digestive processes

mechanical digestion in oral cavity

chewing, breaking food physically

chemical digestion in oral cavity

breaking food with enzymes, parasympathetic stimulation of serous cells/salivary gland to produce watery saliva that contains salivary amylase

another name for swallowing

deglutition

deglutition (process)

peristaltic muscle contraction moves bolus through esophagus, food passes through gastroesophageal sphincter to enter the stomach

bolus

chewed food and saliva

stimuli for release of gastric secretions

stretch of stomach increases parasympathetic input, partially digested proteins and alcohol stim release of gastrin

what is gastrin

hormone in the stomach

gastrin (actions)

stimulates chief cells, parietal cells, and smooth muscle

chief cells (action)

produce and release pepsinogen

parietal cells (action)

reason why stomach is acidic, release HCl, negative feedback as pH declines toward pH 1

smooth muscle (action)

peristaltic contractions, helps move food along

chyme

mix of gastric secretions and partially digested food, what you see when you throw up

gastric secretions

hydrochloric acid, enzymes like pepsinogen, mucus

protein digestion (chyme production)

protein denaturation, pepsinogen self activates to pepsin

absorption

few nutrients absorbed, alcohol and some drugs easily absorbed

time course for LIQUID meal

leaves stomach in 1-2 hours

time course for SOLID meal

leaves stomach in 2-3 hours

peristalsis

waves that pushes chyme toward the pyloric sphincter, then causes the sphincter to partially close, causing backsplash of chyme and mix for better digestion

what are the two hormones in hormone regulation of digestion

secretin and cholecystokinin

secretin (stimuli for release)

chyme entering the small intestine, especially PARTIALLY DIGESTED PROTEINS, acidic chyme, fats, hyper/hypotonic solutions

secretin (actions on STOMACH)

inhibits chief and parietal cells, so no pepsinogen and HCl, decreases gastric motility

secretin (actions on SMALL INTESTINES)

stims RELEASE OF PANCREATIC SECRETIONS and stims bile production by liver

cholecystokinin (stimuli for release)

chyme entering the small intestine, especially FATS and proteins

cholecystokinin (actions)

stims GALL BLADDER CONTRACTION, release of pancreatic enzymes, feelings of satiety

carbohydrates (steps)

pancreatic amylase and brush border enzymes

pancreatic amylase

breaks down starches to disaccharides

brush border enzymes

produced by small intestine cells, bound to microvilli, breaks down disaccharides to monosaccharides

proteins (actions)

pancreas releases zymogens into duodenum through pancreatic duct, brush border enzymes

lipids (actions)

bile salts emulsify fats, pancreatic lipase breaks down fats into micelles, micelles absorbed into cells of intestinal wall, intestinal cells form chylomicrons, which are secreted into lacteals and enter venous blood via thoracic duct

movement in small intestines

peristalsis, segmentation, migrating mobility complex

segmentation

mixing movement in small intestine

migrating mobility complex (MMC)

series of sustained waves that move food through small intestine, beginning of duodenum to end of ileum, takes 2 hours, cleans small intestines