and other small prey before drawing it back into the mouth. Small, backward-curving teeth are present along the margin of the upper jaw (maxillary teeth) and on the roof of the mouth (vomerine teeth), but these teeth are used only to grip and hold struggling prey in place — they play no part in chewing, since the frog swallows its food whole.

From the buccal cavity, food passes through a short, wide, muscular oesophagus into the stomach, a curved, J-shaped, muscular sac lying on the left side of the body cavity. In the stomach, the food is churned by muscular contractions of the stomach wall and mixed with gastric juice, beginning its chemical breakdown, particularly of proteins. The partially digested food, now called chyme, then passes into the small intestine, which is differentiated into an initial short duodenum (into which the ducts from the liver and pancreas open) followed by a long, coiled ileum; it is here, in the small intestine, that digestion of proteins, carbohydrates and fats is completed by the combined action of bile, pancreatic juice and the intestine's own secretions, and that the resulting simple, absorbable nutrient molecules are taken up across the intestinal wall into the blood. The small intestine leads into a short, wide large intestine or rectum, which absorbs water from the undigested residue and stores the resulting solid waste before it is voided. Rather than opening independently to the exterior, the rectum opens into a common chamber, the cloaca, which also receives the ducts of the urinary and reproductive systems and opens to the outside through a single cloacal aperture — a shared arrangement typical of amphibians, reptiles and birds, in contrast to the separate digestive, urinary and reproductive openings of most mammals. …