Lecture 4: A &P of digestive system pt 2 Flashcards
cephalic phase of the stomach
- smell or thought of food causes parasympathetic stimulation of vagus nerve, which innervates the stomach
- in response cell in stomach release mucus, HCl, pepsinogen, ghrelin, and gastrin.
gastric phase of the stomach
- begins w arrival of food in stomach
- more gastrin is released into the blood, which leads to protein digestion, mixing wave contractions, and stimulates gastric motility
- gastric lipase digests fats
- protein called intrinsic factor binds to b12 for b12 absorption
function of HCl in stomach
- acidic environment necessary for cells that secrete pepsinogen
- kills most food pathogens
- denatures proteins for further breakdown
- inactivates food enzymes as well as salivary amylase
- breaks down plant cell walls and meat connective tissue
rate of gastric emptying: increased volume of food
increased rate (activation of stretch receptors and increased pressure)
rate of gastric emptying: increased osmality
lowered rate (osmosis has to happen first)
rate of gastric emptying: increased nutrient density
lowered rate
rate of gastric emptying: increased food particle size
lowered rate (heavier particles collect in lower part of stomach and have to be broken down)
rate of gastric emptying: increased food viscosity
lowered rate (soluble fiber means more water has to be drawn in)
dietary fibers
- carbohydrate polymers with ten or more units that can’t be digested by humans
- bacteria in colon breaks it down into SCFAs
- reduces risk of colon cancer
insoluble fiber
- found in plant skins, main component of plant cell wall
- swells in water
- reduce transit time in GI tract because it gives bulk to stool and helps with constipation
soluble fiber
- inner fleshy part of fruits and endosperm of grains and seeds
- thickens in water, increases viscosity
- slows gastric emptying, increases satiety
- binds to bile for elimination, reduces level of circulating cholesterol
- slows glucose absorption rate and increases insulin sensitivity, aids diabetics
ulcer
when stomach acid damages lining of digestive tract.
-causes: specific bacteria, anti-inflammatory pain medications like aspirin
intestinal phase
- begins when chyme first enters the duodenum
- controls emptying and secretions in GI tract
reactions to distention of duodenum
- inhibits gastrin production
- inhibits gastric contractions
- stimulates contraction of pyloric sphincter (prevents further discharge of chyme into small intestine till it’s good and ready)
intestinal phase secretions
alkaline mucus, cholecystokinin (CKK), gastric inhibitory peptide (GIP), and secretin
alkaline mucus
-triggered by parasympathetic vagal stimulation
CKK
- cholecystokinin
- triggered by proteins and fat in chyme
- constricts pyloric sphincter which inhibits gastric emptying (which makes you feel fuller)
- stimulates pancreatic enzyme secretion, increases bile synthesis in liver, and stimulates gallbladder contractions to release bile
GIP
- gastric inhibitory peptide
- triggered by carbs in chyme
- stimulates release of insulin from pancreas
- promotes growth and survival of beta cell
- stimulates adipogenesis (formation of fat cells from stem cells)
secretin
- triggered by decreased pH
- stimulates release of pancreatic buffers (pancreatic amylase and lipase)
- protects duodenum from acidic chyme
- increases mucus secretion in duodenum
- neutralizes pH in duodenum
4 pancreatic enzymes
- pancreatic alpha-amylase: breaks down carbs and starches
- proteases: breaks down proteins to amino acids
- pancreatic lipase: breaks down lipids to fatty acids
- nucleases: breaks down RNA or DNA
3 parts of the small intestine and functions
- duodenum (secretions and hormones to further aid in digestion of chyme)
- jejunum (chemical digestion and nutrient absorption)
- ileum (absorbs bile acids, fluid, and vit B-12)
mesentary
a membrane that attaches the intestine to the abdominal wall and holds it in place
-highly vascularized and depot for fat
large intestine/colon
- final absorption: water, vitamins and electrolytes from chyme
- comes after small intestine; forms and propels feces towards rectum for elimination
- colonic bacteria produce vit K and biotin, help to digest fiber and breast milk, help immune system and brain health
dysfunctions of large intestine
diarrhea, constipation, hemorrhoids (swollen veins in rectum and anus), and diverticulosis (pockets develop in large intestine cause of weakness of muscle walls)
