Digestive system III

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 stomach lumen must all be considered as potential endosenous aggressors for the epithelial lining.

Regional Differences in the Stomach Mucosa:
• The cardia is a narrow circular region ,only 1.5-3 cm in width, at the transition between the esophagus and the stomach (fig. c).
• The pylorus is the funnel-shaper region opening into the small intestine.
• The mucosa of these two stomach regions have tubular branched gland with coiled secretory portions called cardial & pylorus glands.( fig.1 c&d)
• The pits leading to these glands are longer in the pylorus .
• In both regions the glands secret mucus, as well as lysozyme; an enzyme that attachs bacterial walls.
• In the fundus &body ,the lamina properia is filled with branched, tubular gastric glands .Each gastric gland has an isthmus, a neck ,and a base ;the distribution of epithelial cells in the glands is not uniform (fig.1a&b).
The isthmus, near the gastric pit, contains differentiating mucous cells that migrate and replace surface mucous cells ,a few undifferentiated stem cells, and a few parietal( oxyntic) cells ;the neck of the glands consists of stem cells, mucous neck cells (different from the isthmus mucous cells), and parietal cells (fig.1a&b); the base of the glands contains parietal cells and chief (zymogenic) cells. Various enteroendocrine cells are dispersed in the neck and the base of the glands.