table 24.3 summary of digestive activities in stomach

structures

mucosa

muscularis

pyloric sphincter

mucosa structures

surface mucous cells and mucous neck cells

parietal cells

chief cells

g cells

surface mucous cells and mucous neck cells activity

secrete mucus

absorption

surface mucous cells and mucous neck cells result

forms protective barrier that prevents digestion of stomach wall

absorption- small quantity of water, ions, short-chain fatty acids, and some drugs enter bloodstream

parietal cells activity

secrete intrinsic factor

secrete hydrochloric acid

parietal cells result

intrinsic factor needed for absorption of vitamin B12 (used in red blood cell formation, or erythropoietis)

hydrochloric acid kills microbes in food, denatures proteins, converts pepsinogen into pepsin

chief cells activity

secrete pepsinogen

secrete gastric lipase

chief cells result

pepsinogen - pepsin (activated form) breaks down proteins into peptides

gastric lipase- splits triglycerides into fatty acids and monoglycerides

g cells activity

secrete gastrin

g cells result

stimulates parietal cells to secrete HCl and chief cells to secrete pepsinogen

contracts lower esophageal sphincter, increases motility of stomach, and relaxes pyloric sphincter

muscularis activity

mixing waves (gentle peristaltic movements)

muscularis result

churns and physically breaks down food and mixes it with gastric juice forming chyme

forces chyme through pyloric sphincter

pyloric sphincter activity

opens to permit passage of chyme into duodenum

pyloric sphincter result

regulates passage of chyme from stomach to duodenum

prevents backflow of chyme from duodenum to stomach