Guyton - Chapter 29: Renal Regulation Of Potassium Flashcards
How much of the body’s potassium is in the cells and how much is in the extracellular fluid?
98% of the total body potassium is contained in the cells and only 2% is in the extracellular fluid.
How does insulin affect potassium?
Insulin stimulates potassium uptake into cells.
How is aldosterone and potassium connected?
Increased potassium intake stimulates secretion of aldosterone which increases cells potassium uptake.
How is catecholamines and potassium connected?
Catecholamines especially epinephrine can cause movement of potassium from the extracellular to the intracellular fluid mainly by activation of B-adrenergic receptors.
How is acid-base abnormalities connected to potassium distribution?
Metabolic acidosis increases extracellular potassium concentration in part by causing loss of potassium from the cells whereas metabolic alkalosis decreases extracellular fluid potassium concentration.
How is increased extracellular fluid osmolarity connected to potassium?
Increased extracellular fluid osmolarity causes osmotic flow of water out of the cells. The cellular dehydration increases intracellular potassium concentration, thereby promoting diffusion of potassium out of the cells and increasing extracellular fluid potassium concentration. Decreased extracellular fluid osmolarity has the opposite effect.
What happens to potassium in the tubules?
Potassium is reabsorbed in the proximal tubule and in the ascending loop of Henle so only about 8% of the filtered load is delivered to the distal tubule. Secretion of potassium into the late distal tubules and collecting ducts adds to the amount delivered. Therefore the daily excretion is about 12% of the potassium filtered at the glomerular capillaries.
Where is the most important site for regulating potassium excretion?
The principal cells of the late distal tubules and the cortical collecting tubules. In these tubular segments, potassium can at times be reabsorbed or at other times be secreted depending on the needs of the body.
Where does most of the day-to-day regulation of potassium excretion occurs?
It occurs in the late distal and cortical collecting tubules where potassium can be either reabsorbed or secreted depending on the needs of the body.
Describe the two-step process of secretion of potassium from the blood into the tubular lumen.
It begins with uptake from the interstitium into the cell by the sodium-potassium ATPase pump in the basolateral cell membrane: this pump moves sodium out of the cell into the interstitium and at the same time moves potassium to the inferior of the cell. The second step of the process is passive diffusion of potassium from the inferior of the cell into the tubular fluid. The luminal membrane of the principal cells is highly permeable to potassium.
What are the primary factors that control potassium secretion by the principal cells of the late distal and cortical collecting tubules?
- The activity of the sodium-potassium ATP:ase pump
- The electrochemical gradient for potassium secretion from the blood to the tubular lumen.
- The permeability of the luminal membrane for potassium.
Which cells can reabsorb potassium during potassium depletion?
Intercalated cells in the late distal and collecting tubules.
What are the 3 most important factors that stimulate potassium secretion by the principal cells?
- Increased extracellular fluid potassium concentration
- Increased aldosterone
- Increased tubular flow rate
One factor that DECREASES potassium secretion is increased hydrogen ion concentration (acidosis).
What are the 3 mechanisms that makes increased extracellular fluid potassium concentration to raise potassium secretion?
- Increased extracellular fluid potassium concentration stimulates the sodium-potassium ATPase pump thereby increasing potassium uptake across the basolateral membrane. This in turn increases intracellular potassium ion concentration causin diffusion to diffuse across the luminal membrane into the tubule.
- Increased extracellular potassium concentration increases the potassium gradient from the renal interstitial fluid to the interior of the epithelial cell, this reduces back leakage of potassium ions from inside the cells through the basolateral membrane.
- Increased potassium concentration stimulates aldosterone secretion by the adrenal cortex which further stimulates potassium secretion.
How does aldosterone stimulate active reabsorption of sodium ions and how is the effect mediated?
Aldosterone stimulates active reabsorption of sodium ions by the principal cells of the late distal tubules and collecting ducts. This effect is mediated through a sodium-potassium ATP:ase that transports sodium outward through the basolateral membrane of the cell and into the blood at the same time that it pumps potassium into the cell.
A second effect of aldosterone is to increase the permeability of the luminal membrane for potassium further adding to the effectiveness of aldosterone in stimulating potassium secretion.
What does aldosterone do more than add to a stimulatory effect on renal secretion of potassium?
Aldosterone also increases cellular uptake of potassium.
What happens with potassium when there is a rise in distal tubular flow rate?
It stimulates potassium secretion.
What happens with potassium secretion in acute acidosis and alkalosis?
Acute increases in hydrogen concentration of the extracellular fluid (acidosis) reduces potassium secretion whereas alkalosis increases potassium secretion.
