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Physiology GI > Small Intestine Digestion and Absorption of Carbs and Proteins > Flashcards

Small Intestine Digestion and Absorption of Carbs and Proteins Flashcards

1
Q

SI or LI for K+ secretion

A

only large intestine

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2
Q

glucose-dependent insulinotropic peptide (GLIP or GIP)

A

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

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3
Q

glycosidic bonds

A

bind monosaccharides together

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4
Q

starch

A

mixture of straight and branched chain polymers of glucose

amylose = straight chain
amylopectin = branched
glycogen = branched animal starch
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5
Q

sucrose

A

glucose + frucose

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6
Q

lactose

A

glucose + galactose

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7
Q

small intestine can only absorb what size carbohydrate

A

monosaccharide

**colon cannot absorb any carbs

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8
Q

insoluble vs soluble fibers

A

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

soluble = partially degraded by enzymes from colonic bacteria

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9
Q

first phase of starch digestion

A

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)

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10
Q

second phase of starch digestion

A

brush border in SI

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

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

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11
Q

Na+/Glucose transporter 1 (SGLT1)

A

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

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12
Q

after SGLT1…fate of glucose and galactose

A

can be retained for cell’s metabolic needs…

or can exit the cell across the basolateral pole via GLUT2

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13
Q

GLUT2

A

basolateral glucose and galactose transporter out of enterocyte and into ECF

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14
Q

GLUT5

A

apical transporter of fructose into enterocyte

inefficient since not coupled with Na+ uptake like the SGLT1

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15
Q

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

A

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

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16
Q

gastric peptidase

A

pepsinogen –> pepsin (acidic pH)

digest 15% of dietary protein

17
Q

pancreatic peptidases

A

trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A and B

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

18
Q

trypsin, chymotrypsin, and elastase

A

endopeptidases with affinity for peptide bonds adjacent to specific amino acids

break down to oligopeptides (2-6 aa)

19
Q

carboxypeptidase A and B

A

exopeptidases

hydrolyze peptide bonds adjacent to the carboxy terminus

break down to individual amino acids

20
Q

brush border peptidases

A

peptides –> oligopeptides and amino acids for absorption

21
Q

cytosolic peptidases

A

oligopeptides –> amino acids

22
Q

amino acid and small peptide transporters

A

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

23
Q

absorption of oligopeptides

A

H+/oligopeptide cotransporter (PepT1)

di –> tetra-peptides

peptidases in the cytoplasm then digest them down to amino acids

24
Q

peptidomimetic drugs

A

uptake by PepT1

antibiotics and cancer drugs

25
Q

how do amino acids exit the basolateral enterocyte

A

Na+ - INDEPENDENT transporters (carrier mediated facilitated diffusion)

26
Q

how to amino acids enter the basolateral enterocyte

A

Na+ - DEPENDENT transporters

fueled by Na+ gradient

27
Q

amino acid transport at the enterocyte basolateral membrane

A

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

28
Q

amino acids entry in apical enterocyte

A

Na dependent AND independent transporters

29
Q

Na+ dependent

amino acid transporters in the apical membrane of the villous cell

A

B0,+ –> netural and basic amino acids, cystine

B0 –> neutral aa

X –> acidic aa

IMINO –> imino acids (proline, hydroxyproline)

30
Q

Na + independent

amino acid transporters in the apical membrane of the villous cell

A

b0,+ –> neutral and basic, cysteine

y+ –> basic aa

31
Q

Na+ dependent

amino acid transporters in the basolateral membrane of the villous cell

A

Lambda –> neutral aa, imino acids

ASC –> small neutral, (ala, Ser, Cys)

32
Q

Na+ independent

amino acid transporters in the basolateral membrane of the villous cell

***out of cell and into the blood

A

asc –> small neutral, (ala, Ser, Cys)

y+ –> basic aa

L –> larger and hydrophobic neutral aminos

Physiology GI (11 decks)

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