Stomach Temporary storage tank Chemical breakdown of proteins

Stomach • Temporary “storage tank” • Chemical breakdown of proteins begins and food is converted to chyme • Chyme: creamy paste • ~ 6 -10 inches long • Empty volume of 50 m. L • Full can hold up to 4 L (1 gallon) of food and may extend nearly all the way to the pelvis!

Stomach • Circular, longitudinal, and oblique smooth muscle layers – allows for stomach to churn, mix, pummel food physically breaking it down – Move food along the digestive tract

Stomach – Regions • Cardiac region – Cardia “near the heart” – Surrounds the cardiac sphincter • Fundus – Dome-shaped part, tucked beneath the diaphragm – Superior bulge • Body – midportion

Stomach – Regions • Pyloric region – Funnel shaped region near the pyloric sphincter • Pyloric sphincter – Exit of the stomach to the small intestine

Stomach – Regions • Rugae (wrinkle, fold) – seen when stomach is empty inward collapse to form large, longitudinal folds • Greater curvature – Convex, lateral surface • Lesser curvature – Concave, medial surface

Stomach - Regions • Lesser omentum – – Helps to keep the stomach connected to other digestive organs and the body wall – Runs from liver to lesser curvature

Stomach - Regions • Greater omentum – – Helps to keep the stomach connected to other digestive organs and the body wall – Runs from greater curvature to cover the small intestine, spleen, and large intestine – Riddled with fat deposits (oment = fatty skin)

Stomach • Lining is simple columnar tissue with goblet cells • produce a protective coat of mucus • Also dotted with gastric pits (small openings) which produce gastric juice • hydrochloric acid and pepsinogen (inactive) – Release gastric juice = pepsinogen + HCl – pepsin (enzyme) • Pepsin + proteins digestion!

Stomach • Mucous coats the inside of the stomach to protect it from HCl and pepsinogen. • Churning of food and mixing makes chyme – Contains fats, sugars, starches, vitamins, minerals, proteins, and amino acids.

Stomach • The secreted HCl (hydrochloric acid) makes the stomach very acidic • (p. H 1. 5 – 3. 5) – Necessary for activation and optimal activity of pepsin which digests proteins – Aids in food digestion denatures proteins, breaks down cell walls of plant foods, kills many of the bacteria that are ingested with foods

Ulcers • When the mucus barrier is breached and underlying tissue is damaged • erosion of the stomach wall • Very painful. Usually starts 1 -3 hours after eating. Relieved by eating again. • Danger if ulcer perforates the stomach wall and stomach contents leak into the abdominal cavity • Thought to be caused by taking aspirin, ibuprofen, smoking, spicy foods, alcohol, coffee, stress • Most recurrent ulcers are caused by Helicobacter pylori bacteria, but it is hard to prove this because it is found in most healthy people

Stomach • Food is forced out of the stomach by peristalsis through the pyloric sphincter and into the duodenum.

Small Intestine • The body’s major digestive organ • Digestion is completed and virtually all absorption occurs. • Starts at the pyloric sphincter and extends to the ileocecal valve. • Longest portion of the digestive tract 7 -13 feet while alive and ~20 feet in a cadaver. • Changes are because of loss of muscle tone when deceased. • Diameter ranges from 2. 5 – 4 cm (1 -1. 6 in)

Duodenum • Literally means “ 12 finger widths long” • About 10 inches long. • Only (and last) place where digestive juices enter.

Duodenum • Shortest section but contains: – Bile duct delivers bile from liver – Main pancreatic duct carries pancreatic juice from pancreas – Hepatopancreatic ampulla where the two connect and then open into the duodenum via the major duodenal papilla

Jejunum and Ileum • Jejunum (“empty”) 8 ft • Ileum (“twisted”) 12 ft • Hang in sausage like coils in the central and lower part of the abdominal cavity • Highly adapted for nutrient absorption. Three structures increase the surface area to the size of a tennis court (250 m 2).

Jejunum and Ileum 1)Plicae circulares deep, permanent folds of the mucosa and submucosa. • These folds force chyme to spiral through the lumen, slowing its movement and allowing time for full nutrient absorption

Jejunum and Ileum 2)Villi – “tufts of hair” finger like projections of the mucosa (1 mm), that give it a velvety texture (like the nap of a towel). • The Villi are large and leaflike in the duodenum (most active absorption) and gradually narrow and shorten along the length of the small intestine

Jejunum and Ileum 3)Microvilli tiny projections of the plasma membrane of absorptive cells of the mucosa. • Give the surface a fuzzy appearance called the brush border. • The plasma membranes bear enzymes referred to as brush border enzymes that complete the digestion of carbohydrates and proteins

Jejunum and Ileum • Most absorption occurs in the proximal part of the small intestines so the Plicae circulatures, villi and microvilli decrease in number towards the distal end.

Intestinal Juice • 1 -2 liters of intestinal juice are secreted daily. • Major stimulus for its production is the distention or irritation of the intestinal mucosa by acidic chyme. • Slightly alkaline (7. 4 -7. 8) • Largely water, but also contains some mucus. Fairly enzyme poor because intestinal enzymes are limited to the bound enzymes on the brush border.