Answer
Gastric mucosa. This is the innermost compartment of the wall of the stomach. It faces the lumen and is underlain by the submucosa, the muscularis, and the serosa ( the outer covering ) of the stomach. The innermost layer of the mucosa is an epithelium of simple columnar epithelial cells which sits on a lamina propria of areolar connective tissue. Underneath the lamina is the muscularis mucosae of smooth muscles.
The gastric mucosa has several types of secretory cells --surface cells and cells organized into glands.Te secretory cells include mucous cells, parietal cells, chief cells, and enteroendocrine cells, The general name for the non-endocrine glands is gastric glands but dependent on location some are given special names. Thus gastric glands which occur mainly in the cardiac region of the stomach are called cardiac glands, and those that are found mainly in the pyloric region are called pyloric glands . Gastric glands that occur in other areas of the stomach are just gastric glands.
The surface epithelial layer of the mucosa forms many narrow invaginations that descend as narrow canals into the lamina propria; these narrow, blind canals are called gastric pits; the cells that line them produce several kinds of secretions essential for carrying out of the digestive functions of the stomach , and the duodenum.
The so-called cardiac glands are located mainly in the cardia; the pyloric glands are located primarily in the pyloric region, and the gastric glands are in the other reas of the stomach. Mucous cells and mucous neck cells are found mainly in the cardiac and pyloric regions, but also in other areas of the stomach, Parietal cells are are usually found in the upper half of gastric glands. Chief cells are absent from cardiac and pyloric glands; enteroendocrine cells are found mainly in the bottom/lower ends of glands --mostly in the pyloric and gastric glands
Work Step by Step
Functions of the cells of the gastric mucosa:
1. The mucous surface cells and the mucous neck cells of the gastric glands secrete mucus. This mucous secretion protects the stomach from damage by the very low pH hydrochloric acid; it also protects the epithelial cells from self-digestion by stomach pepsin ( a protease). In addition mucous surface cells absorb small amounts of ions, short chain fatty acids and some drugs.
2, Parietal cells secrete hydrochloric acid(HCL) and intrinsic factor (IF). Intrinsic factor is necessary for the absorption of Vitamin B12, which supports erythropoiesis. Hydrochloric acid denatures proteins, converts pepsinogen ( a zymogen) to the active enzyme proteolytic enzyme pepsin.. It also creates the acid environment necessary for the enzymatic activity of pepsin. Hydrochloric acid also facilitates digestion by breaking up connective tissue and cellulase, converting ferric compounds to their ferrous forms and by helping to liquefy chyme. In addition microbes in the stomach are destroyed by HCL.
3 Chief cells secrete the zymogen pepsinogen. Gastric lipase is also produced by these cells. Pepsin digests protein and polypeptides; gastric lipase converts to fatty acids and monoglycerides. Pepsin also has an autocatalytic action on the conversion of pepsinogen to the active enzyme (pepsin).
4. G. cells secrete gastrin. This hormone stimulates the secretion of HCL by parietal cells and the secretion of pepsinogen by the chief cells. Furthermore, gastrin stimulates gastric motility , constricts the lower esophageal sphincter and also relaxes the pyloric sphincter.
5 . The enteroendocrine cells are of several kinds. They secrete hormones such as ghrelin--the appetite stimulating hormone--secretin, cholecystokinin (CCK), Substance P, GIP and VIP. which have important effects on duodenal digestion, motility and absorption.
