DIGESTION IN EARTHWORM

Earthworm possesses a tubular digestive system which is highly specialized. At one end of this system is present mouth while at the other, anus. Digestive system of earthworm consists of following parts.

 

MOUTH

        Mouth is present at the anterior end and opens behind into a short, wide, thin walled buccal cavity. A small lobe overhang the mouth.

 

PHARYNX

        Buccal cavity leads into the pharynx which has thick, muscular walls. The pharynx can slightly protrude out of the mouth to suck soil containing decaying organic matter which is the food of the earthworm. The pharynx has pharyngeal glands in the the form of mucous goblet cells and glandular mass. These glands secrete mucous ( a secretion that moistens and protects cells) and a proteolytic enzyme ( protein breaking ) into the pharyngeal cavity.

 

OESOPHAGUS

       The pharynx is followed by oesophagus which is a thin walled narrow tube having internal glands. These glands secrete crystals of calcium carbonate that help to neutralize organic acids in foods. Thus food is easily acted on by the alkaline digestive juice of the intestline.

 

GIZZARD

      The oesophagus leads into a thick-walled, muscular region called the gizzard. The lining of the heavy muscular walls has a distinct cuticle. Food materials are ground and broken into extremely small particles. Some part behind the gizzard is also narrow and may be called oesophagus but it is known as stomach due to the presence of important glands.

 

INTESTINE

      The oesophagus or stomach opens into intestine. The cells of lining of the intestine secrete enzymes that complete the process of digestion. This part of the intestine has its dorsal wall folded into a U-shaped structure known as typhlosole which increase the area for absorption. There is also a pair of very small intestinal caeca in the anterior region. These caeca pour digestive juices.

        The food is absorbed by the intestinal epithelium and directly passed into the blood through the capillaries of the intestine by means of diffusion and active transport.

 

RECTUM

    The last part of the intestine may be called rectum. The undigested food material may be stored in it and then passed out through anus, usually in the form of pellet-like castings.