Lecture 19: Regulating Renal Ion [ ]

Question 1

What is normal extracellular [ ] of K+ ion?

Answer 1

Normal= 4.2 mEq/L

Question 2

What is the clinical significance of excess extracellular K+?

Answer 2

Cardiac arrhythmias, cardiac arrest, or fibrillation.

Question 3

Why must the kidneys be able to rapidly adjust extracellular K+ [ ]?

Answer 3

Must be maintained around 4-5 d/t risk of cardiac arrhythmias, arrest, fibrillation.

Must be maintained b/c of the varied intake in a diet to keep balanced. [take in alot in diet vs low [ ] extracellular.

Question 4

What is the overall effect of aldosterone secretion on K+ excretion?

Answer 4

Increase in extracellular K+ stimulates increase in aldosterone secretion= more K+ excretion

Fig 30-4: aldosterone increases = K+ excretion increases

Aldosterone and extracellular [K+] factors in K+ excretion

Question 5

What part of the renal tubule is responsible for K+ reabsorption and what part is responsible for K+ secretion?

Answer 5

Reabsorption: proximal tubule and ascending limb of henle

Secretion: late tubule and collecting duct

Question 6

Describe the mechanism by which principal cells secrete K+?

Answer 6

Na+ is pumped into the interstitial
K+ is pumped out of cell into tubular lumen.

This is stimulated by K+ and aldosterone.

Maybe look up more?

Question 7

What factors stimulate principal cells to secrete k+?

Answer 7

Aldosterone and extracellular [K+] factors in K+ excretion

Question 8

Describe the relationship btw tubular flow rate and K+ secretion:

Answer 8

High K+ diet greatly enhances effect of increases tubular flow rate to increase K+ secretion.

High K+ intake greatly increases the K+ secretion rate even at low tubular flow rates.

Conditions that cause increase tubular flow rate: volume expansion, some diuretics, and high Na+ diet

Question 9

Describe and explain why high Na intake has little effect on K+ excretion.

Answer 9

High Na+ intake decreases aldosterone secretion, which decreases K+ excretion.

Can eliminate Na+ w/o eliminating K+, BUT

This increases GFR and decreases proximal tubular reabsorption of Na+, leading to increase in distal tubular flow rate and increase in K+ excretion

Its a wash

Question 10

How does plasma pH effect the amt. of plasma ca++ bound to plasma proteins?

Answer 10

Acidosis: LESS Ca++ is bound to plasma proteins.

Alkalosis: MORE Ca++ is bound to plasma proteins.

Question 11

List the effects of PTH(3):

Answer 11

1. Stimulates bone reabsorption
2. Stimulates activation of Vit D
3. Indirectly increases tubular Ca++ resorption

PTH is important regulator of bone uptake and release of Ca++

Question 12

How much filtered Ca++ is reabsorbed, and where in the kidney tubule does this occur?

Answer 12

99%:

• 65% in proximal tubule through paracellular route.
• 20% in proximal tubule through transcellular route

Ca++ is filtered and reabsorbed but not SECRETED

Restricted to thick ascending limb

Distal tubule

Question 13

List the factors that decrease Ca++ reabsorption:

Answer 13

Factors that decrease Ca++ excretion:

• increases levels PTH
• increase plasma [ ] of phosphate
• increase metabolic alkalosis

Look at fig 30-11: the opposite decreases Ca+ REABSORPTION:

• decrease levels of PTH
• decrease plasma [ ] of phosphate
• decrease metabolic alkalosis

Question 14

What effects do insulin and catecholamines have on extracellular K+ levels?

Answer 14

Insulin: simulates K+ uptake by cells

Catecholamines: ß-adrenergic stimulation (epinephrine)- stimulates K+ uptake by cells.
–ß-adrenergic receptor blockers->hyperkalemia

Question 15

What’re the relationships of Conn’s syndrome and addisons Dz to aldosterone secretion and K+ levels?

Answer 15

Conn’s: excess secretion of aldosterone (hypokalemia)

Addisons: deficiency in aldosterone secretion (hyperkalemia)

Question 16

What effects do metabolic acidosis, metabolic alkalosis, cell lysis, strenuous exercise, and increased extracellular fluid osmolarity have on extracellular K+ [ ] ?

Answer 16

Metabolic acidosis: increase in extracellular K+ levels, inc. H+ ion=reduction in activity of Na+K+ATPase pump=decrease in cellular uptake of K+

Metabolic alkalosis:increase in cellular uptake of K+= decreased [extracellular K+]

Cell lysis:Increases extracelullar K+

Strenuous exercise: w/ a lot of K+ released from AP/contracitons. Increases extracelullar K+

Increased extracellular fluid osmolarity: fluid flows to extracellular compartment from intracellular and brings K+ with it.

Question 17

Describe the role of the intercalated cells in controlling K+ levels.

Answer 17

Reabsorb K+ during K+ depletion:

• possibly through a H+K+ATPase pump
• secrete H+ into the tubular lumen.

Question 18

Factors that stimulate K+ secretion:

Answer 18

1. Inc extracellular fluid K+ [ ]
2. Increase in aldosterone
3. Inc tubular flow rate