Digestive Physiology Flashcards
What are the intermediate steps and final steps of carbohydrate catabolism?
intermediate: polysaccharides —amylase—> oligosaccharides/disaccharides
final: disaccharides to monosaccharides
sucrose — sucrase—>glucose + fructose
maltose — maltase —> glucose + glucose
lactose —lactase—> glucose + galactose
What are the intermediate and final steps of protein catabolism?
polypeptides —- pepsin, trypsin, chymotrypsin — > smaller/oligopeptides
oligo/dipeptides — Carboxypeptidase, amino peptidase, dipeptridase —> amino acids
Where does the intermediate step of carbohydrate catabolism typically occur? What are the types amylase and where are they synthesized?
mostly occurs in the area of the duodenum that receives pancreatic amylase
- we do not chew food long enough for salivary amylase to have a greater effect than pancreatic amylase
salivary amylase - produced by salivary glands, released to mouth
pancreatic amylase - produced by pancreas, released to duodenum
Where foes the final step of carbohydrate metabolism occur?
wall of the small intestine in the microvilli
- can be transported across the wall of small intestine
Where does the intermediate step of protein synthesis occur?
pepsin - stomach HCl activates pepsinogen to pepsin
trypsin and chymotrypsin - work in small intestine
polypeptides to oligo/dipeptides
Where dose the final steps of protein synthesis occur?
occurs in the brush border of the small intestine
What kind of digestion and absorption occurs in the mouth?
no absorption, no protein digestion
salivary amylase for carbohydrate digestion
lingual lipase - active at pH 5-6
- remains alive in stomach and small intestine
- does not require bile acids
- minimal absorption
What kind of digestion and absorption occurs in the stomach?
carbs
- no gastric enzyme, denatures salivary enzyme
- no absorption
proteins
- pepsinogen - activated by HCl into pepsin
- polypeptides - dipeptides
- no absorption
lipid
- gastric lipase
- does not require bile salts
- minimal absorption - absorbs alcohol and drugs
MAIN F(x) IS MECHANICAL DIGESTION
What digestion and absorption occurs in the small intestine?
Carbs
- digestion via pancreatic amylase, maltase, lactase and sucrase
protein digestion
- trypsinogen to trypsin
- chymotrypsin
- carboxypeptidase, amino peptidase, dipeptidase
lipid digestion - pancreatic lipase
What stimulates gastric activity?
distension - activates vagus nerve
cephalic - smelling/having food in mouth activates vagus
- preganglionic fibers activate stomach to increase pepsin, HCl, peristalsis
gastrin - G cells release gastrin - goes into blood and back to stomach to increase secretion of HCl, digestive enzymes and muscle motions
low acidity (high pH)
enterogastrin
What inhibits gastric emptying?
sympathetic innervation - thoracic splanchnic nerves
- fight or flight, not rest/digest
- decrease muscles motility, HCl, and enzymes
secretin - from duodenum - inhibitory on stomach
cholecystokinin - from duodenum - inhibitory on stomach
gastric inhibiting peptide - from duodenum - inhibitory on stomach
stretching of the duodenal wall - chyme needs to be neutralized slowly
Describe what effects these hormones that the duodenum release cause: gastric inhibitory peptide, cholecystokinin, secretin
gastric inhibitory peptide - inhibitory on stomach
cholecystokinin - inhibitory on stomach
- excitatory on pancreas - increase digestive enzymes: trypsin, chymotrypsin, pancreatic lipase and amylase
- excitatory on gall bladder - causes it to contract and sends bile salts to duodenum
secretin - inhibitory on stomach
- excitatory on pancreas - releases HCO3-
- excitatory on liver - increases biosynthesis of bile salts and increases bile salts in small intestine
How is salt and water absorbed in the small intestine?
Na active transport by Na/K ATPase pumps at basolateral borders
Cl- passively follows
Water osmotically follows
How are carbohydrates absorbed in the small intestine?
glucose and galactose enter via secondary transport with Na ions
fructose enters via facilitated diffusion
monosaccharides leave basal layer by facilitated diffusion
How are proteins absorbed in the small intestine>?
AA - secondary transport with Na into the cell
amino acids leave by facilitated diffusion
How are lipids absorbed in the small intestine?
formation of micelles which re lipid soluble and diffuse across PM
formation of chylomicrons within the epithelial cells
exocytosis across basolateal membrane into lacteals
how are vitamins absorbed in the small intestine
fat-soluble vitamins (ADEK) absorbed in chylomicrons
water soluble vitamins absorbed by diffusion
give the summary of protein digestion
mouth - no digestion
stomach:
- pepsin hydrolyzes certain peptide bonds - proteins broken into smaller polypeptides
Small intestine
- trypsin and chymotrypsin (from pancreas) hydrolyze other peptide bonds - break them into smaller oligopeptide
- carboxypeptidase removes 1 AA at at time form the carboxyl end of oligopeptide
- occurs mostly in jejunum - some in ileum
BRUSH BORDER (microvilli) OF SMALL INTESTINE
- carboxypeptidase present
- amino peptidase removes one AA at a time from the amino end
- dipeptide splits dipeptide into separate AA
Give the summary of fat digestion and absorption
emulsification - lumen of duodenum
- fat globule broken up by lecithin and bile salts
fat hydrolysis - lumen of SI
- pancreatic lipase act on emulsified droplet
- hydrolyzes 1st and 3rd FA from triglyceride, mono with middle
micelle formation - lumen of SI
- lipids form micelles coated with bile acids
chylomicron formation - intestinal epithelial cells
- ribosomes make proteins for transport in blood
- proteins coat lipid components to form chylomicrons
- exit via exocytosis into lacteal - to heart
Describe what occurs in the large intestine. What is its pH?
secretion - HCO3- and mucus
absorption - mostly occurs in jejunum, some ileum
- active absorption of sodium
- Cl- follows passively down its gradient
- H2O absorbed osmotically
- Vitamin K from E. coli
