Anatomy of the Stomach

Stomach Structure

• Cardiac region surrounds the cardiac orifice
• Fundus is a dome-shaped region beneath the diaphragm
• Body is the midportion of the stomach
• Pyloric region is made up of the antrum and canal, terminating at the pylorus

Stomach Curvatures

• Greater curvature is the entire extent of the convex lateral surface
• Lesser curvature is the concave medial surface
• Lesser omentum runs from the liver to the lesser curvature
• Greater omentum drapes inferiorly from the greater curvature to the small intestine

Stomach Lining

• Mucosal lining is simple columnar epithelium with numerous tubular gastric glands
• Rugae are folds in the inner lining of the stomach

Gastric Glands

• Mucous neck cells produce a sticky alkaline mucus that traps a layer of bicarbonate-rich fluid beneath it
• Gastric glands secrete gastric juice
• Chief cells produce protein-digesting enzymes (pepsinogens)
• Parietal cells produce hydrochloric acid
• Endocrine cells produce gastrin

Gastric Juice

• The secretions of the exocrine gastric glands (mucous, parietal, and chief cells) make up the gastric juice
• The products of the endocrine cells are secreted directly into the bloodstream and are not part of the gastric juice

Small Intestine

• It is the longest section of the digestive tube
• Runs from the pyloric sphincter to the ileocecal valve
• The bile duct and main pancreatic duct join the duodenum at the hepatopancreatic ampulla

Small Intestine Sections

• The duodenum is a short section that receives secretions from the pancreas and liver via the pancreatic and common bile ducts
• The jejunum is where most of the nutrients are absorbed into the blood
• The ileum is where the remaining nutrients are absorbed before moving into the large intestine

Intestinal Absorption

• The intestines process about 2.5 gallons of food, liquids, and bodily waste every day
• In order for enough nutrients to be absorbed into the body, it must come in contact with large numbers of intestinal cells which are folded
• Each of these cells contains thousands of tiny finger-like projections called "villi" and each villus contains microscopic "microvilli"

Villi and Microvilli

• In one square inch of small intestine, there are about 20,000 villi and ten billion microvilli
• Each villus brings in fresh, oxygenated blood and sends out nutrient-enriched blood
• The villi sway constantly to stir up liquefied food and remove the nutrients which can be absorbed and then passed through the membranes of the villi into the blood and lymph vessels

Muscular Movement

• The muscles which encircle the tube constrict about seven to twelve times a minute to move the food back and forth, to churn it, knead it, and to mix it with gastric juices
• The small intestine also makes waves which move the food forward, but these are usually weak and infrequent to allow the food to stay in one place until the nutrients can be absorbed

Large Intestine

• It begins at the ileocecal junction and ends at the anus
• The saclike cecum lies below the ileocecal valve in the right iliac fossa and contains a wormlike vermiform appendix
• The large intestine has distinct regions: ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, and sigmoid colon

Large Intestine Functions

• The large intestine produces no digestive enzymes
• Chemical digestion is completed in the small intestine before the chyme reaches the large intestine
• Functions of the large intestine include the absorption of water and electrolytes and the elimination of feces

Rectum and Anal Canal

• The rectum continues from the sigmoid colon to the anal canal and has a thick muscular layer
• The last 2 to 3 cm of the digestive tract is the anal canal, which continues from the rectum and opens to the outside at the anus
• The smooth muscle layer is thick and forms the internal anal sphincter at the superior end of the anal canal, which is under involuntary control
• There is an external anal sphincter at the inferior end of the anal canal, which is composed of skeletal muscle and is under voluntary control