Lecture 18 Renal Regulation of Ions

Question 1

Normal intracellular concentration of potassium ion is:

Answer 1

140 mEQ/L

Question 2

Normal extracellular concentration of potassium ions is:

Answer 2

4.2 mEQ/L

Question 3

What is the clinical significance of excess extracellular potassium?

Answer 3

Extracellular potassium is regulated precisely at 4.2 mEq/L. An increase can lead to cardiac arrhythmia, even higher can lead to cardiac arrest or fibrillation.

Question 4

Why must the kidneys be able to rapidly adjust extracellular potassium concentration?

Answer 4

We have a wide variety of intake for potassium. The kidneys are the only method of adjusting for that.

Question 5

What is the overall effect of aldosterone secretion on potassium excretion?

Answer 5

Increase in extracellular potassium stimulates increase in aldosterone secretion

Question 6

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

Answer 6

the DISTAL renal tubules and collecting ducts will be stimulated to EXCRETE excess potassium. (aldosterone) is the key

Question 7

Describe the mechanism by which principal cells secrete potassium.

Answer 7

.Potassium secretion and Sodium reabsorption done by principal cells. The potassium secretion is stimulated by the potassium concentration and aldosterone.

On the apical side: Na+/K+ ATP exchanger. Lumen side: ENaC brings Sodium in, and Potassium goes out.

Question 8

What factors stimulate principal cells to secrete potassium?

Answer 8

High potassium intake raises potassium excretion. Direct influence on kidneys via high K concentration, Indirect via aldosterone secretion. Very small changes in potassium concentration will cause a LARGE change in aldosterone secretion by adrenals.

Question 9

Describe the relationship between tubular flow rate and potassium secretion.

Answer 9

High potassium intake greatly increases the potassium secretion rate, even at low tubular flow rates.

Question 10

Describe and explain why high sodium intake has little effect on potassium excretion.

Answer 10

Increased sodium intake causes decreased aldosterone secretion. THEREFORE it will cause Cortical collecting ducts to KEEP the Potassium. This is counteracted by: Increase in sodium causing increased GFR and Lowered Sodium absorption in the proximal tubule … this will cause the distal tubular flow rate to increase, but also increase K+ secretion in the cortical collecting ducts, and therefore the K+ excretion will be unchanged!

Question 11

What is the overall effect of aldosterone secretion on potassium excretion?

Answer 11

Potassium secretion by principal cells is stimulated by potassium concentration and aldosterone.

Question 12

How does plasma pH effect the amount of plasma calcium bound to plasma proteins?

Answer 12

Acidosis: less calcium is bound to the plasma proteins
Alkalosis: More calcium is bound to the plasma proteins

Question 13

List the effects of PTH

Answer 13

PTH:
Stimulates bone reabsorption
Stimulates Activation of Vit. D
Indirectly increases tubular calcium reabsorption.

Question 14

How much filtered Calcium is reabsorbed?

Answer 14

99% of filtered calcium is reabsorbed: 65% in proximal tubule.

Question 15

Where in the kidney tubule does calcium reabsorption take place?

Answer 15

65% of it happens in proximal tubule via paracellular route.
20% in the proximal tubule via transcellular route. using Electrochemical gradient and Basolateral calcium-ATPase and Sodium-Calcium Counter transporter.

Calcium Reabsorption is restricted to thick ascending limb: 50% through paracellular route
…passive diffusion and slight positive charge of tubular lumen.

50% via transcellular route stimulated by PTH

Question 16

List the factors that decrease calcium reabsorption.

Answer 16

Increased Levels of PTH
Plasma concentration of phosphate
Metabolic acidosis

Question 17

What effects do insulin and catecholamines have on extracellular potassium levels?

Answer 17

Epinephrine: Stimulates potassium uptake by cells. If you take a Beta-adrenergic receptor blocker: Hyperkalemia

Question 18

What are the relationships of Conn’s syndrome and Addison’s disease to aldosterone secretion and potassium levels?

Answer 18

Hypokalemia: CONN’S Syndrome
Excess secretion of aldosterone

Hyperkalemia: ADDISON’S Disease
Deficiency in aldosterone

Question 19

What effects do metabolic acidosis have on EC Potassium Concentration?

Answer 19

Increases Extracellular K+ concentration

Question 20

What effects do metabolic alkalosis have on EC Potassium concentration ?

Answer 20

Increase in EC K+ Concentration, and increase in H+ concentration, leads to a reduction in activity of Sodium/Potassium ATPASE pump and that will lead to a decrease in cellular uptake of K+

Question 21

What effects do cell lysis have on EC Potassium concentration ?

Answer 21

Hyperkalemia

Question 22

What effects do strenuous exercise have on EC Potassium concentration ?

Answer 22

Hyperkalemia

Question 23

What effects do increased extracellular laid osmolarity have on EC Potassium concentration ?

Answer 23

Hyperkalemia

Question 24

Describe the role of intercalated cells in controlling potassium levels.

Answer 24

Reabsorb K+ during K+ depletion:

Possibly through a H+/K+ATPase pump, secrete H+ into tubular lumen

Question 25

Increase in extracellular potassium stimulates what?

Answer 25

increase in aldosterone secretion from Adrenals.

Question 26

Increased levels of PTH, plasma concentration of phosphate, and metabolic acidosis:

Answer 26

decrease calcium excretion

Question 27

what would promote a decrease calcium excretion?

Answer 27

increased levels of PTH increased plasma phosphate metabolic acidosis.

Question 28

Insulin and aldosterone do what?

Answer 28

stimulate the uptake of potassium by cells?

Question 29

What two hormones would promote the uptake of potassium by a cell?

Answer 29

Insulin and aldosterone

Question 30

Conn's Syndrome

Answer 30

Hypokalemia from excess secretion of aldosterone

Question 31

Addison's disease

Answer 31

Hyperkalemia from a deficiency in aldosterone secretion

Question 32

Almost all of the filtered calcium...

Answer 32

is reabsorbed by the kidney.

Question 33

How much filtered calcium is excreted by the kidneys? a. 1% b. 47% c. 78% d. 99%

Answer 33

A. 1%

Question 34

% Calcium supply is stored in the bones: a. 1% b. 47% c. 78% d. 99%

Answer 34

D. 99%

Question 35

``` Major role in stimulating potassium excretion by kidney tubules: a. aldosterone b. Angiotensin II c. Sodium ion D. PTH ```

Answer 35

A. Aldosterone.

Question 36

``` Which cells play a major role in the secretion of K+? A. intercalated B. principal cells C. chief D. Podocytes ```

Answer 36

B. Principal Cells

Question 37

``` Which cells play a major role in the reabsorption of K+? A. intercalated B. principal cells C. chief D. Podocytes ```

Answer 37

A. Intercalated

Question 38

``` Most K+ reabsorption occurs at which of the following sites: A. Ascending LOH B. DCT C. PCT D. Collecting Duct ```

Answer 38

C. Proximal Convoluted Tubule

Question 39

A blockage of the aldosterone system would ultimately do what?

Answer 39

impair regulation of potassium concentration

Question 40

What effects do metabolic alkalosis have on EC Potassium Concentration?

Answer 40

Decrease in extracellular K+ concentration