Lecture 58 "Intestine I: Fluid & Electrolyte Transport"
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- villi are composed of
- absorptive cells (enterocytes)
- secretion of mucous by goblet cells is stimulated by
- ACh
- stem cells are located in the
- base of the crypt
- undifferentiated cells of the crypt secrete
- NaCl (and water follows)
-
jejunal enterocytes absorb
ileal enterocytes absorb -
NaHCO3
NaCl -
Transcellular vs. Paracellular Pathway:
*passive diffusion
*bulk flow
*electrodiffusion
*carrier-mediated transport
*active transport -
*passive diffusion: both (diffusion into the lumen is mostly via paracellular pathway)
*bulk flow: paracellular
*electrodiffusion: paracellular
*carrier-mediated transport: transcellular
*active transport: transcellular - solutes and nutrients absorbed by the jejunum (5)
-
monosaccharides
proteins
fats
water-solube vitamins
fat-soluble vitamins - solutes and nutrients absorbed by the distal ileum (2)
-
vitamin B12 (complexed with intrinsic factor)
bile salts -
ability to adapt
ileum can take over for jejunm?
jejunum can take over for ileum? -
ileum can take over for jejunm? Yes
jejunum can take over for ileum? No - jejunal enterocyte absorbs (4)
-
Na (Na/H exchanger or Na/glucose co-transporter)
HCO3 (HCO3/Cl exchanger)
glucose (Na/glucose co-transporter)
amino acids (Na/amino acid co-transporter) - ways in which Na enters the apical membrane of the jejunal enterocyte (2)
-
Na/glucose or Na/amino acid co-transporter
Na/H exchanger - Na leaves the jejunal enterocyte via
- Na/K ATPase pump (located at the basolateral membrane)
-
membrane potential on the serosal side of the jejunal enterocyte:
*before a meal
*after a meal -
*before a meal: +5 mV
*after a meal: +15 mV (due to electrogenicity of Na/K ATPase pump) - ileal enterocyte absorbs (1)
- NaCl
- way in which NaCl enters the ileal enterocyte
-
Na/H exchanger (apical membrane)
HCO3/Cl exchanger (apical membrane) - NaCl absorption by the ileum is inhibited by
- increased levels of cAMP
- cAMP production is stimulated by (4)
-
ACh
VIP (when vipomas are present)
E.coli
Vibriocholera toxin - inhibition of NaCl absorption leads to
- diarrhea (water follows NaCl into ileal lumen)
-
NaCl enters the lumen of the jejunum, ileum, and colon via:
*cell type
*transporters (2) -
crypt cells
CFTR Cl channel (apical membrane)
Na/K/2Cl sympoter (basolateral membrane) - conductane of the CFTR Cl channel is increased by
- increasing levels of cAMP
- conductane of K channel is increased by
- increased intracellular Ca (due to ACh)
- endogenous secretory stimuli (8)
-
ACh
histamine
CCK
secretin
gastrin
GIP
motilin
VIP - exogenous secretory stimuli (6)
-
Vibriocholera toxin
E.coli
Salmonella
bile salts
fatty acids
laxatives - endogenous absorptive stimuli (5)
-
alpha adrenergic agonists (Epi, NE)
dopamine
enkephalins
somatostatin
glucocorticoids - exogenous absorptive stimuli (1)
- nutrients (glucose, amino acids)
- transferrin carries Fe++ to (2)
-
bone marrow
liver - jejunal enterocytes absorb Ca via
- Ca+CaBP ATPase
- Ca ATPase is activated by
- calmodulin
- calcium binding protein (CABP) synthesis in the intestine is stimulated by
- 1,25(OH)2D3 (vitamin D3)
- vitamin D synthesis pathway
- 7-dehydrocholesterol (skin) + UV light --> vitamin D3/cholecalciferol (liver) --> 25(OH)D3 (kidney) --> 1,25-dihydroxycholecalciferol (1,25(OH)2D3)
- increased plasma [Ca] results in (4)
-
decreased secretion of PTH
inhibition of 1,25(OH)2D3 formation
decreased synthesis of CABP
decreased absorption of Ca