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9.5 - GI PHYSIOLOGY > Intestinal absorption > Flashcards

Intestinal absorption Flashcards

1
Q

Epithelia types in sections

A

Small intestine = leaky, paracellular occurs

Large = tight epithelium, transcellular so more highly regulated

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2
Q

Water reabsorption mechanism

A

Osmosis secondary to solute reabsorption
Na+ movement underlying
Through tight junctions and aquaporins

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3
Q

Types of transporter

A

Passive diffusion = ENaC
Na/H exchanger = NHE
Na+ coupled exchanger
Na/K ATPase

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4
Q

Aldosterone action

A

Increases Na+ absorption

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5
Q

Absorption in small intestine (start)

A

Coupled transport of amino acids and glucose with Na+

NHE on apical creates gradient for Na+ to move into cell, also creates gradient for Cl- to be reabsorbed paracellularly

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6
Q

Absorption in later small intestine

A

HCO3- into lumen and Cl- into cell exchanger
Cl- into cell
Cl- leaves on basolateral with K+ (KCCl)
NHE operates in parallel with an anion exchanger
CO2 hydration occurring in cell with carbonic hydrate

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7
Q

Colon and rectum

A

Cl- accumulated using the gradient of HCO3- from CA reaction
Apical Na+ influx through ENaC
Cl- efflux on basolateral
NHE on basolateral removes H+
- Na+ less important, paracellular less important

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8
Q

Potassium absorption/ secretion

A

Can be absorption or secretion
Passive absorption paracellular in small intestine,
Active absorption with H/K ATPase in colon, then K-Cl symporter on basolateral takes K+ into interstitium
Can have active secretion in colon, through action of Na-K ATPase and diffuse across apical
can have passive secretion through paracellular

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9
Q

Calcium absorption

A

Occurs in upper duodenum, against a transepithelial gradient
Calcium enters through specific channels (ECaC), binds to protein in cytosol (calbindin) and exits on basolateral via a ATPase

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10
Q

Iron absorption

A

Apical membrane divalent cation transporter, with copper and zinc as well
Becomes Fe3+ in cell
Can be stored or in the blood bound to ferritin

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11
Q

Types of uptake of nutrients

A
  • Hydrolysis in lumen and then uptake (proteins)
  • Hydrolysis on the apical membrane (disaccharides)
  • Absorption into and hydrolysis within cell (di/tri peptides)
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12
Q

Carbohydrate breakdown

A

Salivary and pancreatic amylases

Brush border enzymes hydrolyse these products to give glucose, fructose, galactose

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13
Q

Carbohydrate absorption

A

D-Glucose and D-galactose absorbed on apical SGLT1
Monosaccharides exit basolateral on glut2 (hexoses)
Occurs by midi-jejunum

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14
Q

Protein breakdown

A

Pepsinogen -> pepsin in the stomach
Further digestion at brush border can occur
Pepsin, trypsin, chymotripsin
Enterokinase activates intestinal peptidases

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15
Q

Protein absorption

A

Amino acids are absorbed by apical carriers, Na+ dependent
Di/tri peptides can be directly absorbed by H+ dependent apical carrier proteins, then broken down inside cell
By the end of the jejunum
Exit cell on basolateral by Na+ independent carrier

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16
Q

Lipid breakdown

A

Muscular movements of the stomach emulsify fats, aided by lingual lipases
Most digestion in small intestine
Pancreatic lipase digest triglycerides -> monoglycerides and free FA
Products incorporated into bile salt micelles

17
Q

Lipid absorption

A

Micelles diffuse to unstirred acidic layer adjacent to apical membrane, components dissociate at cell surface
Components are reassembled in the SER, form microscopic chylomicron particles
Chylomicrons exported to Golgi and pass into lymph
Lymph -> left subclavian vein via thoracic duct

18
Q

Water soluble vitamin absorption

A

B1, B2, B12

Passive diffusion, specific Na+ coupled carrier proteins

19
Q

Lipid soluble vitamin absorption

A

Steroids, vitamin A,D,E,K

Absorbed in bile micelles, mostly exit the epithelial cell unmodified in chylomicrons

20
Q

where does protein breakdown begin

A

acidic stomach

21
Q

enzymes in protein breakdown

A 
pepsin = from stomach
pancreatic peptidases (trypsin/chymotrypsin/elastase/carboxypeptidases) responsible for the bulk of digestion of proteins to oligopeptides and aa
22
Q

where does further digestion of oligopeptides to amino acids occur

A

brush border peptidases

23
Q

protein absorption

A

amino acids absorbed by apical carriers, mostly Na+ dependent, different categories of transporters
di and tri peptides directly absorbed by H+ dependent. apical career protein

24
Q

role of intracellular peptidases

A

converts the absorbed di and tri peptides into amino acids in cells

25
Q

absorption of amino acids finished by

A

end of jejunum

26
Q

break down of carbohydrates

A
  • salivary amylase initiates
  • pancreatic amylase renders most starch in the form of disaccharides, trisaccharide and alpha limit dextrin
  • brush border disaccharides release glucose, fructose and galactose
27
Q

active absorption of carbohydrates

A

active absorption of D-glucose and D-galactose across apical membrane by Na+ dependent (SGLT-1)

28
Q

fructose absorption

A

facilitated diffusion GLUT 5

29
Q

exit of hexoses across basolateral

A

via GLUT2

30
Q

oral rehydration solutions

A

given for diarrhoea to provide electrolytes
isosmotic salt/glucose solution (1:1)
contain sodium and potassium

31
Q

what happens to unabsorbed carbohydrates

A

enter the colon as fuel for gut microflora, basically is fermented

32
Q

bicarbonate secretion in duodenum

A

neutralise stomach acid

  • create bicarbonate from hydration of CO2 using CA
  • exchanger with Cl- on apical puts HCO3- into lumen
33
Q

regulation of calcium absorption

A

ECaC and calbindin synthesis regulated by the vitamin D derived hormone calcitriol

34
Q

cell polarity in GI

A 
apical = lumen 
basolateral = interstitium/ blood
35
Q

different methods of macromolecules absorption

A

hydrolysis in lumen followed by absorption (proteins -> aa)
hydrolysis on apical membrane (disaccharides)
absorption into and hydrolysis within cell (di/tri peptides)
- following luminal hydrolysis, substances may be taken top and then resynthesises in the cell, eg. triglycerides

36
Q

disaccharides split into

A

lactose -> glucose and galactose (via lactase)
maltose -> glucose (maltase)
sucrose -> maltose (sucrase)

hydrolysed before absorption in small intestine

37
Q

importance of brush border disaccharidases

A

hydrolyse products of main amylase enzymes and sucrose and lactose to give glucose, fructose, galactose

38
Q

importance of brush border disaccharidases

A

hydrolyse products of main amylase enzymes and sucrose and lactose to give glucose, fructose, galactose

9.5 - GI PHYSIOLOGY (7 decks)

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