Renal regulation of K and Ca Flashcards
(51 cards)
The vast majority of body potassium is located
In the cells
- is the most important intracellular ion
Potassium output
- urine: 92 mEq/d
- feces: 8 mEq/d
- total: 100 mEq/d
Partitioning of Na and K across cell membrane allows for
Polarity differences that are critical for excitable membranes and the development of action potentials
Intracellular dehydration
Due to loss or lack of intake leading to long term potassium wasting
How does urinary excretion of potassium range from 1 - over 100% of what was filtered at the glomerulus?
Tubules can reabsorb almost all of what was filtered to actually secreting extra potassium into the tubule on top of what was filtered
Plasma potassium only represents _____
A small fraction of whole body potassium
How to assess overall body potassium status
Measure renal potassium fractional excretion
- asses proportion of potassium filtered across the glomerulus compared to that contained in the urine
Causes of extracellular K moving into the cell
- increases K intake
- insulin
- aldosterone
- beta-adrenergic
- alkalosis
Causes of intracellular K moving out of the cell
- cell lysis
- strenuous exercise
- acidosis
- beta blockade
- HYPP
Insulin
Insulin surge after eating moves excess K just ingested from the ECF into the cell
____ and ____ tend to push K into cells
Insulin; alkalosis
Giving IV bicarb causes H ions to move out of the cells to maintain normal pH, and K moves _____ to maintain an electroneutral exchange of ions
Into cells
Cellular acidosis
Results in K moving out of the cell to maintain electroneutrality within the cell and reduce K uptake into the cell by decreasing the efficiency of the Na K ATPase pump
Patients that are inappetent and suffering from GI electrolyte losses are _____
In a negative potassium balance
The ______ is responsible for long term sustainable control of potassium
Kidney
Potassium excretion is determined by the sum of 3 renal processes:
- rate of filtration
- tubular K reabsorption/secretion
- tubular flow rate
Acute renal failure
Results in a decrease in GFR and can cause serious K accumulation and hyperkalemia due to a high potassium diet
What is the primary cell involved in potassium excretion?
Principal cells of the late distal and collecting tubules
What is the limiting factor of the Na K ATPase pump?
Electrolyte availability, NOT energy!
Aldosterone secretion is increased by
Increased serum potassium
- independent of angiotensin 2
- causes increased secretion of K into the distal tubule lumen by the principle cells
Where is the primary site of aldosterone?
On the principle cells of the cortical collecting tubule
Aldosterone feedback loop
Increased K intake –> increased plasma K concentration —> increased aldosterone (+) –> increased K secretion cortical collecting tubules –> increased K excretion
What happens to K in the absence of aldosterone secretion?
Renal secretion of K is impaired, leading to ECF potassium concentration to rise to high levels
What happens to K with excess aldosterone secretion?
Potassium secretion becomes greatly increased, causing potassium loss by the kidneys = hypokalemia
