K+ and Ca2+ (Muster) - W2

Question 1

where is K+ primarily stored?

What could deplete those stores?

Answer 1

• 98% intracellularly
• burns
• crush injuries
• reperfusion injuries

Question 2

How does insulin affect K+?

Answer 2

• insulin increases Na-K ATPase
• promotes skeletal and muscle uptake
• eat –> insulin –> alleviates K+ serum

Question 3

How do catecholamines affect K+?

Answer 3

• bind to B2 receptors
• stimulate the Na-K ATPase inducing cellular uptake
• likely permissive at baseline

Question 4

How does plasma concentration of K+ affect uptake?

Answer 4

• serum K+ rises –> cellular uptake increased

Question 5

How does exercise affect K+?

Answer 5

• muscle cells release K+
  
  • related to degree of exercise

Question 6

How does pH affect K+

Answer 6

• K+ rises in serum.

Question 7

What happens with tonicity and K+?

Answer 7

• hyperglycemia
  
  • water and K+ leave the cell
  • more water than K+ leaves
• K+ inside cell reduces Na-K ATPase

Question 8

What do you give to prevent arhythmia and cardiac arrest with high potassium?

Answer 8

• Ca2+

along w/insulin and glucose

Question 9

What is the control of potassium:

proximal tubule

thick ascending limb

principle cell of collecting duct

Answer 9

• proximal tubule = 55-65% via tight junctions
• thick ascending limb = 25%
• principle cell = 10%

Question 10

What are the 4 stimuli for K+ secretion (and therefore excretion)

Answer 10

1. sodium delivery to distal convoluted tubule
   
   1. more sodium = more K+ excretion
2. increased flow rates
   
   1. higher flow = higher gradient stimulating movement into the lumen
3. plasma levels of K+
   
   1. increased activity of ATPase w/higher levels
4. aldosterone
   
   1. increases ENAC
   2. increases ROMK
   3. increases NA-K ATPase

Question 11

What 2 things can stimulate aldosterone and what happens with each?

Answer 11

1. Angiotensin II system
   
   1. used for NA+ retention
   2. stops ROMK channel
2. serum potassium
   
   1. ​increases ROMK in membrane
   2. less stimulus for ang II

Question 12

What are the stimuli for BK channel?

Answer 12

1. increased FLOW
2. increased EC potassium

Question 13

How is K+ reabsorbed?

Answer 13

• occurs in Alpha and beta intercalated cell
• K+ is exchanged for H+
  
  • lots of H+ must be processed to reabsorb K+
• active process!!
• also requires reabsorption of bicarbonate

Question 14

Describe the availability of calcium

Answer 14

• 40-50% is bound to ALBUMIN
• 10% BOUND to citrate, phosphate
• 50% is available as ionized calcium

Question 15

How much calicum is aborsbed in each part of the loop?

Answer 15

• proximal tubule = 60-70%
• thick segment = 20%
• convoluted tubule = 10%
• collecting duct = 5%

Question 16

By which process is most of the calcium reabsorbed?

Answer 16

• paracellular (85%)

Question 17

How is calcium reabsorbed in the thick ascending limb?

Answer 17

• calcium sensing receptor
  
  • ​binds free calcium
  • when stuff isn’t bound, upregulates calcium reabsorption
  • bound = claudins can stop paracellular reabsorption of calcium

Question 18

How is calcium reabsorbed in the distal convoluted tubule and cortical collecting duct?

Answer 18

• enters through TRPV5 channels
  
  • most is transcellular
• binds to calbindin to carry it to the other side of the cell.
• Na+/Ca2+ antiporter allows it into the capillary.
  
  • 3Na in to 1Ca out.
• PTH can upregulate TRPV5 for increased uptake on luminal side and increased excretion on back side.

Question 19

When is PTH released?

Answer 19

• PTH is released when all calcium receptors aren’t bound.
• low ionized calcium stimulates PTH release.

Question 20

What does PTH do to bone?

Answer 20

• stimulates IMMEDIATE release of stored skeletal calcium
• LONG TERM
  
  • stimulates bone reabsorption
  • acts on cortical bone
  • also releases phosphorus

Question 21

What does PTH do to the gut?

Answer 21

• increases calcium and phosphate reabsorption by increased 1,25 vitamin D

Question 22

What does PTH do to the kidney?

Answer 22

• increases the production of vitamin D in the proximal tubule
• increases renal Caclium reabsorption
• stimulates renal phosphorus excretion - phosphorus wasting.