Salt & Water transport

Question 1

What does hydrostatic pressure do

Answer 1

Causes water and solute movement into blood vessels

Question 2

Enterocytes on SI villi

Answer 2

Are absorptive and dominate nutrient transport

Question 3

Enterocytes in the crypts

Answer 3

Are secretory with minimal nutrient transport

Water and electrolyte transport in SI and LI is via crypt enterocytes

Question 4

Aldosterone

Answer 4

Upregulates Na absorption by stimulation of Na+/K= ATPase pump and Na channels

Question 5

Glucocorticoids and somatostatin

Answer 5

Increase water and NaCl absorption by up regulation of Na+/K+ ATPase pump

Question 6

Secretion of water and NaCl

Answer 6

Driven by Cl- via crypt enterocytes
Na/K ATPase pumps establish electrochemical gradient across basolateral membrane
This drives Na+, Cl-, K+ through NKCC cotransporters into crypt cells
Cl- leave via apical Cl- channels (eg CFTR) into intestinal lumen- draws Na+ in and water follows into gut lumen

Question 7

How does water get into gut lumen

Answer 7

Hypertonic chyme draws water in
Solutes are absorbed in SI and water follows by osmosis - maintaining the isotonic chyme
Factors that disrupt tonicity or increase enterocyte secretion may cause diarrhoea

Question 8

Cystic Fibrosis

Answer 8

Autosomal recessive
Deletion in gene for CFTR
CFTR is main Cl- channel in apical membrane of gut, pancreatic and airway epithelium
High viscosity of luminal contents - intestinal obstruction (and meconium ileus in newborns)