Digestive system III ppt.

Department of Anatomy &Histology Dr.Raja Ali

Digestive System
Stomach:
• The stomach is a muscular dilation of the digestive tract where mechanical and chemical digestion occurs.
• It is mixed exocrine - endocrine organ that digests food and secretes hormones .
• Gross inspection reveals four regions: cardia, fundus, body and pylorus (fig.1 ). The fundus and body are identical in microscopic structure.
• The mucosa and submucosa of the empry stomach have longitudinally directed folds known as rugae, which flatten when the stomach is filled with food.
• At the esophago-gastric junction, the mucosa of the stomach consists of a simple columnar surface epithelium that invaginates into the lamina propria , forming gastric pits (fig.1 ).
• Emptying into the gastric pits are branched ,tubular glands characteristic of the stomach regions (cardiac, gastric, and pyloric).
• Stem cells for the entire epithelial lining of the stomach are located in the upper regions of these glands near the gastric pits.
• The vascularized lamina propria that surrounds and supports these pits and glands contains smooth muscle fibers and lymphoid cells.
• Separating the mucosa from the underlying submucosa is a layer of smooth muscle, the muscularis mucosae .
• The epithelium covering the surface and lining the pits is a simple columnar
• epithelium, the cells of which produce a protective mucus layer.
• The mucus firmly adherent to the epithelial surface is very effective in protection. while the superficial luminal mucus
• layer is more soluble, partially digested by pepsin and mixed with the luminal contents. Hydrochloric acid, pepsin ,lipases ,and bile in the