L23: Mucosal Digestion

Question 1

digestion breaks down complex nutrient molecules while absorption refers to the transport of simple molecules across the _______

Answer 1

intestinal epithelium

Question 2

much of enzymatic digestion and all of the absorption takes place on?

Answer 2

the surface of intestinal epithelial cells

Question 3

surface extension of the small intestine occurs at what 4 levels

Answer 3

• GI tract elongation
• plica circulares (mucosal folds)
• villi (epithelial projections)
• brush border (Microvilli on surface of villi)

Question 4

what is the glycocalyx

Answer 4

apical membrane covered with glycoproteins of enterocytes

Question 5

what is the mucosal barrier between the lumen and aprical membrane composed of

Answer 5

• microvilli/glycocalyx
• mucus
• water

Question 6

what are the two phases of carbohydrate digestion

Answer 6

• luminal phase - enzymes from salivary glands and pancreas breakdown large polymeric molecules
• membranous phase - “brush border digestion” small polymers are broken down into monomeric molecules that can be asborbed. Enzymes are bound to the epithelium, are part of the glycocalyx

Question 7

what is enteritis

Answer 7

distruction of the epithelial lining; villi are destroyed

Question 8

what enzyme is in the oral cavity and hydrolyzes starch to smaller polysaccharides

Answer 8

alpha amylase

Question 9

in the stomach, ___-___% of starches are converted to maltose

Answer 9

30-40

Question 10

what are the forms of carbohydrates

Answer 10

• fiber (indigestible by mammals)
• sugars
• starches
• glycogen

Question 11

bacterial hydrolases in the rumen/cecum/colon ferment fiber into __?

Answer 11

VFAs

Question 12

T/F: fiber cannot be degraded by luminal or mucosal hydrolases in the small intestine

Answer 12

T

Question 13

T/F: fiber remains in the lumen and provides bulk to the feces; helps in fluid retention and aids in passage

Answer 13

T

Question 14

during the luminal phase of protein digestion, proteins are broken down into ?

Answer 14

peptides & amino acids

Question 15

where does protein luminal phase digestion occur and via what enzymes

Answer 15

begins in stomach w/ gastric enzymes and HCl, is completed in duodenum by pancreatic enzymes

Question 16

what is the membranous phase of protein digestion and whay enzymes are involved

Answer 16

further breakdown of amino acids
peptidases in the apical membrane of enterocytes

Question 17

in protein digestion, luminal and membrane bound ______ facilitate the breakdown to di and tripeptides and amino acids

Answer 17

peptidases

Question 18

what occurs during lipid digestion

Answer 18

triglycerides are hydrolyzed into monoglycerides and FFAs

Question 19

what lipids can be found in the diet

Answer 19

• triglycerides (FAs, glycerol)
• cholesterol
• phospholipids
• lipid soluble vitamins A, D, E, K

Question 20

fats are generally not water soluble whereas ______ enzymes are

Answer 20

lipolytic

Question 21

primary vs secondary bile acids

Answer 21

primary bile acids (Cholic and chenodeozycholic acid) are synthesized by theliver

secondary bile acids are the result of bacterial actions in the colon

Question 22

some bile acids are conjugated with _____ or _____ in the liver

Answer 22

taurine or glycine

Question 23

what are micelles

Answer 23

small sized droplets containing FFA and bile acid
- act as lipid ‘shuttles’ and increase lipid solubility in chyme

Question 24

what are the 4 steps of fat digestion in the SI

Answer 24

1. emulsification by bile salts
2. hydrolysis of triglycerides
3. micelle formation
4. micelle content absorbed in jejunum

Question 25

carbohydrate digestion ends with … in the membranous phase

Answer 25

monomers (glucode, fructose, galactose)

Question 26

protein digestion ends with…

Answer 26

di and tripeptides and amino acids

Question 27

where is enterokinase located and what does it do

Answer 27

in the brush border, activates trypsin from trypsinogen

Question 28

what enzyme is responsible for the inital minimal digestion of fat digestion in the oral cavity

Answer 28

lipase

Question 29

where does fat emulsification occur

Answer 29

stomach and small intestine

Question 30

the initial emulsification of fat in the stomach occurs with HCl, whereas the finalization of emulsification in the small intestine uses…

Answer 30

bile acids + phospholipids

Question 31

insufficient synthesis and secretion of enzymes from 90% of pancreas

Answer 31

Exocrine pancreas insufficiency (EPI)

Answer 32

produced by epithelial cells in the glycocalyx in duodenum