Digestive System of Frog | With Functions and Labelled Diagram

The digestive system of the frog includes the alimentary canal (alimentary tract) and the various associated digestive glands.

Digestive System of Frog

The alimentary canal of the frog is complete.

It is a long, coiled tube of varying diameter that extends from the mouth to the cloacal aperture of the frog.

The Alimentary canal comprises

• Mouth
• Buccal cavity
• The pharynx or windpipe
• Oesophagus
• Stomach
• Small intestine
• Large intestine
• Cloaca aperture

Mouth

• The alimentary canal of the frog starts from the mouth. It is part of the head.

• It is a wide opening, extending from one side of the snout to the other.

• The mouth of the frog is bounded with two bony jaws that are covered with immovable lips.

• The upper jaw is fixed and immovable like in higher animals.

• But, the lower jaw is movable and moves up and down to close and open the mouth.

Buccal cavity

• The mouth of the frog opens into a large, shallow oral cavity, which is called a buccal cavity.

• The buccal cavity is lined with ciliated columnar epithelial cells that contain mucus. This mucus is helpful in lubricating the food and inside the buccal cavity.

• Frog has no salivary glands.

• The lower jaw lacks teeth, but some conical and backwardly pointed teeth occur in a row on either side on the premaxillae and maxillae bones in the upper jaw.

• Two small bones are found in the roof of the mouth, called vomers, which also bears two groups of vomerine teeth.

• The teeth in the frog are not meant for chewing; they are simply required for the catching of their prey, holding it firmly, and preventing its prey from slipping from its capture.

• The teeth of a frog are homodont (same type), acrodont (do not have a tooth socket). But, the tooth is attached to the jaw bone.

• In the life cycle of the frog, teeth are replaced several times (polyphyodont) throughout their life by the growth of new teeth when old ones are worn out or lost.

• On the floor of the buccal cavity lies a large, protrusible muscular sticky tongue.

• The tongue’s anterior end is attached to the inner border of the lower jaw, and the posterior end is free and bifid

• This tongue can be flicked out and retracted suddenly after the capture of the prey.

• The surface of the tongue is slimy in nature to stick to its prey.

Pharynx

• Posteriorly, the buccal cavity of frog passes without demarcation into a short pharynx.

• Hence, the two sometimes are defined together as the Bucco-pharyngeal cavity.

• Several apertures open in the pharynx. In male frogs, small openings of the vocal sacs are located on either side at the floor near the angle of the jaws.

• These vocal sacs act as resonators during croaking to help the frog call for a mate.

• Pharynx tapers abruptly at the back, leading into the esophagus through a wide opening, called the gullet.

Esophagus

• The esophagus is the food pipe that traverses from pharynx to the stomach of the alimentary canal.
• It is a short, wide, muscular and highly distensible tube that has a mucous epithelial lining that contains some mucous glands.
• The longitudinal foldings of the esophagus allow its expansion during the passage of food into the stomach.  The esophagus’s glandular lining secretes an alkaline digestive fluid. In the peritoneal cavity, the food pipe or esophagus enlarges to merge with the stomach.

Stomach

• The stomach of a frog lies in the left side of the body cavity.

• It is attached to the body wall by a mesentery called mesogaster.

• Mesogaster is the large (4cm), broad, and slightly curved bag or tube with thick muscular walls.

• The large broader anterior part is called a cardiac stomach, while the short narrower posterior part is called the pyloric stomach.

• The inner surface of the stomach contains many prominent longitudinal folds which allow its distension when food is consumed.

• The stomach’s mucous epithelium secretes an enzyme called pepsinogen, and unicellular oxyntic glands secrete hydrochloric acid.

• The posterior or the pyloric stomach is minutely constricted, and the opening is guarded by a circular ring-like sphincter muscle, called the pyloric valve.

Small Intestine

• The small intestine of a frog is a long, coiled, narrow tube of about 30cm long, and it attaches mid-dorsally to the body wall by mesenteries.

• The small intestine is composed of two parts: a small anterior duodenum and longer posterior ileum.

• The mucosal lining of the intestine consists of two types of cells besides the intestinal glands, like

1. large goblet cells, and
2. small absorbing cells.

• The goblet cells contain oval vacuoles and granular substances, that secrete mucus.

• The absorbing cells have oval nuclei near the base.

Duodenum

• The duodenum runs parallel to the stomach, forming a U-shaped structure.

• It receives hepatopancreatic duct from the liver and pancreas, which brings bile and pancreatic juice.

• The internal mucous forms the low transverse folds.

Ileum

• The ileum is the longest part of the digestive system of the frog, which makes several loops before dilating into the large intestine.

• The internal mucous lining of the ileum forms many longitudinal folds, but there are no true villi seen in frogs.

• Digestion of food and the absorption of the same is done here in the small intestine.

Large intestine or Rectum

• The large intestine or rectum is a short, wide tube, about 4 cm long.

• It runs straight behind to open into the cloaca by the anus.

• The anus is guarded by anal sphincter.

• The inner lining has many longitudinal folds.

• The main function is re-absorption of water and preparation and storage of feces.

Cloaca

• The cloaca is the small terminal sac-like part which opens to the exterior via the anus and the urinogenital apertures.

• Cloaca lies in the hind end of the body.

Associated digestive glands

Besides the gastric glands and intestinal glands, two large glands, namely the liver and pancreas, also play a vital role in the digestion of food.

Liver and its function

• The liver is the largest organ in the body cavity of a frog.

• It is reddish-brown in color, the multilobed gland, which is situated close to the heart and lungs.

• The liver of frogs consists of 3 lobes –right, left, and median.

• The polygonal cells of the liver secrete a greenish alkaline fluid called bile.

• Bile gets stored in a large sac-like structure called the gall bladder, which lies between the lobes of the liver.

• Bile has no digestive purpose except to emulsify fats for proper digestion.

Pancreas and its function

• The pancreas of frogs is much-branched than that of any vertebrate.

• The pancreas is branched, an irregular, flattened, and yellow-colored gland that lies in the mesentery between the stomach and the duodenum.

• The pancreas has a dual nature, i.e., both exocrine, as well as endocrine.

• The endocrine part consists of the islets of Langerhans, which manufacture the insulin hormone.

• The exocrine part secretes pancreatic juice, which contains many digestive enzymes for the digestion of food.

• The pancreas doesn’t have any separate duct; the juice is conveyed through the hepatopancreatic duct.

Frog Digestive System: Organs & Their Functions

Frog Digestive System FAQs

References:

• Cloaca
• Examples of Tooth Attachments