Basic Epithelial Transport Mechanisms

Question 1

Reabsorption (and secretion) involves crossing two barriers, list them.

Answer 1

1. tubule epithelium

2. Endothelial cells lining the peritubular capillaries.

Question 2

What is Fanconi Syndrome?

Answer 2

Disease of proximal tubules, +/- azotemia, PU/PD wt. loss, glucosuria, hyperphosphatemia, hypokalemia, acidosis, aminoaciduria, dilute urine.

Question 3

Describe the two possible ways to cross the epithelial barrier for reabsorption.

Answer 3

1. Paracellular route- (single step) substance goes “around” cells through matrix of tight jxns.
2. Transcellular route- (two steps) more common, cross apical memb facing lumen –> coss basolateral memb.

Question 4

List four ways substances can move across membranes and cells.

Answer 4

1. diffusion
2. Transporters,
3. Channels
4. Active transport

Question 5

Describe movement of ions by transporters.

Answer 5

Many extremely specific, slower than channels, binds stronger, carrier proteins undergo more elaborate conformational change

Question 6

List 3 types of transporters.

Answer 6

1. Uniporters
2. Symporters/Antiporters
3. Primary active transport.

Question 7

Describe the SGLT (sodium glucose linked transporter)

Answer 7

Symporter, move 1 glucose and 1/2 Na molecules

Question 8

Describe the NHE proteins (Na/H exchange)

Answer 8

Antiporters, move Na into cells and H out

Question 9

Describe characteristics of “channels”

Answer 9

rapidly move large amts of substance, specificity is often low, pores can be opened/closed to control flow.