Final: Lecture 18 Flashcards
Factors that shift K+ into cells (decrease extracellular K+)
- Insulin
- Aldosterone
- ß-adrenergic stimulation
- Alkalosis
What is the normal intracellular concentration of K+ ion?
•140 mEQ/L
Factors that shift K+ out of cells (Increase extracellular K+)
- Insulin and aldosterone deficiency
- ß-adrenergic blockade
- Acidosis and cell lysis
- Strenuous exercise
- Increased extracellular fluid osmolarity
Major factors responsible for K+ excretion?
- Direct influence on distal renal tubules and collecting ducts via increase in extracellular K+ ion concentration
- Effect of aldosterone secretion on K+ excretion
What are the two sites of K+ reabsorption?
•Proximal tubule and Ascending limb of Henle
What are the two sites of K+ secretion?
•late tubule and collecting duct
Mechanisms of K+ secretion and Na+ reabsorption and secretion are by?
•Principal cells
Small changes in K+ concentration cause ______ changes in aldosterone secretion by adrenals.
•Large
Acidosis, _______ Ca is bound to plasma proteins, while in Alkalosis ______ Ca is bound.
- Less
* More
Almost all the Ca in the body is stored in the _______.
•bone
________ is one of the most important regulators of bone uptake and release of Ca.
- PTH (parathyroid hormone)
* Parathyroid glands are directly stimulated by low Ca levels
PTH effects
- Stimulates bone reabsorption
- Stimulates activation of vitamin D
- Indirectly increases tubular Ca+ reabsorption
Reabsorption in the proximal tubule
•99% of filtered Ca reabsorbed, 65% through paracellular, 20% through transcellular
Ca Reabsorption in loop of Henle
- Restricted to thick ascending limb
- 50% thought paracellular, passive diffusion and slight positive charge of tubular lumen
- 50% via transcellular, stimulated by PTH (pumps Na/Ca)
Ca reabsorption in distal tubule
- Almost entirely via active transport
- Ca-ATPase pump in basolateral membrane
- Stimulated by PTH
Factors that regulate tubular Ca reabsorption
- Increase levels of PTH
- Plasma concentration of Ca
- Metabolic acidosis
- All decreases Ca excretion
Phosphate Excretion
- Controlled by overflow mechanism, all filtered reabsorbed excess is secreted
- 75-80% reabsorbed in proximal tubule, transcellular
- 10% in distal tubule
_______ stimulates K+ uptake by cells
•Insulin
________ increases K+ uptake by cells
- Aldosterone
- Stimulates active reabsorption of Na by principal cells via Na-K-ATPase pump
- Increase permeability of luminal membrane K+
- Increase extracellular K+—> aldosterone secretion
Hypokalemia is _________ secretion of aldosterone.
•Excess
Hyperkalemia is _______ in aldosterone secretion.
•Deficiency
Catecholamines
- ß-adrenergic stimulation (epinephrine), stimulates K+ uptake by cells
- ß-adrenergic receptor blockers–> hyperkalemia
What 4 things can result in hyperkalemia?
- Metabolic alkalosis–>decrease extracellular K+
- Cell lysis
- Strenuous exercise
- Increased extracellular fluid osmolarity
Principal Cells
- Found in late distal tubule and cortical collecting tubules, 90% of cells in these regions
- Secrete K+, passive diffusion of K+ into tubular lumen, could end up in urine
Intercalated cells
- Reabsorb K+ during K+ depletion
- possibly through a H+-K+-ATPase pump
- Secrete H+ into tubular lumen
