Frog Anatomy and Physiology

The skin is smooth and slippery due to the presence of mucus.
The skin is always maintained in a moist condition.
The dorsal side of the body is generally olive green with dark irregular spots.
The ventral side of the skin is uniformly pale yellow.
Neck and tail are absent.
Above the mouth, a pair of nostrils is present.
Eyes are bulged and covered by a nictitating membrane that protects them while in water.
On either side of the eyes, a membranous tympanum (ear) receives sound signals.
The forelimbs and hind limbs help in swimming, walking, leaping, and burrowing.
The hind limbs end in five digits and are larger and more muscular than the forelimbs, which end in four digits.
Feet have webbed digits that help in swimming.

Frogs exhibit sexual dimorphism.
Male frogs can be distinguished by:
- The presence of sound-producing vocal sacs.
- A nuptial pad on the first digit of the forelimbs.
These features are absent in female frogs.

Liver secretes bile which is stored in the gall bladder.
Pancreas, a digestive gland, produces pancreatic juice containing digestive enzymes.
Food is captured by the bilobed tongue.
Digestion of food takes place by the action of $HCl$ and gastric juices secreted from the walls of the stomach.
Partially digested food called chyme is passed from the stomach to the first part of the small intestine, the duodenum.
The duodenum receives bile from the gall bladder and pancreatic juices from the pancreas through a common bile duct.
Bile emulsifies fat.
Pancreatic juices digest carbohydrates and proteins.
Final digestion takes place in the intestine.
Digested food is absorbed by the numerous finger-like folds in the inner wall of the intestine called villi and microvilli.
The undigested solid waste moves into the rectum and passes out through the cloaca.

Frogs respire on land and in the water through two different methods.
In water, the skin acts as an aquatic respiratory organ (cutaneous respiration).
Dissolved oxygen in the water is exchanged through the skin by diffusion.
On land, the lungs are a pair of elongated, pink-colored sac-like structures present in the upper part of the trunk region (thorax).
Air enters through the nostrils into the buccal cavity and then to the lungs.