Potassium metabolism - Showkat Flashcards
Where is the majority of potassium in the body?
ICF - muscle
What routes excrete potassium?
Renal (90%)
GI (10%)
Where is potassium excreted in the nephron?
CD (principal cells) - ROMK (renal outer medullary) channel
Where is potassium reabsorbed in the nephron?
TALH- NaK2Cl and paracellularly
What factors affect potassium secretion in the distal tubule?
Concentration gradient (based on serum [K]) Electrical gradient (based on [Na] in lumen) K permeability (based on aldosterone)
What are causes of decreased renal potassium secretion?
Renal failure
Distal tubular dysfunction
Decreased distal tubular flow
Hypoaldosteronism
What are causes of increased renal potassium secretion?
Bartter's syndrome / Gitelman's Syndrome (Increased Na delivery) Diuretics Hyperaldosteronism (prolonged vomiting or nasogastric suction)
What factors affect internal potassium balance?
Plasma potassium concentration Insulin Epinephrine Acid-Base disturbance Plasma Tonicity Cell Lysis and Proliferation
How do changes in extracellular pH produce affect K?
Reciprocal shifts in H and K
What are the relative extracellular potassium concentrations in extracellular acidosis and alkalosis?
Acidosis - Hyperkalemia
Alkalosis - Hypokalemia
Loss of intracellular water or plasma hypertonicity would have what effect on K?
Potassium would leave the cell via solvent drag
What would the effects of cell lysis or proliferation have on extracellular potassium?
Lysis (Rhabdomyolysis, hemolysis) - Increased extracellular potassium
Proliferation - Decreased extracellular potassium
What are three major causes of potassium concentration?
Intake
Excretion
Internal Distribution
What are causes of internal redistribution that would produce hyperkalemia?
Insuline deficiency Beta2-Adrenergic blockade Hypertonicity Acidemia Cell lysis
What are signs of hyperkalemia?
Peaked T-wave Wide QRS complex Absent P-wave Sine-wave morphology Bradyarrythmias
What is the treatment for hyperkalemia?
Stabilize cardiac muscle - IV Ca Insulin Beta agonist Bicarbonate Diuretics Resins (GI tract) Dialysis
What is the quickest and slowest acting treatment of hyperkalemia?
Quickest - Calcium
Slowest - Resin
What are causes of internal redistribution that would produce hypokalemia?
Insulin excess
Catecholamine excess (epinephrine)
Alkalemia
Cell proliferation
What causes normotensive hypokalemia?
Renal loss
Alkalosis - diuretics, vomiting, nasogastric suction, barter’s / gitelman’s syndrome
Acidosis - renal tubular acidosis 1/2, ureteral diversion
How and where do thiazides act?
Block NaCl reabsorption in DCT
How and where does RTA I act?
Increase K secretion in CD
How and where does RTA II act?
Block reabsorption in PCT
How and where does Gitelman’s act?
Blocks NaCl reabsorption in DCT
How and where does Bartter’s act?
Block NaKCl transporter reabsorption in TALH
How and where do Furosemides act?
Block NaKCl transporter reabsorption in TALH
What causes hypertensive hypokalemia?
Hyperreninemia Praimary hyperaldosteronism (Conn's syndrome) Cushing's syndrome (Glucocorticoid excess - acts like aldosterone) Congenital adrenal hyperplasia (excess aldosterone precursors)
What are the signs of hypokalemia?
Prominent U wave
Tachyarrythmias
Nephrogenic diabetes insipidus
What is the treatment of hypokalemia?
Potassium replacement (KCl or KPO4) Potassium sparing diuretics
What are the types of potassium sparing diuretics?
Epithelial Na Channel (ENAC) inhibitors - Amiloride, Triamterene
Mineralocorticoid antagonists - Spironolactone, Eplerenone
