4 Tubular function 5

Question 1

Answer 1

Question 2

Answer 2

Question 3

what/ where is the major determinant of K+ secretion

Answer 3

its secretion into the lumen in the principal cells of the cortical collecting duct and outer medullary collecting duct.

Question 4

Factors affecting renal K⁺ secretion

Answer 4

Aldosterone and plasma [K⁺] - major determinants of K⁺ secretion.

Flow rate and Na⁺ reabsorption by distal tubule are permissive

1. Aldosterone
   
   • increases Na⁺ reabsorption (­no. & activity of Na⁺ channels -> increases electronegativity of tubule lumen)

• increases Na⁺/K⁺ ATPase activity -> increases cell K⁺
• increases luminal K⁺ permeability (opens K⁺ channels)

2. Plasma [K⁺] -> increases luminal K⁺ permeability

→ increases Na⁺/K⁺ ATPase activity

→ stimulates secretion of aldosterone

3. Distal flow rate K⁺ ‘washout’ (supplies K⁺ - free fluid from proximal sites); washout keeps luminal K⁺ low and allows K⁺ secretion

4. Na⁺ reabsorption without Cl^- -> enhances luminal –vity - promotes K⁺ secretion; & Na⁺ reabsorption stimulates Na⁺/K⁺ ATPase activity

5. Acid-base balance: acidosis – hyperkalemia; alkalosis - hypokalemia

Acidosis: a) ↓ sodium pump

b) ↓ apical membrane permeability to K+
c) increase ­H⁺K⁺ATPase

Question 5

K+ secretion affect on flow rate

Answer 5

increased K+ secretion in principle cells leads to increase flow rate

Question 6

K+ secretion affect on Na+ reabsorption

Answer 6

increased secretion, increased na+ reabsorption

Question 7

Answer 7