Small Intestine Digestion and Absorption of Carbs and Proteins

Question 1

SI or LI for K+ secretion

Answer 1

only large intestine

Question 2

glucose-dependent insulinotropic peptide (GLIP or GIP)

Answer 2

secreted in duodenum and jejunum

only hormone to be stimulated to be secreted by all types of nutrients

results: stimulates beta cells to secrete insulin

inhibits gastric acid secretion

Question 3

glycosidic bonds

Answer 3

bind monosaccharides together

Question 4

starch

Answer 4

mixture of straight and branched chain polymers of glucose

amylose = straight chain
amylopectin = branched
glycogen = branched animal starch

Question 5

sucrose

Answer 5

glucose + frucose

Question 6

lactose

Answer 6

glucose + galactose

Question 7

small intestine can only absorb what size carbohydrate

Answer 7

monosaccharide

**colon cannot absorb any carbs

Question 8

insoluble vs soluble fibers

Answer 8

insoluble fibers = cannot be digested by human enzymes and are excreted unaltered in feces

soluble = partially degraded by enzymes from colonic bacteria

Question 9

first phase of starch digestion

Answer 9

initiated in the mouth by salivary amylase…but bulk is by pancreatic amylase in duodenum lumen

both enzymes = alpha1,4 bonds (amylose and amylopectin)

NOT external bonds nor alpha1,6 bonds that form branch points in the amylopectin molecule

thus digestion by amylase is incomplete and results in oligosaccharides (maltose, maltotriose, alpha-limit dextrins)

Question 10

second phase of starch digestion

Answer 10

brush border in SI

glucoamylase, sucrase, isomaltase –> digest straight chain oligomers into monomers of glucose –> absorbed

isomaltase –> digest alpha-limit dextrins (alpha1,6 bonds)

Question 11

Na+/Glucose transporter 1 (SGLT1)

Answer 11

apical membrane that transports glucose (and galactose) into enterocyte against gradient by coupling it with Na+ transport

Question 12

after SGLT1…fate of glucose and galactose

Answer 12

can be retained for cell’s metabolic needs…

or can exit the cell across the basolateral pole via GLUT2

Question 13

GLUT2

Answer 13

basolateral glucose and galactose transporter out of enterocyte and into ECF

Question 14

GLUT5

Answer 14

apical transporter of fructose into enterocyte

inefficient since not coupled with Na+ uptake like the SGLT1

Question 15

non absorbed starch fate (6-10%) - those that make it out of the SI

Answer 15

metabolized by colonic bacteria into acetate, propionate, and butyrate that are absorbed by the colonic cells

Question 16

gastric peptidase

Answer 16

pepsinogen –> pepsin (acidic pH)

digest 15% of dietary protein

Question 17

pancreatic peptidases

Answer 17

trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A and B

activated by trypsin, which is activated by enterokinase (from jejunum) and trypsin itself

Question 18

trypsin, chymotrypsin, and elastase

Answer 18

endopeptidases with affinity for peptide bonds adjacent to specific amino acids

break down to oligopeptides (2-6 aa)

Question 19

carboxypeptidase A and B

Answer 19

exopeptidases

hydrolyze peptide bonds adjacent to the carboxy terminus

break down to individual amino acids

Question 20

brush border peptidases

Answer 20

peptides –> oligopeptides and amino acids for absorption

Question 21

cytosolic peptidases

Answer 21

oligopeptides –> amino acids

Question 22

amino acid and small peptide transporters

Answer 22

mode of absorption of amino acids, dipeptides, and triepetides in SI

Question 23

absorption of oligopeptides

Answer 23

H+/oligopeptide cotransporter (PepT1)

di –> tetra-peptides

peptidases in the cytoplasm then digest them down to amino acids

Question 24

peptidomimetic drugs

Answer 24

uptake by PepT1

antibiotics and cancer drugs

Question 25

how do amino acids exit the basolateral enterocyte

Answer 25

Na+ - INDEPENDENT transporters (carrier mediated facilitated diffusion)

Question 26

how to amino acids enter the basolateral enterocyte

Answer 26

Na+ - DEPENDENT transporters fueled by Na+ gradient

Question 27

amino acid transport at the enterocyte basolateral membrane

Answer 27

bidirectional uptake of amino acids from the blood is important for cell nutrition and protein synthesis....especially in the crypts where no uptake apical of amino acids is done

Question 28

amino acids entry in apical enterocyte

Answer 28

Na dependent AND independent transporters

Question 29

Na+ dependent amino acid transporters in the apical membrane of the villous cell

Answer 29

B0,+ --> netural and basic amino acids, cystine B0 --> neutral aa X --> acidic aa IMINO --> imino acids (proline, hydroxyproline)

Question 30

Na + independent amino acid transporters in the apical membrane of the villous cell

Answer 30

b0,+ --> neutral and basic, cysteine y+ --> basic aa

Question 31

Na+ dependent amino acid transporters in the basolateral membrane of the villous cell

Answer 31

Lambda --> neutral aa, imino acids ASC --> small neutral, (ala, Ser, Cys)

Question 32

Na+ independent amino acid transporters in the basolateral membrane of the villous cell ***out of cell and into the blood

Answer 32

asc --> small neutral, (ala, Ser, Cys) y+ --> basic aa L --> larger and hydrophobic neutral aminos