Stomach anatomy and histology

Ali Al-Alwani
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1. The Stomach By :- Ali Laith Al- Alwani & Saja Ali Group :-117 i-6

2. The anatomical structure Four Regions 1: Cardiac Region 2: Fundic Region( Fundus ) 3: Body(corpus) 4: Pyloric Region • Lesser curvature • Greater curvature The stomach is an expanded J-shaped organ in the upper left region of the abdominal cavity. It is continuous with the esophagus superiorly and empties into the duodenum of the small intestine inferiorly. It continues the mechanical and chemical digestion of the bolus. After the bolus has been completely processed in the stomach, the product is called chyme.

3. Functions of Stomach Digestion. Produce acid. Reservoir for food. Slows food entering intestines. Help with vitamin absorption (Vitamin B12). And also The stomach is responsible for the formation and processing of the ingested food into a thick acidic fluid known as chyme.

4. Gastric Histology The ensuing discussion of the stomach details the fundic ,because the microscopicanatomy of each of the remaining regions is a variation of that of the fundic region Fundic Mucosa

5. FUNDIC GLANDS The simple columnar epithelium constituting the fundic gland is composed of six cell types:- (1) surface-lining cells, (2) mucous neck cells, ( 3) regenerative (stem) cells, (4) parietal ( oxyntic ) cells, ( 5) chief ( zymogenic ) cells, ( 6) diffuse neuroendocrine system (DNES) cells

6. Mucous Neck Cells are columnar and resemble surfacelining cells. Thus, they have short microvilli , basally located nuclei, and a well-developed Golgi apparatus and rough endoplasmic reticulum (RER) .Their mitochondria are located mainly in the basal region of the cell. The apical cytoplasm is filled with secretory granules containing a homogeneous secretory product , which differs from the mucus synthesized by this mucus is soluble and functions to lubricate the gastric contents. The lateral membranes oaf mucous neck cells form zonulae occludentes and zonulae adherentes with the surrounding cells.

7. Regenerative (Stem) Cells These columnar stem cells do not have many organelles but do have a rich supply of ribosomes . Their nuclei are basally located, have little heterochromatin, and display a large nucleolus. The lateral cell membranes of these cells also form zonulae occludentes and zonulae adherentes with those of neighboring cells. Regenerative cells proliferate to replace all of the specialized cells lining the fundic glands, gastric pits, and luminal surface. Newly formed cells migrate to their new locations either deep into the gland or up into the gastric pit and gastric lining. Surface-lining cells, DNES cells, and mucous neck cells are replaced every 5 to 7 days; thus, regenerative cells have a high proliferative rate .

8. Parietal ( Oxyntic ) Cells Large, round to pyramid–shaped parietal cells are located mainly in the upper half of the fundic glands and only occasionally in the base. These cells produce hydrochloric acid ( HCl ) and gastric intrinsic factor Their most remarkable characteristic is the invaginations of their apical plasmalemma to form deep intracellular canaliculi lined by microvilli . The cytoplasm bordering these canaliculi is richly endowed by round and tubular vesicles, the tubulovesicular system. Additionally, parietal cells are rich in mitochondria, whose combined volume constitutes almost half that of the cytoplasm. The protein synthetic apparatus, the RER and the Golgi apparatus, are present but only to a limited extent.

9. Chief ( Zymogenic ) Cells Most of the cells in the base of fundic glands are chief cells. These columnar cells display a basophilic cytoplasm, basally located nuclei, and apically situated secretory granules that house the proenzyme pepsinogen (as well as rennin and gastric lipase ). Electron micrographs of chief cells exhibit a rich supply of RER, an extensive Golgi apparatus, and numerous apical secretory granules interspersed with a few lysosomes . Short , blunt, glycocalyxcovered microvilli project from the apical aspect of the cell into the lumen of the gland.

10. DNES Cells (APUD or Enteroendocrine Cells) DNES cells may be open or closed. They manufacture endocrine, paracrine , and neurocrine hormones. A group of small cells that are individually dispersed among the other epithelial cells of the gastric mucosa are known collectively by several names: Argentaffin and argyrophilic cells, because they stain with silver stains APUD cells, because some of them can take up the precursors of amines and decarboxylate them DNES cells, because they are members of the diffuse neuroendocrine system of cells. Enteroendocrine cells because they secrete hormone-like substances and are located in the epithelium of the enteric (alimentary) canal . BM, basement membrane ; G, Golgi apparatus; L, lumen ; m, mitochondria; N, nucleus; nu , nucleolus; rER , rough endoplasmic reticulum ; ZC, zymogenic (chief) cell; zg , zymogen granules;. (From Karam SF , Leblond CP: Identifying and counting epithelial cell types in the “ corpus” of the mouse stomach. Anat Rec

11. Muscularis Mucosae of the Stomach The smooth muscle cells that compose the muscularis mucosae are arranged in three layers. The innercircular and outer longitudinal layers are well defined; however, an occasional third layer, whose fibers are disposed circularly (outermost circular), is not always evident.

12. Differences in the Mucosa of the Cardiac and Pyloric Regions

13. Submucosa of the Stomach The dense, irregular collagenous connective tissue of the gastric submucosa has a rich vascular and lymphatic network that supplies and drains the vessels of the lamina propria . The cell population of the submucosa resembles that of any connective tissue proper. The submucosal plexus is in its accustomed location, within the submucosa in the vicinity of the muscularis externa . Muscularis Externa The smooth muscle cells of the gastric muscularis externa are arranged in three layers. The innermost oblique layer is not well defined except in the cardiac region . The middle circular layer is clearly evident along the entire stomach and is especially pronounced in the pyloric region, where it forms the pyloric sphincter. The outer longitudinal muscle layer is most evident in the cardiac region and the body of the stomach but is poorly developed in the pylorus. The myenteric plexus is located between the middle circular and outer longitudinal layers of smooth muscle. The serosa of the stomach is as described above for the alimentary canal in general. It is continuous with the parietal peritoneum of the abdominal cavity via the greater omentum and with visceral peritoneum of the liver at the lesser omentum . Otherwise , it exhibits no special features.