6 absorption of ions and water Flashcards
What is the difference between villous and crypt enterocytes?
villous - absorption
Crypt - secretion
What 3 structures increase the surface area of the small intestine?
macroscopic fold of Kerckring
Villi
Microvilli
What are the 2 main routes for water absorption?
transcellular
pararcellular
What are the 4 routes of entry for sodium ions?
Na/(glucose or amino acid) co-transport
Na-H transporter
parallel Na-H and Cl-bicarbonate exchange
epithelial Na channels
what transporter could be used in Na/glucose co-transport, what else facilitates this movement?
SGLT1
Na/K ATPase in basolateral membranes
What facilitates the movement of H ions in the Na-H into the gut lumen?
lumen is full of bicarbonate ions
in parallel Na-H exchange, what secondary messenger inhibits Na uptake?
cAMP, cGMP, and Ca
In the fasting state, what is significant about parallel Na-H and Cl/HCO3 exchange?
it’s electroneutral
What sort of steroid hormone might increase Na absorption?
How?
minerlocorticoids, like aldosterone
increase apical Na channel opening
increase Na channel number
increased synthesis of Na channels and Na-k pumps
What are the 3 routes of entry for Chloride ions?
passive Cl absorption (channels)
Parallel Na-H and Cl-HCO3 exchange
independent Cl-HCO3 exchange
What is congenital chloridorrhoea, how might it present, and how would you treat it?
autosomall recessive, absence of Cl-HCO3 exchanger
dairrhoea, reduced bicarbonate secretion, (alkalyosis)
PPI
Give 4 examples of absorptagogues
angiotensin
aldosterone
somatostatin
noradrenaline
What effect will dehydration have on Na absorption?
stimulates renin-aldosterone axis, increasing Na absopriton using absorptagogues
Name 2 types of bacterial endotoxins?
cholera
E.coli
How does Cholera inhibit Na absorption?
cAMP increase, increasing Cl and K secretion and inhibits NaCl absorption
How woul ACh inhibit absorption?
Gq, Ca
What is Verner Morrison syndrome?
pancreatic tumours ultimately cause cAMP increase and hence extensive diarrhoea
What is Loperamide?
a secretagogue, acting on myenteric plexus in large intestine to decrease motility
What are some examples of natural laxatives?
bile acids
Ca
How can Ca absorption be passive?
not under the control of the VDR
Where is Ca absorbed?
duodenum epithelium
What are the 3 steps in Ca absorption?
Ca channels
Ca binds to calbindin, acting as a buffer
Ca pump and Na-Ca exchanger on basolateral membrane expel Ca into interstitial fluid
