DIGESTIVE SYSTEM OF PHERETIMA - IMP QUESTION FOR IPE

1. Describe the digestive system in Pheretima with the help of  a diagram?
(March 2005, May 2007, March 2010 , MARCH 2011)
Ans : The digestive system consists of the alimentary canal and the associated digestive
       glands. The  alimentary canal consists of  the following parts.
1) MOUTH* It is a crescentic aperture  present at the anterior end,  ventrally on the first segment  called Peristomium
* The extension of the first segment over hangs like a lip infront of the mouth, called prostomium.
2) BUCCAL CHAMBER
* The  mouth leads into Buccal chamber.
* The Buccal chamber extends from the first to the middle of the third segments
* The walls of the Buccal chamber turn inside out and the Pharynx ( everts ) comes out through the mouth
   and helps in digging the soil.
3) PHARYNX* Buccal chamber leads into Pharynx.
* It occurs in the third and fourth segments.
* Its wall is muscular and contains several blood cells.
* Its Dorsal side is folded and consists of a glandular structure called Pharyngeal bulb, thelateral wall is
  pushed inwards to form a pair of lateral folds called shelves.
* They divide the pharyngeal cavity into 2 compartments, called the dorsal salivary chamber and the ventral
   conducting chamber.
* The chromophilic cells of Pharyngeal bulb secrete proteolytic enzymes and mucus that help in protein   digestion.
* The ventral conducting chamber helps in passing the food.
4) OESOPHAGUS* The Pharynx opens into the oesophagus.
* The oesophagus is a narrow tube extending from the 5th
   to 8th segments.
5) GIZZARD* Oesophagus in 8th segment opens into the gizzzard .
* It is an oval shaped hard muscular chamber .
* It has thick wall of circular muscles and inner lining of chitinous cuticle.
* It grinds the food material into fine particles.
* It is commonly called “ grinding mill “.3
6) STOMACH* The gizzard leads into the stomach.
* The stomach extends from the 9th to the 14th segment.
* It is a highly vascular and glandular tube.
* Its inner foldings contain gland cells, which secrete proteolytic enzymes, that  help in protein dig estion.
7) INTESTINE :* Stomach opens into the long and wide intestine which extends from the 15th
 to the last segment.
* It’s mid dorsal fold is called typhlosole. This is poorly developed in Pheretima.
* It increases the area of absorption of food.
* On the basis of the presence of typhlosole the intestine is divisible into 3 regions.
1) Pre-typhlosolar region 2) Typhlosolar region 3) Post-typhlosolar region
1) Pre-typhlosolar region :* This is the proximal part of the intestine located from 15th to 25th segments.
* In the 26th segment, a pair of conical outgrowths, the intestinal caecae arise form this region laterally
   and extend forward over three or four segments.
* They secrete digestive juices, which contain amylase enzyme.
* Typhlosole  is absent in this part of intestine.
2) Typhlosolar region :* It starts from 26th segment and terminates  in 23 or 25 segments ahead of the hind end of the body.
* It is distinguished by the presence of small mid dorsal projection, the typhlosole, hanging into the
   lumen of the intestine. Typhlosole is poorly developed in Pheretima.
* Digested food is absorbed in this region.
3) Post-typhlosolar region :* It is the distal part of the intestine and it occupies the last 23 or  25 segments.
* It is without a typhlosole.
* It is also called rectum.
* The undigested food is converted into small pellets.
8) ANUS : It is present in the last segment. The undigested food is sent out through the anus in the form of
     pellets. These pellets are called “worm castings”.