GIT 2 By: Dr Hossam El-deen Salem

Rugae Longitudinal folds of the stomach wall to allow for expansion.

Structure of stomach wall Mucosa  Epithelium: simple columnar, secreting mucus  Lamina propria: occupied by the gastric glands.  Muscularis mucosa: inner circular and outer longitudinal layers of smooth muscle Submucosa: Connective tissue Musculosa Inner oblique, middle circular and outer longitudinal layers of smooth muscles (for mixing gastric contents) Serosa Connective tissue covered with mesothelium.

Gastric glands  Simple branched tubular glands  Secrete gastric juice  Occupy the whole lamina propria down to muscularis mucosa  Lie perpendicular to the surface  Each gland is divided into 3 parts: Base: The deepest part Neck: The middle part Isthmus: The upper part  The pit is not a part of the gland. It is the duct and is covered by surface epithelium  Cells of the gland Mucus neck cell Stem cells (renewal) Parietal=oxyntic cells [Hcl] Peptic=zymogen=chief cells Enteroendocrine cells

Surface mucus cells & Mucus neck cells  Each is distended with mucous and has basal nucleus  Surface mucus cells secrete a gel-like layer of visible neutral mucus to protect the stomach lining from autodigestion. [Bicarbonate ions trapped in this layer of mucus maintain a neutral pH of the mucus despite the low (acidic) pH of the luminal contents]  Mucous neck cells produce soluble acidic mucus that is mixed with and lubricates the chyme, reducing friction as it moves along the digestive tract

Parietal cell

Parietal = oxyntic cells Structure  Intracellular canaliculi (to increase surface area for secretion)  Extraordinary number of mitochondria (active cells)  Rich in smooth endoplasmic reticulum sER (Cl metabolism)  These large number of membranes (sER, mitochondria, canliculi) makes the cell acidophilic, so they are called oxyntic cells  Lie on the wall of the gland and do not reach the lumen, so they are called parietal cells Function  Secrete H and Cl (This is better than saying secrete HCl, because both H and Cl are released in the canaliculi, then HCL is formed there (outside the cell = in the lumen)  Secrete IF (intrinsic factor): which is a glycoprotein required for absorption of vitamin B12 Q1: This is the intrinsic factor. What is the Extrinsic factor? Q2: These are factors for what? A1: B12 itself is the extrinsic factor A2: They are factors of pernicious anemia. If deficient, pernicious anemia occurs Q3: Why is it called pernicious? A3: “pernicious” means “deadly.” The condition is called pernicious anemia because it often was fatal in the past, before vitamin B12 treatments were available. Now, pernicious anemia usually is easy to treat with vitamin B12 pills

Chief cell  They have characters of protein secreting cells  columnar cells with oval basal nuclei  Have polarity: basal basophilia (rER) and apical acidophilia (zymogen granules)  well–developped Golgi complex, and numerous mitochondria  Luminal border has short microvilli (sites of exocytosis)  They secrete digestive enzymes [All enzymes are proteins] Names  The chief function of stomach is digestion. These cells secrete digestive enzymes. So they are the chief cells  An important enzyme is pepsinogen which is converted to pepsin when exposed to gastric acidity. So they are peptic cells  They generate enzymes, so the are zymogen cells

(1) These cells are in the wall of GIT (entero) and secrete hormones (endocrine) that acts mostly locally (paracrine) (2) In stomach They release the following hormones: Gastrin: promotes secretion of gastric juice and enhance gastric motility S erotonin contraction of the smooth muscles of the blood vessels. S omatostatin inhibits the release of growth hormones. E nteroglucagon increases blood sugar levels E ndorphin opiate-like Enteroendocrine cells Enteroendocrine cells: secretory granules are present basally to release in blood stream not in the lumen