An earthworm Digestive System is quite similar to higher animals. It ingests food by the pumping action of its pharynx. The food is engulfed by the earthworm by rhythmic contractions of the pharyngeal wall, which further leads to the buccal chamber. The mouth has only one work which is to feed on its prey.
The Earthworm digestive system
The earthworm digestive system comprises of following parts:
The alimentary canal in earthworm is seen complete, which runs along the entire length of the body from the anterior mouth to the posterior anus. The alimentary canal is subdivided into various parts which are:
- Buccal chamber
The crescentic mouth is present at the anterior end of the peristomium towards the ventral side of the prostomium which further leads to a protrusible, short, narrow buccal chamber, extending up to the middle of the third segment of the earthworm body. The longitudinal folds are seen in the inner epithelium.
The pharynx in earthworm is pear-shaped and muscular which extends up to the fourth segment of the body. The buccal chamber dilates into the pharynx. The anterior end has the appearance of a nerve ring placed in a transverse groove between the pharynx and the buccal chamber. The cavity of the pharynx is somewhat flattened due to the presence of a large glandular pharyngeal mass on the roof of the pharynx which secretes the salivary secretions for the mixing with food. The horizontal shelf is formed on the lateral walls of the pharynx. It makes distinct the pharyngeal cavity into the dorsal or salivary chamber and a ventral or conducting chamber. Salivary secretions comprise of mucus and proteolytic enzymes which helps in the digestion process which is poured in the salivary chamber.
The esophagus lies behind the pharynx which is also called the gullet. it is a short, narrow, thin-walled tube that extends up to the seventh segment.
The gizzard is an oval, hard and prominent structure that lies in the eighth segment of the body of earthworm.gizzard is the modification of the esophagus. It is a thick-walled muscular organ consisting of muscle fibers that are lined by a tough cuticle.
Gizzard ends up in the narrow tube called stomach which extends from the 9th segment to the 14th segment of the earthworm. The presence of sphincter is seen at every end of the segments lying stomach. The walls of the stomach are highly vascular and glandular and the wall is thrown into transverse folds.
The part next to the stomach is called intestine which is a long, wide, and thin-walled tube extending from the 15th segment to the last segment. the intestine has a beaded appearance because of the constrictions present at the septa. The internal lining is ciliated, folded, vascular, and glandular.
The intestine is divisible into following :
- Pre-typhlosole region:
The pre-typhlosole region lies between the 15-26th segment in an anterior position in the earthworm. The walls of this region have numerous folds or minute process called villi and have a rich supply of blood vessels. From the 26th segment, a pair of forwardly-directed lateral conical outgrowth is seen. Intestinal caeca run-up to 22nd and 23rd segments. This intestinal caecum has the lining of vascular vessels. Villi-like processes are seen.
- Typhlosolar region
The second part or middle part of the intestine lies between 27th segments up to the 23-25 segments in front of the anus. This part is characterized by glandular, vascular longitudinal ridges, arising as a median to the growth of the dorsal side of the intestinal orifice. This is called as typhlosole.
- Post-typhlosole region
The last part of the intestine is called rectum, which is about 23-25 segments. the longitudinal folds are present. It opens to outside through a terminal anus.
Physiology of digestion in Earthworm Digestive System
Ingested food moves posteriorly in the earthworm. No type of digestion takes place inside the buccal chamber. As the food passes through the pharynx, it meets with the salivary secretions of the pharyngeal mass and pours into the pharyngeal chamber for the mixing up. The secretion contains mucin, which lubricates the food, and an enzyme act on the food called protease which digests protein. Food now makes its way to the gizzard through the stomach. Gizzard acts as a grinding machine which has work of grinding and further pulverizes the food masses.in the stomach, a chalky substance is secreted from the calciferous glands of the stomach wall, neutralizes the humic acid present in the soil which gets devoured along with food. Intsetine is the main organ for the digestion of food, where the intestinal walls secrete digestive juices containing pepsin, trypsin, amylase, lipase, and cellulase.
The digestion is extracellular in the earthworm. The intestines absorb most of the digested food required by the earthworm and pass out the indigested food outside of the body through the anus. The presence of typhlosole in the greater a part of the intestine increases the surface both for digestion and absorption.