Digestive System. The group of organs which performs the function of digestion constitute digestive system.

Transcription

1 Digestive System Definition:- The active biological process by which food materials impermeable to the cell membrane is converted into permeable to the cell membrane is called digestion. The group of organs which performs the function of digestion constitute digestive system. The digestive system of earthworm includes the alimentary canal & the associated digestive glands. Alimentary Canal: - It is a long & straight tube of varying diameter, which runs through the entire length of body from mouth at the anterior end to the anus at the posterior end. It is held in position by the intersegmental septa. It has following defined regions: - 1. Mouth: - It is a crescentic aperture lying ventral to the prostomium at the anterior edge of the peristomium. 2. Buccal Chamber: - Mouth leads into a short, thin walled buccal chamber, which extends upto the middle of the third segment. Its lining is folded. A worm protrudes and retracts its buccal chamber, which acts as an organ of ingestion.

2 Alimentary canal of Earthworm 1 3. Pharynx: - The buccal chamber is followed by a stout, swollen, pear shaped & thick walled muscular chamber, pharynx, which extends upto the 4 th segment. It is externally marked off from the buccal chamber by a dorsal transverse groove, lodging the cerebral ganglia.

3 Anatomy:- Fig T. S. of alimetanary canal through Pharynx The lateral walls of pharynx are pushed inside forming a narrow horizontal shelf on each side. Thus pharyngeal cavity is divided into a dorsal or salivary chamber & a ventral or conducting chamber. The pharyngeal mass manufactures a salivary secretion from chromophil cells containing mucus & proteolytic digestive enzymes which are poured into the salivary chamber.

4 4. Oesophagus: - Behind the pharynx lies the oesophagus, or strainght, narrow, elongated & thin walled tube extending upto the seventh segment. 5. Gizzand: - The oesophaguss terminates into a prominent oval, hard, thickwalled and highly muscular organ, the gizzand, lying in the 8 th or 8 th & 9 th segment. It is lined by a tough cuticle which helps to chew the food. Its gut wall consists of only circular muscle. Fig T. S. of alimetanary canal through Gizzard 6. Stomach: - The gizzand is followed by a short narrow tube, the stomach, which extends from segments 9 to 14 with a sphincter at each end. Its walls are highly vascular & glandular & thrown into internal folds. The glandular cells secrete proteolytic enzymes. 7. Intestine: - It is a long, wide and thin walled tube extending from 15 th segment to last. The lining is ciliated folded, vascular and glandular

5 secreting proteolytic, amylolytic and lipolytic enzymes. In each segment beyond 26 th, a pair of whitish tabulated lymph glands occurs one on either side of dorsal blood vessel. It is divisible in three parts: - a) Pre-typhlosolar region: - The first part of intestine lying between segments 15 to 25, is known as the Pre-typhlosolar region. Its wall is internally folde to form minute processes or villi & is highly vascular. In the 26 th segment is given out a pair of forwardly directed lateral & conical blind outgrowth, the intestinal caeca which run upto 22 nd or 23 rd segment. These are richly vascular, internally thrown into villi like processes and secrete an amylolytic enzyme. b) Typhlosolar region: - The 2 nd part, lying between segments 26 th to 23 or 25 segments in front of anus, is termed the typhlosolar region. It is provided along its whole length with a large median dorsal and longitudinal internal fold, the typhlosole which increases the internal absorptive surface area. Fig T. S. of alimetanary canal through Typhlosolar intestine

6 c) Post-typhlosolar region: - The 3 rd part or hind part is called post-typhlosolar region or rectum, lies in last 23 or 25 segments. It has no typhlosole and opens to the exterior on the last segment by the terminal anus. 8. Anus: - It is a circular aperture place terminally in the centre of the anal segment. It is provided with a sphincter and can be closed. Food & Feeding Mechanism: - They eat the soil for the sake of decaying animal & vegetable matter contained in it. They also feed directly upon leaves, grasses, seeds, algae and other vegetation. They are nocturnal. While feeding, the muscular pharynx enlarges due to contraction of the muscles connecting the pharyngeal wall with the body wall. The buccal chamber is enlarged and the food is drawn into the mouth by the sucking action of the muscular pharynx. Digestion: - Digestion is extracellular. The passage of food in the alimentary canal is caused by peristaltic movement of the gut wall, caused by the circular and longitudinal muscles. In the pharynx, the digestive juice, containing mucin & a proteolytic ferment (enzyme), secreted by the glandular cells of the pharyngeal mass, mixes with the food. Mucin lubricates the food while ferment digests protein. There after the food passes down the oesophagus into the gizzand where it is ground up in a fine state. In the stomach the food receives the proteolytic enzymes and calcium secreted by calciferous glands. Calcium neutralizes the acidity of soil.

7 In the intestine the food is mixed with pepsin, trypsin, amylase cellulose, lipase etc. which bring about the digestion of proteins, starch, cellulose, fats, oils etc. Absorption: - The digested food is absorbed by the typhlosolar intestine and passed into the blood stream foe distribution to the various parts of the body. Egestion: - Undigested food and soil are consolidated inside the rectum and egested through anus in the form of worm castings which consists of distinct, small and rounded pellets or balls.