Renal Regulation of Ion concentrations Flashcards
extracellular potassium is normally precisely regulated at
4.2 mEq/L (+0.3 mEq/L)
an extracellular potassium increase of __ to __ can lead to cardiac arrhythmias and higher can lead to
3 to 4 mEq/L. cardiac arrest or fibrillation
Extracellular fluid contains ___ % of total body potassium
2%
intake of potassium form a single meal can be as high as
50 mEq
____ must adjust potassium excretion rapidly and precisely in response to wide variations in intake
kidneys (mainly involves distal and collecting tubules)
What is mainly involved in kidneys adjusting potassium excretion
distal and collecting tubules
What is the normal intracellular concentration of potassium ion
140 mEQ/L
Total amount of extracellular potassium
4.2 mEq/L x 14 L = 59 mEq
Total amount of intracellular potassium
140 mEq/L x 28 L= 3920 mEq
Major factors responsible for potassium excretion
- Direct influence on distal renal tubules and collecting ducts via increase in extracellular potassium ion concentration
- Effect of aldosterone secretion on potassium excretion
- increase in extracellular potassium stimulates increase in aldosterone secretion
An increase in extracellular potassium stimulates a _____ in aldosterone secretion
increase
potassium daily intake is equal to
100 mEq/day
Potassium daily output in urine and feces
urine- 92 mEq/day
Feces- 8 mEq/Day
Sites of potassium reabsorption
- proximal tubule
- Ascending limb of Henle
Sites for the secretion of potassium in the nephron
- Late tubule
- Collecting duct
potassium secretion by principle cells is stimulated by
potassium concentration and aldosterone
Treatment of hypertension with Beta-Adrenergic receptor blockers, such as propranolol, causes potassium to
-move out of the cells and creates a tendency toward hyperkalemia
What __ % of filtered potassium is reabsorbed in the proximal tubule
65%
What % of filtered potassium is reabsorbed in the loop of Henle
25-30% (especially in the thick ascending part where potassium is actively co-transported along with sodium and chloride)
Cells in the late distal and cortical collecting tubules that secrete potassium are called
principle cells
explain how principle cells excrete potassium into tubular lumen
Sodium-potassium ATPase on the basolateral side exchanges potassium for sodium. The increase in potassium inside the cell leaves to a passive diffusion of potassium from the interior of the cell into the tubular fluid
How does aldosterone effect extracellular potassium levels
Aldosterone stimulates active reabsorption of sodium ions by the principle cells of the late distal tubules and collecting ducts
as aldosterone levels and extracellular K+ levels increase what happens to the urinary potassium excretion
it increases
small changes in serum potassium concentration cause ____ changes in aldosterone by adrenals
large
what is the direct and indirect way that high potassium intake raises potassium excretion
- Direct influence on kidneys via high potassium concentration
- Indirect via aldosterone secretion
high potassium intake _____ the potassium secretion rate even at low tubular flow rates
greatly increases
A rise in distal tubular flow rate does what to potassium secretion
stimulates potassium secretion
explain how high sodium intake has a counterbalance effect on potassium secretion
High sodium intake leads to a decreased aldosterone secretion and thus decrease potassium secretion. But increased sodium intake also leads to increase in GFR and Decrease in proximal tubular Na reabsorption, which leads to increased distal tubular flow and increased potassium secretion.
A High sodium diet leads to ____ change in potassium excretion
little.
Explain how low sodium intake has a counterbalance effect on potassium secretion
-increase in aldosterone—> increase potassium secretion
also decreases GFR and distal tubular flow rate thus decreased potassium excretion
between the two there is now change in potassium secretion
about 50% of total plasma calcium is in the ___ form
ionized form (ionized has biological activity at cell membraes)
Acidosis has what changes on calcium binding
less calcium is bound to the plasma proteins
Alkalosis has what changes on calcium binding
more calcium is bound to the plasma proteins
A large amount of calcium is excretion occurs in the
feces; therefore, GI tract is important in calcium homeostasis
Almost all calcium in the body is stored in
the bones
____ is one of the most important regulators of bone uptake and release of calcium
PTH (parathyroid hormone)
Parathyroid glands are directly stimulated by
low calcium levels
Low calcium levels increase the secretion of
PTH (parathyroid hormone)
Parathyroid hormone effects
- stimulates bone reabsorption
- stimulates activation of Vitamin D
- Indirectly increases tubular calcium reabsorption
About __% of filtered calcium is reabsorbed in the proximal tubule.
99%
What percentage of filtered calcium is reabsorbed in the proximal tubule through the paracellular route
65%
What percentage of filtered calcium is reabsorbed in the proximal tubule through the transcellular route
20%
How is calcium reabsorbed in the proximal tubule by the transcellular route
- electrochemical gradient
- Basolateral calcium-ATPase and sodium-calcium counter-transport
Calcium reabsorption in the loop of Henle is restricted to the
thick ascending limb
of the calcium reabsorbed in the thick ascending loop of Henle what percent is through the paracellular route
50% (passive diffusion and slight positive charge of tubular lumen)
of the calcium reabsorbed in the thick ascending loop of Henle what percent is through the transcellular route and is stimulated by
50% stimulated by PTH (parathyroid hormone)
Calcium reabsorption in the distal tubule is almost entirely via _____ transport in the ____ membrane
active transport (calcium-ATPase pump) in the basolateral membrane
Calcium reabsorption in the distal tubule is stimulated by
PTH (parathyroid hormone)
Factors that regulate tubular calcium reabsorption
- PTH
- plasma concentration of calcium
- metabolic acidosis
Factors that increase calcium excretion
- decrease in PTH
- Increase in extracellular fluid volume
- increase in blood pressure
- decrease in plasma phosphate
- Metabolic acidosis
Factors that decrease calcium excretion
- Increase in PTH
- Decrease in extracellular fluid volume
- decrease in blood pressure
- increase in plasma phosphate
- metabolic alkalosis
- Vitamin D3
compensatory responses to decrease plasma ionized calcium concentration is mediated by
PTH
Vitamin D3 is activated by
increase in PTH
Vitamin D3 functions in
increasing intestinal calcium reabsorption
who does the calcium exhanger in the proximal tubular cells work
3 sodium in and 1 calcium out (into the renal interstitial fluid)
phosphate transport maximum for reabsorption equals
0.1 mM/min
phosphate excretion by the kidneys is controlled primarily by an
overflow mechanism
phosphate normally begins to spill into the urine when its concentration in the extracellular fluid rises above a threshold of about
0.8 mM/L
When less than .1mmol of phosphate is present in the glomerular filtrate than
essentially all the filtered phosphate is reabsorbed
When more than .1 mmol of phosphate is present in the glomerular filtrate than
the excess (over .1mmol) is secreted
____ % of phosphate is reabsorbed in the proximal tubule via what pathway
75%-80%, transcellular
___% fo phosphate is reabsorbed in the distal tubule
10%
how does PTH effect phosphate concentrations
- PTH promotes bone reabsorption and thus an increase in phosphate in the extracellular fluid-
- PTH decreases transport maximum for phosphate by renal tubules —> greater loss of phosphate in urine
Whenever plasma PTH is ____ , tubular reabsorption is decreased and more phosphate is excreted.
increased
extracellular fluid potassium concentration normally is maintained at
4.2 (plus or minus 0.3 mEq/L)
only ___ % of the total body potassium is in the extracellular fluid
2%
____ must be able to adjust potassium excretion rapidly
Kidneys
____, ____, and _____ stimulate potassium uptake by cells
Insulin, aldosterone, beta-adrenergic stimulation (epinephrine)
What is conn’s syndrome. What does it lead to
increased secretion of aldosterone. Leads to hypokalemia
What is Addison’s disease?
is adrenal insufficiency
decreased levels of aldosterone leads to hyperkalemia
Aldosterone stimulates active reabsorption of Na+ by _____ cells via sodium-potassium-ATPase pump
principle cells
Can beta-adrenergic receptor blockers lead to hyperkalemia
yes
____ potassium intake stimulates aldosterone secretion
increase
metabolic acidosis has what effect on extracellular potassium concentration
increases extracellular potassium concentration
metabolic alkalosis has what effect on extracellular potassium concentration
decreases extracellular potassium concentration
Cell lysis, strenuous exercise, and increased extracellular fluid osmolarity have what effect on extracellular potassium concentration
hyperkalemia
increased H+ concentration —-> reduction in activity of ________ pump —-> decrease in cellular uptake of potassium
Na+-K+ ATPase pump
What is the rate of potassium filtration
Normal= 180 L/day x 4.2 mEq/L= 756 mEq/day
what is the rate of potassium reabsorption in the proximal tubule (%)
65%
What percent of potassium is reabsorbed in the loop of Henle
25-30%
90% of the cells in the late distal tubule and cortical collecting tubules are
principle cells
Principle cells in the late distal tubule and cortical collecting tubules have what function
Secrete potassium into tubular fluid
- have Na+-K+-ATPase pump in basolateral membrane
- passive diffusion of K+ into tubular lumen
What factors stimulate potassium secretion in the principle cells
- increase in extracellular fluid potassium concentration
- stimulates Na+-K+-ATPase
- increase potassium gradient from ECF to cellular fluid
- stimulates aldosterone secretion
- increase aldosterone
- tubular flow rate
What are the controls of Potassium secretion
- activity of Na+-K+ ATPase pump
- electrochemical gradients
- permeability of luminal membrane
What is the role of intercalated cells
- Reabsorb K+ during K+ depletion:
- possibly through a H+-K+-ATPase
- secrete H+ into tubular lumen
Most of the potassium reabsorption occurs at
proximal convoluted tubule
what type of cells play a major role in the secretion of potassium
principle cells
Approximately how much of the body’s supply of calcium is stored in the bone
99%
how much of the filtered calcium is secreted by the kidneys
1%
What cells reabsorb potassium during potassium depletions
intercalated cells
a high potassium intake would have what effect on potassium excretion associated with increased renal tubular flow rate
-potassium excretion would increase with an increase in tubular flow rate
which of the following describes a valid change in potassium distribution due to an acid-base abnormality?
A.) metabolic acidosis decreases extracellular K+ concentration
B.) Metabolic alkalosis increases extracellular K+ concentration
C.) metabolic acidosis increases extracellular K+ concentration
D. both A and B are valid
C.) Metabolic acidosis increases extracellular K+ concentration
At high levels of angiotensin II greater _______ in arterial pressure are necessary to ______ sodium excretion
increases, increase
at reduced angiotensin II levels, normal levels of sodium can be maintained at ______ arterial pressures
reduced
Blood volume ___________ in normal range of daily fluid intakes
remains relatively normal
