renal regulation of ion concentrations Flashcards
What’s the normal concentration of extracellular potassium? What can happen if it increases?
4.2 mEq/L
Increased 3-4 mEq can lead to cardiac arrythmias
Any higher -> cardiac arrest or fibrillation
What’s the typical concentration of intracellular potassium?
140 mEq/L
How does aldostrone effect potassium excretion?
Increases extracellular potassium which stimulates even more aldostrone secretion
What portions of the nephron reabsorb potassium?
Proximal tubule
Ascending limb of Henle
Which portions the nephron secrete potassium?
Late tubule
Collecting duct
How do principal cells go about secreting potassium?
Uptake of pot. From the interstitial fluid by Na+K+ pump. Potassium flows out the BK and ROMK channels on the tubular lumen side.
Stimulated by potassium concentration and aldostrone
How does flow rate relate to potassium secretion?
Also depends on potassium intake
In a high potassium diet, there is high secretion of potassium while the flow rate doesnt increase that much.
In low potassium diet lots of flow rate doesnt greatly increase secretion rate
In a normal diet, the flow rate and the potassium secretion rate increase at the same time.
Why does eating alot of salt not effect potassium secretion?
Because Na+ decreases aldostrone which negatively effects K+ secreting cortical collecting ducts.
It also decreases proximal tubular Na+ reabsorption which increase distal tubular flow rate which stimulated the K+ secreting cortical collecting ducts.
The effect null eachother
How does plasma pH effect calcium binding?
In Acidosis: less calcium is bound to the plasma protein
In Alkalosis: more calcium is bound to the plasma protiens.
About 50% of plasma Calcium is in the ionized form.
What are the effects of Parathyroid hormone?
Stimulates bone reabsorption (Ca++ released from bones)
Stimulates activation of vitamin D - which increases intestinal Ca++ reabsorption
Indirectly increases tubular calcium reabsorption
How much of the filtered calcium is reabsorbed in the kidneys?
99%
65% - proximal tubule: paracellular route
20% - proximal tubule: transcellular route.
More reabsorption in the thick ascending limp of the loop of Henle.
How is phosphate excretion controlled? What are the effects of PTH?
Controlled by overflow mechanism
-> when the concentration is below the transport maximum for potassium (0.1 mM/min) then all filtered phosphate is reabsorbed. If it’s more than the excess is secreted.
PTH promotes bone reabsorption and increase phosphate in extracellular fluid.
It also lowers to transport maximum by the renal tubules which increases the loss of phosphate in urine.
How does insulin and catecholamine effect regulation of extracellular potassium? Q
Insulin: stimulating potassium uptake by cells
Catecholamines: b-adrenal stimulation (by epinphrine) stimulates potassium uptake by cells. Blocking the receptors -> hyperkalemia
Aldostrone, which increase potassium uptake by cells, is associated with hyponatremia and hyperkalemia. What are the associated condiations, and the aldostrone levels in each?
Hypokalemia: excess secretion of aldostrone - Conn’s syndrome
Hyperkalemia: deficiency in aldosterone secretion, Addison’s disease
+potassium in extracellular fluids
What effect do each of these have on extracellular concentration of potassium?
Metabolic acidosis
Metabolic alkalosis
Cell lysis
Strenuous exercise
Increased extracellular fluid osmolarity
Metabolic acidosis - increases
Metabolic alkalosis - decreases
Cell lysis - increase
Strenuous exercise - increase
Increased extracellular fluid osmolarity- increases
