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