Lecture 18 Renal Regulation of Ions Flashcards
Normal intracellular concentration of potassium ion is:
140 mEQ/L
Normal extracellular concentration of potassium ions is:
4.2 mEQ/L
What is the clinical significance of excess extracellular potassium?
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.
Why must the kidneys be able to rapidly adjust extracellular potassium concentration?
We have a wide variety of intake for potassium. The kidneys are the only method of adjusting for that.
What is the overall effect of aldosterone secretion on potassium excretion?
Increase in extracellular potassium stimulates increase in aldosterone secretion
What part of the renal tubule is responsible for potassium reabsorption and what part is responsible for potassium secretion?
the DISTAL renal tubules and collecting ducts will be stimulated to EXCRETE excess potassium. (aldosterone) is the key
Describe the mechanism by which principal cells secrete potassium.
.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.
What factors stimulate principal cells to secrete potassium?
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.
Describe the relationship between tubular flow rate and potassium secretion.
High potassium intake greatly increases the potassium secretion rate, even at low tubular flow rates.
Describe and explain why high sodium intake has little effect on potassium excretion.
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!
What is the overall effect of aldosterone secretion on potassium excretion?
Potassium secretion by principal cells is stimulated by potassium concentration and aldosterone.
How does plasma pH effect the amount of plasma calcium bound to plasma proteins?
Acidosis: less calcium is bound to the plasma proteins
Alkalosis: More calcium is bound to the plasma proteins
List the effects of PTH
PTH:
Stimulates bone reabsorption
Stimulates Activation of Vit. D
Indirectly increases tubular calcium reabsorption.
How much filtered Calcium is reabsorbed?
99% of filtered calcium is reabsorbed: 65% in proximal tubule.
Where in the kidney tubule does calcium reabsorption take place?
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
List the factors that decrease calcium reabsorption.
Increased Levels of PTH
Plasma concentration of phosphate
Metabolic acidosis
What effects do insulin and catecholamines have on extracellular potassium levels?
Epinephrine: Stimulates potassium uptake by cells. If you take a Beta-adrenergic receptor blocker: Hyperkalemia
What are the relationships of Conn’s syndrome and Addison’s disease to aldosterone secretion and potassium levels?
Hypokalemia: CONN’S Syndrome
Excess secretion of aldosterone
Hyperkalemia: ADDISON’S Disease
Deficiency in aldosterone
What effects do metabolic acidosis have on EC Potassium Concentration?
Increases Extracellular K+ concentration
What effects do metabolic alkalosis have on EC Potassium concentration ?
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+
What effects do cell lysis have on EC Potassium concentration ?
Hyperkalemia
What effects do strenuous exercise have on EC Potassium concentration ?
Hyperkalemia
What effects do increased extracellular laid osmolarity have on EC Potassium concentration ?
Hyperkalemia
Describe the role of intercalated cells in controlling potassium levels.
Reabsorb K+ during K+ depletion:
Possibly through a H+/K+ATPase pump, secrete H+ into tubular lumen
Increase in extracellular potassium stimulates what?
increase in aldosterone secretion from Adrenals.
Increased levels of PTH, plasma concentration of phosphate, and metabolic acidosis:
decrease calcium excretion
what would promote a decrease calcium excretion?
increased levels of PTH
increased plasma phosphate
metabolic acidosis.
Insulin and aldosterone do what?
stimulate the uptake of potassium by cells?
What two hormones would promote the uptake of potassium by a cell?
Insulin and aldosterone
Conn’s Syndrome
Hypokalemia from excess secretion of aldosterone
Addison’s disease
Hyperkalemia from a deficiency in aldosterone secretion
Almost all of the filtered calcium…
is reabsorbed by the kidney.
How much filtered calcium is excreted by the kidneys?
a. 1%
b. 47%
c. 78%
d. 99%
A. 1%
% Calcium supply is stored in the bones:
a. 1%
b. 47%
c. 78%
d. 99%
D. 99%
Major role in stimulating potassium excretion by kidney tubules: a. aldosterone b. Angiotensin II c. Sodium ion D. PTH
A. Aldosterone.
Which cells play a major role in the secretion of K+? A. intercalated B. principal cells C. chief D. Podocytes
B. Principal Cells
Which cells play a major role in the reabsorption of K+? A. intercalated B. principal cells C. chief D. Podocytes
A. Intercalated
Most K+ reabsorption occurs at which of the following sites: A. Ascending LOH B. DCT C. PCT D. Collecting Duct
C. Proximal Convoluted Tubule
A blockage of the aldosterone system would ultimately do what?
impair regulation of potassium concentration
What effects do metabolic alkalosis have on EC Potassium Concentration?
Decrease in extracellular K+ concentration
