digestion

parietal cells secrete

HCl

goblet cells secrete

mucus

chief cells secrete

pepsinogen

duodenum is a

segment of the small intestine; mixing bowl for chyme & digestive secretions of the pancreas and liver

jejunum is a segment of the

small intestine; bulk of chemical digestion & absorption

ileum isa segment of the

small intestine; absorption of water, electrolytes, and bile salts

cholecystokinin (CCK)

inhibits gastric motility

somatostatin

inhibits gastrin release

cephalic phase: control of gastric function by

the brain involves the vagus nerve; conditioned stimuli (sight & smell of food) can evoke gastric secretion

cephalic phase: activation of the vagus nerve can stimulate

HCl & pepsinogen secretion; direct stimulation of parietal & chief cells; vagus stimulation of G cells → stimulates parietal & chief cells

the cephalic phase can last

~30 minutes into the meal

gastric phase: food into the stomach stimulates the gastric phase

distention of the stomach; chemical nature of chyme, short polypeptides stimulation G cells, resulting in HCl & pepsinogen release

gastric phase: the amount of acid secreeted is closely

matched to the amount of protein ingested

gastric phase": secretion of HCl is also regulated by negative

feedback mechanisms; a decrease in pH inhibits release of gastrin

intestinal phase: gastric phase is inhibited when food

enters the small intestine; arrival of food into the duodenum sets up a neutral reflex that inhibits gastricmotility & secreetion

intestinal phase: a number of hormones may be released and

in turn inhibit gastric function (cholecystokinin (CCK) & somatostatin

each villus contains an extensive network of

capillaries and a lymphatic capillary (lacteal)

lacteals assemble fatty acids into protein-lipid packages and

carry them to the venous circulation via the left subclavian vein

esophagus is a portion of the GI tract that connects the

pharynx to the stomach; contains both skeletal and smooth muscle

esophagus: wavelike contraction of circular and

longitudinal smooth muscle moves food toward the stomach

two major types of contractions occur in the

small intestine; peristalsis & segmentation

peristalsis is much weaker in the

small intestine compared to the esophagus and stomach; slow transit of chyme through the small intestine

segmentation:muscular constrictions of the lumen which occur

simultaneously at different intestinal segments; this action mixes the chyme more thoroughly