Zoology Assignment Help >> Stomach, Small Intestine, Large Intestine

STOMACH

Special features are-

1. Serosa is present and composed of peritoneum and subserous stratum of areolar connective tissue.

2. Muscular coat is thickest in all parts of alimentary canal.

3. Additional muscle layer of oblique muscle fibres is found. The sequence of thickness of these layers is -

Oblique -> Longitudinal -> Circular

4. In empty stomach its walls are folded and form rugae.

5. Muscular is mucosa is poorly developed.

6. The folds of mucous membrane along with lamina propria form tubular gastric glands in lamina propria. Average human stomach has about 35 millions of glands.

7. Goblet cells and villi are absent.

8. A typical gastric gland has four types of cells-

(i) Peptic cells or zymogenic cells-They secrete propepsin and prorenin.

(ii) Oxyntic cells or parietal cells¬ - They secrete HCI.

(iii) Mucous neck cells - They secrete alkaline mucous.

(iv) Argentaffin cells - Their function is uncertain. Typically gastric glands are of three types-

(i) Cardiac glands in cardiac part.

(ii) Fundic glands in fundic part.

(iii) Pyloric glands in pyloric part-

These glands secrete hormone called gastrin.

SMALL INTESTINE

1. Walls of duodenum are thicker than ileum.

2. Sub-mucosa is raised up into low circular folds which are called as plicae circulares or valves of kerkrings. They are permanent and not obliterated by distention. They retard the passage of food apart from increasing surface area of absorption.

3. Duodenum contains Brunner's glands. They secrete alkaline mucous.

4. Jejunum contains intestinal glands or crypts of Lieberkuhn. They are tubular glands and secrete digestive enzymes and mucous.

5. Epithelial layer deep in crypt has a very high mitotic activity. Due to this, the entire epithelial lining of small intestine is shed-off every two to four days.

6. Intestinal glands contain three types of cells viz. - enterochromoffin cells, zymogenic cells and undifferentiated epithelial cells.

7. Mucous membrane of small intestine contains lymph nodules called Peyer's patches.

8. Circular folds are less in number in ileum.

9. Villi are finger shaped and abundant in ileum while in jejunum, they are tongue shaped.

10. Brunner's glands are absent in ileum.

11. Thickness sequence of muscular layer in small intestine is-

Oblique -> Circular -> Longitudinal LARGE INTESTINE

1. It extends from ileocoecal junction to anus.

2. In caecum and colon, longitudinal muscle layer is thickened along three lines. These three ribbon like bands are called taeniae coli. Due to these taeniae, the colon is puckered and sacculated. These sacs are called haustra.

3. Small bags of peritoneum over the surface of large intestine are called appendices epiploicae. They are filled with fatty substances.

4. Crypts of Lieberkuhn and Peyer's patches both are found in colon.

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