Crr Week 3: Regulation Of K, Ca, And Mg (Benjayati)

Front 1

Filtered K+ is mostly reabsorbed in which portion of the nephron?

Back 1

90% reabsorbed in the proximal tubule and loop of Henle
(obligate reabsorption)

Front 2

Which cells reabsorb K+ and which cells secrete K+ in the distal tubule and collecting ducts?

Back 2

Intercalated cells --> reabsorb K+
Principle cells --> secrete K+

Front 3

What is the most important regulatory site for K+?

Back 3

Distal nephron
(distal tubule and collecting ducts)

Front 4

Aldosterone stimulates secretion in which portion of the nephron?

Back 4

Cortical collecting duct

Front 5

How is K+ secreted by cortical collecting duct cells? Is this an active or passive process?

Back 5

K+ diffuses passively across K+-channels into the lumen
(This is accomplished due to the build up of K+ from the Na+-K+-ATPase. The high intracellular concentration of K+ allows K+ to diffuse into the collecting duct)

Front 6

List 5 major factors that favor K+ secretion in the cortical collecting ducts.

Back 6

1. Steeper concentration gradient for K+ (higher plasma K+ concentration)
2. Acid-base balance (alkalosis)
3. Na+ concentration of tubular fluid (more Na+ reabsorbed, more negative lumen potential)
4. Flow rate of tubular fluid
5. ALDOSTERONE

Front 7

How does an increased flow rate increase K+ secretion?

Back 7

Increased flow rate reduces luminal K+ concentration, creating better diffusion gradient for K+.

Front 8

What is the action of furosemide?

Back 8

Loop diuretic
*Inhibits Na-K-2Cl-cotransport in the thick ascending loop of Henle, destroying the positive luminal potential

Front 9

What is the action of thiazide diuretics?

Back 9

Inhibits Na-Cl-cotransport in early distal tubule

Front 10

What is the action of the diuretic, amiloride?

Back 10

Blocks Na+ channels in the distal nephron
(destroys negative luminal potential that is necessary for K+ secretion)

Front 11

Which diuretic will not promote K+-secretion and why?

Back 11

Amiloride
(Blocks Na+ channels in the distal nephron. This makes the lumen more positive, so K+ secretion is not promoted)

Front 12

How does aldosterone stimulate K+ secretion and where does this take place?

Back 12

1. Stimulates Na+-K+-ATPase which increases the concentration gradient of K+
2. Increases the number of K+ channels
3. Makes the lumen more negative by stimulating the reabsorption of Na+

Front 13

Which disease results from absent aldosterone, and which disease results from too much aldosterone?

Back 13

Addison's disease (no aldosterone, high K+ plasma)

Primary aldosteronism (high aldosterone, low K+ plasma)

Front 14

Extracellular calcium concentration is regulated by which 3 organs?

Back 14

1. Bone
2. Intestines
3. Kidneys

Front 15

How much Ca2+ is filtered, and where does most of the reabsorption take place?

Back 15

99% is filtered (like Na+)
Reabsorption occurs in the proximal tubule

Front 16

How is Ca2+ reabsorbed in the proximal tubule (active or passive transport)?

Back 16

Paracellular (passive diffusion) pathway

Front 17

How is Ca2+ reabsorbed in the distal tubule (active or passive transport)?

Back 17

Transcellular (active) pathway involving:
1. Ca2+ channel on luminal membrane (stimulated by PTH)
2. Na-Ca-exchanger or Ca-ATPase on peritubular membrane

Front 18

What is the major regulatory site for Ca2+ reabsorption in the nephron?

Back 18

Distal convoluted tubule
(Where PTH and vitamin D directly stimulate its reabsorption when plasma Ca2+ is low)

Front 19

What is the effect of Calcitonin on renal handling of Ca2+?

Back 19

No effect

Front 20

Where is the major site of Mg2+ reabsorption in the nephron?

Is Mg2+ reabsorbed paracellularly or transcellularly?

Back 20

Thick ascending loop of Henle

*Transported paracellulary
(driven by the (+) luminal PD and facilitated by the junctional complex protein, paracellin)

Front 21

What protein facilitates the transport of Mg2+?

Back 21

Paracellin

Front 22

At which portion of the nephron is Na+ and Ca2+ reabsorption dissociated?

Back 22

Distal tubule

Front 23

Is Ca2+ reabsorption affected by loop diuretics?

Back 23

YES.
Loop diuretics disrupt the lumen-positive potential gradient by inhibiting the Na+-K+-2Cl-cotransporter. Without the repellent (+) charge across the lumen, Ca2+ does not diffuse paracellularly as it should.

*Loop diuretics can be used for treatment of hypercalcemia

Front 24

Do loop diuretics affect Mg2+ reabsorption?

Back 24

YES
Loop diuretics disturb the positive lumen potential difference, so Mg2+ is no longer repelled across the luminal membrane.

Front 25

Which part of the nephron is responsible for adjustments in K+ excretion that occur when dietary K+ varies?

Back 25

Distal tubule and collecting ducts

Front 26

What factor determines the magnitude of K+ secretion?

Back 26

Size of the electrochemical gradient for K+ across the luminal membrane

Front 27

How do loop and thiazide diuretics affect K+ secretion?

Back 27

Increase K+ secretion
(They inhibit Na+ reabsorption "upstream" to the principle cells, causing increased Na+ delivery to the principle cells. This allows more K+ to enter the cell via Na+-K+-ATPase).

Front 28

Does acidosis or alkalosis increase K+ secretion?

Back 28

Alkalosis
(Decreased H+ concentration inhibits action of H+ and K+ exchange across the basolateral membrane. If there is low H+ concentration, H+ leaves the cell to aid in buffering and K+ enters the cell. A higher K+ intracellular concentration creates a strong driving force for secretion).

Front 29

Why do diuretics acting on sites "upstream" to the K+ secretory site promote K+ secretion?

Back 29

K+ secretion is promoted in two ways by these diuretics:
1. Increased tubular flow dilutes the tubular concentration of K+, creating a bigger concentration gradient for K+ secretion
2. Increase delivery of Na+ to the distal tubule. More Na+ reabsorption = more K+ secretion due to the (Na+-K+-ATPases)