Histology of gastrointestinal tract

Mbbs 2nd year08/09/2013

Digestive system consist of the digestive tract and its associated glands that helps in process of digestion.

The gastrointestinal tract is a hollow tube with lumen of variable diameter .

Wall made up of 4 layers Mucosa Submucosa Musularis Serosa

•Muscle layer : inner :circular outer longitudinal •Myenteric nerve plexus (Auerbach)

Musuclaris

•Thin layer of connective tissue Serosa

• Epithelial lining • Lamina propria • Muscularis mucosa

mucosa

• Connective tissue • Submucosal plexus of autonomic

nerve (meissner)submucosal

Stomach is divided into 4 regions : cardia , fundus , body and pylorus .

Stomach digests the food by muscular activity converting it into chyme .

The muscularis consist of three layer for mixing of stomach content and turns into chyme

Esophagogastric junction

Stomach consist of simple columnar epithelium that invaginates into lamina propia forming gastric pit .Emptyping into this pit are glands .

Regions of stomach

Glands in cardiac & pylorus

Branched tubular with coiled secretory portion Responsible for secretion of mucus and lysozyme

Body/fundus

Gastric gland

Clinical correlate :

• In case of atrophic gastritis both parietal and chief (Zymogenic/Peptic ) cell decrease in number and results in vitamin B12 deficiency .

• Pernicious anaemia , which is a disorder of erythrocyte forming mechanism is caused by lack of IF , and Vitamin B12.

Small intestine

Small intestine /duodenum

Plica circularis : mucosa &submucosa

Villi : epithelium & lamina propria

Microvilli : apical cytoplasm

Mucosa Surface epithelium : enterocytes & goblet cells Lamina propria : Muscularis : Surface epithelum & lamina propria : villi

Between villi are openings of short tubular glands : intestinal crypts or crypts of liberkuhn

Villus contain microvasculature and lymphatics called lacteals .

Intestinal gland or crypts of liberkuhn

• Goblet cells • Paneth cells • Enteroendocrine cells • Stem cells

Submucosa has large clusters of branched tubular mucous gland , the duodenal gland or brunner gland .

Pancreas

• Mixed exocrine and endocrine gland • Produces both digestive enzymes and

hormones .• Digestive enzymes : exocrine portion • Hormones : endocrine epithelial cells

Pancreatic acini

pancreas

Islet of langerhans

Alpha cells : periphery secrete glucagonBeta cells : centre , secrete insulinDelta cells : periphery , secrete gastrin and somatostatin

Clinical correlate

In acute necrotizing pancreatitis, the proenzymes may be activated and digest the whole pancreas, leading to very serious complications. Possible causes are alcoholism, gallstones, metabolic factors, trauma, infection, and drugs.

Clinical correlate

Acute pancreatitis :Damage to the pancreatic acinar cells releases pancreatic enzymes into the local tissues. These powerful enzymes cause death of pancreatic tissue and severe inflammation termed acute pancreatitis. The release of pancreatic lipase causes death of local fat cells (fat necrosis). Pancreatic amylase is released and can be detected at high levels in the blood. This is a severe life-threatening condition.