Block 2 Lecture 27

Question 1

why does cystic fibrosis result in high salt concentrations in sweat

Answer 1

• as fluid flows into the gland in runs along the reabsorptive sweat duct where Na and Cl are absorbed
• because apical membranes dont have aquaporins the solution becomes hypoosmotic
• Cl- cannot be absorbed in duct cells because CFTR channel is not working so Na+ can’t be reabsorbed either
• because Cl- can’t enter the cell it becomes positive so Na+ can’t come in through their channels

Question 2

what happens when CFTR fails to regulate ENaC due to CF

Answer 2

results in an increase in apical Na+ entry and increase in basolateral Na+ efflux. this makes the blood positive and the Na+ flux is then matched by paracellular Cl- flux. then osmotically obligated eater follows the salt so then the apical airway side in the lungs gets dried out providing a great place for bacteria to colonize