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SMALL INTESTINE SMALL INTESTINE Terminal part of GIT before it opens into the large intestine. 4 – 6 meters in length. Absorption – main function Divided into 3 parts: Duodenum Jejunum Ileum FEATURES FAVOURING ABSORPTION Extremely long – permits prolonged contact between food and enzymes and also digested products and absorptive cells Plicae circularis OR Valve of Kerkring – permanent folds of mucous membrane unlike rugae Villi on plicae circularis Microvilli on the enterocytes – cytoplasmic extensions GENERAL HISTOLOGICAL PATTERN OF GIT From inwards out 4 layers are present: 1. Mucosa 2. Sub mucosa 3. Muscularis externa 4. Serosa OR Adventitia GENERAL HISTOLOGICAL PATTERN OF GIT 1. i. ii. iii. From inwards out 4 layers are present: Mucosa- consists of : Lining epithelium – simple columnar cells with striated border. Layer of connective tissue- lamina propria Muscularis mucosa- smooth muscles All the above are thrown into folds called ‘villi’ 2. Sub mucosa- loose areolar tuissue 3. Muscularis externa – inner circular and outer longitudinal smooth muscles 4. Serosa OR Adventitia MUCOSA Lining epithelium – Absorptive enterocytes Goblet cells - mucous secreting Paneth cells – basally placed exocrine serous cells having zymogen granules. 4. Argentaffin cells - stimulates smooth muscles by secreting 5 HT. 5. Crypts of Liberkuhn – invagination of lining epithelium forming simple tubular glands. Basal cells are proliferating cells. 1. 2. 3. Lamina propria – connective tissue containing blood vessels and lymphoid nodules. Muscularis mucosa – smooth muscle layer contraction of which results in mixing of food. DUODENUM C shaped initial smallest portion of the small intestine Connects stomach to jejunum Villi – long, broad, leaf like and numerous Lamina propria- crypts of Lieberkuhn(STRAIGHT TUBULAR GLANDS) Sub mucosa – Brunners gland: The identifying feature of duodenum are mucous acini (tubulo alveolar glands) whose duct open into crypts of liberkuhn. The secretion contains bicarbonate and mucous. Lymphatic nodules are also seen sometimes. JEJUNUM Connects duodenum to ileum Follows the basic histological pattern of GIT Villi are smaller and less numerous Goblet cells increase in number Solitary lymph nodules present ILEUM Connects jejunum to large intestine Fingerlike, smaller and fewer villi Much more goblet cells seen Payer’s patches in the sub mucosa also called intestinal tonsils are the identifying features. IDENTIFICATION OF DUODENUM, JEJUNUM AND ILEUM DUODENUM JEJUNUM ILEUM Large, broad, leaf like villi Finger shaped villi. Fewer, shorter and irregular villi. Goblet cells in large numbers Brunners gland in sub mucosa LARGE NUMBER OF Payer’s patch in sub mucosa GOBLET CELLS in mucosa INTRINSIC NERVE SUPPLY Myenteric plexus of Auerbach in muscularis externa. plexus of Meissner’s – in the sub mucosa.