Intestinal Fluid and Electrolyte Transport

Question 1

What part of the small intestine is the major site of Na absorption?

Answer 1

Jejunum

Question 2

How does Na enter the enterocytes on the apical side and how does it leave on the basolateral site?

Answer 2

On the luminal side, Na enters via, Na-dependent cotransporters like Na-amino acid cotransorte,r Na/H exchanger, Na-monosacharide cotransporter. On the basolateral side it’s pushed out via Na/K ATPase pump.

Question 3

What’s the difference in types of transporters present in jejunum vs ileum?

Answer 3

Both has Na dependent cotransporters on the apical side, and a Na/K ATPase on the basolateral side. Major difference is that in the ileum, there’s a HCO3-/Cl- exchanger where HCO3 is secreted out to the lumen and Cl is brought into the cell which then is pushed out on the basolateral side to end the blood.
In the jejunum however, there’s no Cl channels, and the HCO3 transporter is located on the basolateral side which brings bicarb back to the blood instead of secreted it out like in the ileum.

Question 4

In the colon, what kind of channels will you find on the apical side?

Answer 4

Na and K channels which secretes K and reabsorb Na.

Question 5

Which part of the GI are you likely to find Na channels that were induced by aldosterone?

Answer 5

Colon

Question 6

Where on the intestinal epithelium are you likely to find Na/K/2Cl cotransporters like the ones seen in the kidney.

Answer 6

On the basolateral membrane of epithelial cell linings of the intestinal crypts.

Question 7

Diarrhea has relatively high concentration of which electrolyte and why?

Answer 7

HCO3-, due to GI tract being high in HCO3 content including salivary, pancreatic and intestinal juices.

Question 8

Are you likely to find high K concentration in diarrheal fluid?

Answer 8

Yes, due to flwo-rate dependent K secretion by the colon

Question 9

How does lactase deficiency cause osmotic diarrhea?

Answer 9

Whithout lactase, lactose cannot be digested and so it stays int he intestinal lumen incresing osmolarity and and water follows omsolarity

Question 10

Name the steps by which Cholera causes secretory diarrhea.

Answer 10

1. cholera toxin enters intestinal cell
2. a toxin subunit detach and binds to the basolateral membrane where it catalzyes ADP ribosylation of the alpha subunit and in of the Gs protein that is coupled to adenyl cylase
3. ADP-ribosylation of the alpha subunit inhibit GTPase activity and so gt P cant convert back to GDP. with GTP permanently bound to the alpha-subunit, adenyly cylase is permanently activated
4. cAMP levels remain high and Cl channel on the apical membrane are kept open