Epithelial transport

Question 1

Two categories of epithelia

Answer 1

Secretory and absorptive

Question 2

Common features

Answer 2

Sheets of cells
Separated by lateral intercellular spaces
Held by tight junctions
Able to transport ions from one side to another
Asymmetry of structure and function

Question 3

Function of leaky epithelia

Answer 3

Bulk transport of iso-osmotic solutions
Found proximally
Paracellular pathway for ions and water
Carrier mediated transport on apical membrane with Na+

Question 4

Function of tight epithelia

Answer 4

Withstand large osmotic gradients 
More regulated transport 
Only transcellular 
Low water permeability 
Na+ channels on apical, inhibited by amiloride and regulated by aldosterone

Question 5

Absorptive epithelia properties

Answer 5

Na+/K+ ATPase on the basolateral create an inward sodium gradient
K+ recycling
Na+ gradient from lumen
Vectorial transport of sodium and associated solutes

Question 6

Secretory epithelia properties

Answer 6

Active Cl- transport, but still dependent on Na+ ATPase
Basolateral has NK2CC
Cl- exit on apical into lumen
Na+ move through paracellular, K+ recycle

Question 7

overall functions of kidney

Answer 7

regulatory
excretory
endocrine (erythropoietin, vit D activation)