Propels food into the stomach, controlled by the cardiac sphincter—a one-way valve at the distal end
Site for both mechanical and chemical digestion:
Churns food into small particles that become liquid when mixed with gastric juices
Stores food and slowly releases it into the small intestine
Secretes hydrochloric acid to aid in digestion; mucous cells secrete substances to coat the stomach lining; chief cells secrete pepsinogen, which is converted to pepsin to aid in digestion of protein; secretes gastrin, which stimulates secretion of acid and pepsinogen and increases gastric motility
Secretes intrinsic factor that protects vitamin B12 from stomach acid and facilitates its absorption by the parietal cells in the small intestine
Absorbs water, alcohol, and some medications
Destroys some food-borne bacteria
Allows emptying of stomach contents based on pressure gradient, a little at a time; gravity assists with emptying
5.5–6.1 m (18–20 ft) in adults
Propels contents by wormlike movements known as peristalsis
Primarily responsible for absorption of nutrients
25 cm (10 in.)
Primary site for chemical digestion
Enzymes, hormones, and bile from pancreas and liver enter and aid in absorption of nutrients:
Peptidases help break down proteins.
Enterokinase converts trypsinogen to active trypsin.
Maltase, lactase, and sucrase break down carbohydrates.
Cholecystokinin, secreted from duodenal wall, stimulates gallbladder to secrete bile.
Gastric inhibitory peptide inhibits gastric motility.
Secretin, secreted by duodenal wall, stimulates pancreatic secretions to neutralize gastric acid.
Jejunum and ileum
Jejunum: 2.4 m (8 ft)
Ileum: 3.7 m (12 ft)
Absorb water, nutrients, and electrolytes for use in body
Ascending and descending colon
1.5–1.8 m (5–6 ft)
Absorbs salt and water and excretes waste products of digestive process from the rectum (defecation)
Aids in synthesis of vitamin B12 and potassium