digestive system 2
villi
center of these contain blood capillaries and lacteal (Lymphatic capillaries) surface area for digestion and absorption are about 300 m2
3 phases of the stomach
cephalic, gastric, intestinal
CCK
cholecystokinin, decrease motlility; secreted by small intestine
ileum of small intestine
contain peyers patches
bile
contains excess cholesterol, bilurubin, and bile salts
gastric motility
contractions of muscularis, mixes food with secretions through mechanical digestion and then empties into the small intestine
microvilli
contribute to surface area, extensions of membrane on apical surface of epithelial cells, extend into lumen, containing enzymes and transport proteins (brush border)
emulsify
convert a large fat globule into much smaller fat droplet
functions of small intestine
digestion and absorption; Digestion is mechanical due to motility of muscularis=segmentation
neural response
enterogastric reflex; tightens pyloric sphincter, decreases gastric motility
cephalic phase
preparation to eat or currently eating; can be triggered by visual, smell, taste; small increase in gastric secretions, small increase in motility; under neural control from ANS and hypothalamus
production of HCL
produces acidic environment, softens/denatures proteins, prevents bacterial growth and spoilage of stored food
liver/gallbladder
regulated by ANS and CCK in response to low ph in the duodenum; triggers release of bile
pancreas
regulated by stretch in wall of small intestine and low ph. detects food in duodenum
gastric glands/parietal cells
secrete HCL and intrinsic factor; convert CO2 and H20 into H2C03;
mucosal cells
secrete a thick layer of mucus as a protective barrier on the surface of epithelial lining; is alkaline so its neutralizes pH across the surface, blocks digestive enzymes from damaging epithelial cells
enteroendocrine cell
secrete the hormones CCK, GIP, secretin
Gastrin
secreted by G cells, targets the stomach, increases the secretion of gastric glands, and increases gastric motility
gastric lipase
secreted by chief cells, begins digestion of lipids
pepsinogen
secreted by chief cells, inactive form is zymogen; once its secreted into stomach lumen, it is activated at low PH into pepsin which digests proteins and breaks peptide bonds
intrinsic factor
secreted by parietal cells, enhances absorption of vitamin B12 in small intestine
GIP
secreted by small intestine; gastric inhibiting peptide, decreases motility and gastric secretions
liver/gallbladder
secretes bile around 700 ml/day. produced by liver, secreted in gallbladder
pancreas
secretes enzymes into duodenum, 1.5 l/day of pancreas juices
paneth cell
secretes lysozyme and are capable of phagocytosis
chief cells
secretes pepsinogen and gastric lipase
G cells
secretes the hormone gastrin into surrounding blood vessel
mucosa
simple columnar, mucous cells secrete mucus
intestinal inhibition
slows down stomach so that it empties slowly, may take 40 minutes to several hours to empty
small intestine of muscularis
2 layers of smooth muscle
muscularis of stomach
3 layers of smooth muscle
intestinal glands
folds at base of villi containing secretory cells goblet cells; secrete mucus
gastric phase
food enters the stomach; there is a stretch in the stomach wall, chemoreceptors detect food; under parasympathetic fibers that stimulate increase motility of secretions, increase amount of gastrin; increased motility causes chyme to press against pyloric sphincter in waves
secretin
inhibits gastric secretions; secreted by small intestine
intestinal phase
inhibits stomach as food/chyme enters small intestine; stretches wall of small intestine, chemoreceptors detect food particles; hormones are secreted
absorption across stomach
limited to H20, ions, alcohol and aspirin
micelle
lipid droplet coated with bile salts
brush border enzymes
microvilli contain enzyme bound to this membrane; its the final stage of digestion; particles are digested into small enough compounds to be absorbed
chemical digestion of small intestine
mucosa of small intestine secretes 2 L a day of water ions, and mucus. facilitated by gallbladder and pancreas
small intestine of duodenum
mucus glands called brunners gland
functions of the stomach
storage of food/large meal, digestion of food liquified into chyme, gastric secretions
examples of brush border enzymes
sucrase, peptidase, lipases, nucleases
digestive enzymes
trypsinogen, trypsin, protease, lipases, amylases, nucleases, proteases
peristalis of small intestine
wave passing down length of intestine, moves bolus of chyme a few on the downstream; motility is triggered by stretch in wall of small intestine, and also chemoreceptors detecting food in small intestine
