Earthworms are tube-shaped, segmented worms found living in soil, where they feed on organic matter. An earthworm's digestive tract is laid out straight from the oral orifice to the anus. The parts of the digestive tract regulate or absorb the nutrients from every meal.
The buccal cavity is the earthworm's mouth. Food passes through the cavity, which is not longer than two segments. It then reaches the pharynx, which is generally four segments long. The pharynx is walled by muscles that suction the food from the buccal cavity. Here mucus is released and the food is pushed into the esophagus. The esophagus has calciferous glands that release calcium carbonate to regulate bodily calcium levels.
Passing the esophagus, the food reaches the crop. Here it is stored and later released into the gizzard. The gizzard breaks down large chunks of food by grinding it against stones previously ingested by the earthworm. This helps the intestines to absorb nutrients easily. The food passing the intestine is expelled from the anus.
An earthworm releases enzymes for different nutrients during digestion, including cellulase to digest cellulose, pepsin to digest proteins, lipase to digest fats, and amylase to digest polysaccharides. Earthworm intestines are not coiled like those of mammals, thereby providing more surface area for the earthworm's system to absorb nutrients effectively from the food ingested.