Mrs. Dalia Kamal Eldien MSC in Microbiology

 Review to the digestive system organs  Structure and function of the stomach  Structure and function of the small intestine

 The stomach is an expandable, muscular bag, and it keeps swallowed food inside it by contracting the muscular pyloric sphincter.  Food starts to be digested and absorbed in the stomach, although absorption is mostly limited to water, alcohol and some drugs.  Food is broken down chemically, by gastric juice, and mechanically, by contraction of the three layers of smooth muscle in the muscular external layer.  The broken up food at the end of this process is called chyme.

Gastric juice is secreted by gastric mucosal glands, and contains:  Hydrochloric acid  Mucus  Pepsin: proteolytic enzymes, breaks down proteins  Lipase: digest triglycerides  Two sphincters keep the contents of the stomach:  lower esophageal sphincter between esophagus & stomach  pyloric sphincter dividing the stomach from the small intestine.

The stomach is divided into four sections, each of which has different cells and functions. Cardia Where the contents of the esophagus empty into the stomach, it contains mucous secreting glands Fundus Formed by the upper curvature of the organ, it contain the gastric glands Body or Corpus The main, central region, the epithelium of the mucosa of the and body forms invaginations called gastric pits. The lamina propria contains gastric glands, which are responsible for the synthesis and secretion of the gastric juice. Pylorus The lower section of the organ that facilitates emptying the contents into the small intestine.

 The fundus and body are identical in microscopic structure.  Only three histologically distinct regions are recognized.  The wall in all regions of the stomach is made up of all four major layers :  Mucosa  Submucosa  Muscularis  serosa

Together, these folds provide a huge surface area for absorption. Between the villi there are crypts, called crypts of Lieberkuhn, which extend down to the muscularis mucosae, they are a short glands.

1. Absorptive cells: absorb digested food 2. Enteroendocrine cells: Produce hormone

3. Goblet cells (unicellular glands) :  interspersed among absorptive cells  secrete mucus.  These cells increase in number from duodenum to rectum.

Brunner glands:  Present only in the duodenum.  Produce an alkaline fluid that protects the duodenal epithelium from the acidic.