(b) Stomach s function 1. Dilution of food materials 2. Acidification of food (absorption of dietary Fe in small intestine) 3. Partial chemical digest

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Lionel McCarthy
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1 (1) General features a) Stomach is widened portion of gut-tube: between tubular and spherical; Note arranged of smooth muscle tissue in muscularis externa. 1

2 (b) Stomach s function 1. Dilution of food materials 2. Acidification of food (absorption of dietary Fe in small intestine) 3. Partial chemical digestion of proteins continued digestion of carbohydrates 2

3 4. Little to no absorption under normal conditions a. Can absorb glucose b. Absorbs ethanol c. Absorbs Na + and K +, but only if levels of these ions are subnormal d. Absorbs water when body dehydrated and osmotic pressure abnormally high and blood volume and pressure unusually low. 5. Formation of acidic chyme: Mixture of acidic gastric juice and food 3

4 (c) Mucosa: very folded; folds longitudinally oriented and called rugae. 1. Lumenal epithelium: simple columnar epithelium: secretes mucus; cytoplasm tends to be acidophilic; cells lack microvilli. 2. Lumenal surface has abundant pits: funnel-like depressions that lead to the mucosal glands; pits vary in steepness and depth from one region of organ to another. 4

5 3. Mucosal glands common compound (branched) tubular glands extending into deeper parts of mucosa, from pits; not acinar wall of gland one cell thick 4 possible cell types mucous cells parietal cells chief (principal; peptic) cells endocrine cells (G cells). 5

6 a. Except for endocrine cells, restricted to one region of stomach, glands are exocrine, secreting fluid into lumen of stomach b. All cells of wall of gland are glandular cells. c. Uppermost part of gland, continuous with epithelium of pit; neck of gland neck composed of low columnar mucus cells - not as eosinophilic as lumenal epithelial cells mucus neck cells. f. Stomach. 6

7 d. Below neck of gland, cells include the other 3 types. (1) Parietal cell: large, spherical, eosinophilic, sometimes granular cytoplasm; secretes HCl: acidification of the food; often found in upper part of gland. 7

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(2) Chief (principal; peptic) cell tends to be in lower part, narrower than parietal cell cytoplasm basophilic nucleus toward basal side of cell very active in protein synthesis: produces and

10 (2) Chief (principal; peptic) cell tends to be in lower part, narrower than parietal cell cytoplasm basophilic nucleus toward basal side of cell very active in protein synthesis: produces and secretes pepsinogen zymogen of pepsin: enzyme that breaks protein molecules into chains of several to many amino acid residues. (a) Chief cells therefore are zymogenic cells. (b) Pepsinogen converted to pepsin in lumen of gland and in lumen of organ. 10

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12 (3) Endocrine cells: specifically gastrin cells, for the hormone they produce and release restricted to deepest parts of glands of one region of stomach. A subset of enteroendocrine cells; >12 types gastrin, histamine, endorphins, serotonin, cholecystokinin, somatostatin 12

13 4. Muscularis mucosae present, composed of smooth muscle tissue, often in 3 layers; has numerous thin extensions up into lamina propria. 5. Lamina propria composed of unusually cellular dense C.T. with capillaries, arterioles, venules, lymphatic capillaries, small nerves; all of these but capillaries very difficult to detect MM 13

14 (d) Submucosa 1. Extends up into rugae. 2. Mostly dense C.T small muscular arteries, small veins, smaller blood vessels, small lymphatic vessels, small masses of neural tissue and sometimes clumps of adipocytes areas of loose C.T. may be present also. f. Stomach Mucosa Submucosa MM Muscularis externa 14

15 (e) Muscularis externa of stomach 1. Normal Inner-circular, outer-longitudinal organization partially lost: smooth muscle tissue is in large slabs oriented in a variety of directions, some remnant of inner-circ., outer-long pattern usually detectable. Inner circular Outer longitudinal 15

16 2. Myenteric plexus usually detectable; its location indicates the original interface between inner-circ, outer-long layers. 3. This organization of smooth muscle tissue relates to the organ's shape. 4. Muscularis is, overall, relatively thick and powerful. Myenteric plexus 16

17 (f) Tunica adventitia 1. T. adventitia of stomach is distinct layer with an outer, mesothelium, covering. 2. T. adventitia composed of dense C.T. and loose C.T. and contains larger blood vessels and nerves than those found in submucosa. T.adventitia 17

18 g) Stomach regions divided into 4 regions; in most cases these regions differ in mucosal structure only. 1. Cardiac region: small region adjacent to cardiac sphincter. 2. Fundic region (fund: root meaning deep): one side of upper part of organ. 3. Body: most of organ. 4. Pyloric region: lower end, adjacent to pyloric sphincter. 18

19 2) Special features of region of stomach (a) Cardiac region 1. pits; intermediate depth and cardiac glands are almost entirely mucus cells 2. Glands sometimes not as densely packed as in other regions. 19

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(b) Fundic region and body (no histological differences between them) 1. Pits relatively shallow (because fluid secreted by glands is nonviscous) 2.

21 (b) Fundic region and body (no histological differences between them) 1. Pits relatively shallow (because fluid secreted by glands is nonviscous) 2. Gastric glands densely packed; C.T. of lamina propria not obvious. Neck of gland composed of mucus neck cells; other cells of gland parietal cells and chief cells 21

22 (c) Pyloric region 1. Pits deep half the depth of the mucosa Gland composed of mucus cells ;look like mucus neck cells diameter of gland's lumen high, due to high viscosity of secreted fluid Called pyloric glands. f. Stomach 22

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24 a. Pyloric region and cardiac region; major function; mucus production; mucus coating of the lumenal epithelium protection from acidity and proteolytic action of gastric juice. If mucus layer becomes thin or lost, the pepsin and HCl in the lumen will destroy the lumenal epithelium of that area and perhaps begin destroying the glands and C.T. of the lamina propria Called a peptic ulcer. 24

25 b. Lower parts of the pyloric glands ; cells are mainly endocrine; with H&E staining they are not distinguishable from mucus cells gastrin endocrine cells produce the hormone gastrin, controls gastric glands gastrin is released to the capillaries of the lamina propria rather than to the lumen of the gland. c. Overall length of glands relatively great 25

26 3. Mucosa unusually thick overall; staining relatively pale. 4. Pyloric region ends at pyloric sphincter; between stomach and duodenum sphincter itself is a thickened region of inner, circular layer of muscularis externa. 26

` Regions Cardiac Fundus/ body Pyloric Pits Intermediate depth Shallow Deep, at least 1/2 of mucosa with wide lumen Glands Not densely packed obvious lumen Densely packed Not densely packed obvious

27 ` Regions Cardiac Fundus/ body Pyloric Pits Intermediate depth Shallow Deep, at least 1/2 of mucosa with wide lumen Glands Not densely packed obvious lumen Densely packed Not densely packed obvious lumen Gland cells Mucus Mucus, parietal, chief, enteroendocrine cells (not visible w H&E) Mucus enteroendocrine cells (not visible w H&E) Function Protection of cardiac region and distal esophagus Production of gastric juice; Hormone regulation Protection of pyloric region Hormone regulation 27

Alimentary Canal (I)

Alimentary Canal (I) Esophagus and Stomach (Objectives) By the end of this lecture, the student should be able to discuss the microscopic structure in correlation with the function of the following organs: