Loop of Henle, Distal tubule and Collecting Duct - Rao

Question 1

Describe the cells of the thin descending limb.

Answer 1

Thin epithelial cells with few mitochondria

Question 2

What is the tonicity of the interstitial environment compared to plasma?

Answer 2

Interstitial environment is hyperosmotic compared to plasma

Question 3

Describe the permeability to water, NaCl, and urea in the thin descending limb.

Answer 3

Water - highly permeable
NaCl - impermeable
Urea - impermeable

Question 4

Describe the permeability to water, NaCl, and urea in the thin ascending limb.

Answer 4

Water - highly impermeable
NaCl - permeable (strong reabsorption 20-25%)
Urea - impermeable

Question 5

Describe the cells of the thick ascending limb.

Answer 5

Thick epithelial cells with many mitochondria

Question 6

What transporters are present in the thick ascending limb?

Answer 6

Na K 2Cl cotransport - apical
Na K ATPase antitransport - basolateral
Cl channel - basolateral
K Cl cotransport - basolateral
K channel - apical (K -> lumen)

Question 7

What can inhibit NaK2Cl transporter?

Answer 7

Diuretic agents with high affinity for Cl site

Furosemide, bumetanide

Question 8

What is the net result of fluid passing through the DCT and CT?

Answer 8

Dilution of tubular fluid (if impermeable to water)

Question 9

How is sodium reabsorbed in the DCT?

Answer 9

Electrically conductive Na channels

Na / Cl cotransporter

Question 10

What diuretics block electrically conductive Na channels?

Answer 10

Amiloride

Triamterene

Question 11

What diuretics inhibit Na / Cl cotransporters?

Answer 11

Thiazide diuretics

Question 12

What is the driving force for potassium secretion in the DCT and CT?

Answer 12

High intracellular concentration of K caused by Na K ATPase

Lumen-negative transepithelial voltage

Question 13

What are regulatory factors affecting K secretion?

Answer 13

Increased flow by diuretics cause increased K secretion

Increased Na reabsorption increases K secretion

Question 14

What is the affect of loop diuretics, thiazides, and amilorides on K secretion?

Answer 14

Loop diuretics - increase K secretion
Thiazides - no change
Amilorides - no change

Question 15

How is Na reabsorbed in the CT?

Answer 15

Electrically conductive Na channels

Question 16

Where is aldosterone synthesized and where does it act?

Answer 16

Synthesized - adrenal cortex

Act - DCT and CT

Question 17

What are aldosterone’s actions?

Answer 17

Increase Na reabsorption

Increase K secretion

Question 18

What is Addison’s disease?

Answer 18

Complete lack of aldosterone

Increased urinary excretion of NaCl

Question 19

What is Conn’s Syndrome?

Answer 19

Aldosterone secreting tumor
Increased Na reabsorption / K secretion
Hypokalemia, hypernatremia, hypertension

Question 20

What factors stimulate aldosterone?

Answer 20

Reduced ECF volume
Reduced plasma Na
Increased plasma K
Increased plasma AT II
Trauma / stress

Question 21

What is reabsorbed and secreted in the DCT and CD to maintain acid-base balance?

Answer 21

Bicarbonate - reabsorbed

Protons - secreted

Question 22

What do principal cells do?

Answer 22

Na - reabsorb

K - secrete

Question 23

What do intercalated cells do?

Answer 23

Proton - secrete

Bicarbonate - secrete (some cells)

Question 24

How are protons secreted in the DCT and CD?

Answer 24

Under acidosis conditions
Proton activated ATPase (luminal; proton pumped to lumen)
H K ATPase (luminal; H to lumen; K to cell)
HCO3 / Cl exchanger (basolateral; HCO3 to ISF; Cl to cell)

Question 25

Under what conditions and how is bicarbonate secreted?

Answer 25

Under alkalosis condition
H ATPase (basolateral; proton to ISF)
HCO3 / Cl exchanger (luminal; HCO3 to lumen)
alpha cell - luminal proton channel
beta cell - luminal bicarbonate channel

Question 26

What sitmulates distal nephron calcium reabsorption?

Answer 26

Parathyroid hormone