Control of K, Ca, PO3, Mg- Exam 4 Flashcards
Potassium is tightly controlled. Usually changes less that what concentration?
+/- 0.3 mEq/L
Cell functions are very sensitive to changes in concentration of what ion?
Potassium; resting membrane potentials
What percent of potassium is located in the intracellular volume?
98%
What percent of potassium is located in the extracellular volume?
2%
What is the daily intake of potassium?
50 mEq/L - 200 mEq/L
Small changes in extracellular K+ can easily lead to what?
Hyper or hypokalemia
What percent of potassium intake is removed by feces?
5-10%
Potassium not removed by the feces must be removed how?
Kidneys
What is the first line of defense against changes in extracellular concentration of potassium?
Movement between intra and extracellular compartments possible
After ingesting 40 mEq of K+ into ECF, [K+] would increased by how much?
2.8 mEq/L
Most ingested K+ quickly moves where?
Into the cellular volume
What moves potassium and glucose into the cells following a meal?
Insulin
Increased [K+] stimulates secretion of what?
Aldosterone
What could affect ability to move K+ into the cells and K+ reabsorption?
Disease state
What stimulates B2-adrenergic receptors?
Epinephrine
What happens when epinephrine stimulates B2-adrenergic receptors?
Increasing movement of K+ into the cell.
What receptors do hypertension tx’s block?
B2- adrenergic blocking agents
B2-adrenergic blocking agents can lead to what condition?
Hyperkalemia
What are some potential factors that shift K+ into the cells?
Insulin
Aldosterone (K+ secretion)
B-adrenergic stimulation
Alkalosis
What are some factors that shift K+ out of cells?
Insulin deficiency (DM) Aldosterone deficiency (Addision's Disease) B-adrenergic blockade Acidosis Cell lysis Strenuous exercise Increased extracellular fluid osmolarity
Increased [H+] will reduce the action of what pump? What does this result in?
Na-K ATPase; less transfer of K+ into the cells
What does cell lysis result in?
Dumps intracellular K+ in extracellular compartment
An increase in extracellular osmolarity, ________ moves out of the cell, increasing intracellular [K+], which increases the rate of ________ diffusion out of the cell.
water, K+
What three things determine excretion rate?
Rate of potassium filtration
Rate of potassium reabsorption
Rate of potassium secretion
What is the fraction of filtered load reabsorbed in the proximal tubule and loop of Henle day to day?
Constant; does not change day-to-day
Calculate the filtration of potassium.
180L/day x 4.2 mEq/L = 756 mEq/day
What percent of potassium is reabsorbed in the proximal tubule?
65%
What percent of potassium is reabsorbed in the loop? Mainly what segment?
25-30%; thick ascending segment
Flexible reabsorption and secretion of potassium utilizing what cells? Where are these cells located?
Principle cells; distal tubule and cortical collecting tubule
What is the normal intake of K+? How is removed?
100 mEq/day; 8mEq removed in feces; 92mEq removed in kidneys
Proximal tubule removes what concentration of potassium? Leaving how much?
491 mEq; leaving 265 mEq
Loop removes what concentration of ptassium? leaving how much?
Loop removes 204 mEq leaving 61 mEq
Distal tubule and cortical collecting tubule must secrete how much potassium? What fraction of excreted potassium?
31mEq; 1/3 of excreted potassium
During high potassium intake, what part of the nephron increases potassium secretion?
Distal tubule and cortical collecting tubule; very strong mechanism (rate of potassium excretion can exceed amount of potassium being filtered)
During low potassium intake, what decreases?
Secretion; can decrease to a point where this is net reabsorption
During low potassium intake, excretion can fall to what percent of filtered potassium?
1% (756 mEq/day x 0.01 = 8 mEq/day)
What cells make up 90% of cells in late distal and cortical collecting tubule?
Principle cells
Secretion driven by what pump? where?
Na-K ATPase; basolateral border of cells; move K+ into cell setting up concentration gradient; drives diffusion from cell into tubular lumen
What membrane contains special channels for K+ diffusion?
Tubular membrane; usually provides high permeability for K+ movement out of the cell
What cells reabsorb potassium, especially during potassium depletion?
Intercalated Cells
Reabsorption of potassium by intercalated cells could be related to what pump?
H-K ATPase
Where is the H-K ATPase pump located?
Tubular membrane
Where does H-K ATPase pump H+?
From tubular cell into lumen (secretion)
Where does H-K ATPase pump K+?
Tubular lumen into cell (reabsorption)
Where does K+ diffuse?
From cell into interstitial space via basolateral membrane
When does H-K ATPase have a major effect?
Only during potassium depletion
What three factors control the rate of K+ secretion?
Activity of Na-K ATPase
Electrochemical gradient for K+ from blood into tubular lumen
Permeability of tubular membrane to K+
What stimulates potassium secretion?
Increased extracellular [K+]
Increased [aldosterone]
Increased tubular flow rate
What will decrease potassium secretion?
Increased [H+]
T/F: There is always a certain level of secretion even at normal [K+].
True
Increased [K+] stimulates action of what pump? Where is K+ moved?
Na-K ATPase; More K+ moved into cell from interstitial space which increased gradient from cell interior to tubular lumen
Increased [K+] in plasma stimulates release of what hormone?
Aldosterone
Increased aldosterone increases rate of what reabsoprtion? Where in the nephron?
Rate of sodium reabsorption; late distal tubule and collecting duct
Increased aldosterone increases activity of what pump?
Na-K ATPase; so increase in sodium reabsorption will also increase potassium secretion
Increased Aldosterone increases membrane permeability for what?
Potassium
What is an example of negative feedback control system?
Plasma Potassium & Aldosterone
Small change in [K+] produces huge change in what?
Aldosterone concentration
What is the normal aldosterone level?
6 nag/dL
Anything that affects our ability to produce aldosterone will have a big effect on excretion of what?
Potassium
High aldosterone (primary aldosteronism) leads to what?
Hypokalemia
Low aldosterone (Addison’s disease) leads to what?
Hyperkalemia
In an experiment with dogs, increased K+ intake with intact aldosterone feedback resulted in what change in intake resulting in hwat change in [K+]?
Big change in intake (x7 increase)
Small change [K+] (4.2 - 4.3 mEq/L)
In an experiment with dogs, increased K+ intake with BLOCKED aldosterone feed back resulting in what change in intake result in what change in [K+]?
Big change in intake (x7 increase)
Big change in [K+] (3.8 - 4.7 mEq/L)
Increased flow where will increase potassium secretion?
Distal tubular flow
Increased tubular flow can be caused by what?
Volume expansion; high sodium intake; specific diuretics
Relationship between what can be greatly affect by potassium intake?
Relationship between tubular flow rate and potassium secretion
The higher the intake the ________ the effect created by tubular flow.
greater
As potassium diffuses into the tubular lumen, what happens to the gradient?
increase in luminal concentration; decreases the gradient thus decreasing the movement of potassium
Increase tubular flow does what to the gradient? Why?
Carries potassium away thus helping to preserve the gradient
The higher the flow, what happens to the gradient? So what gets secreted?
Better the gradient is preserved; the more potassium is secreted
With a high Na+ intake, aldosterone secretion ____________ (increases/decreases).
Decreases; which will produce a decrease in K+ secretion (but gets offset)
Aldosterone decreases, decreased sodium reabsorption, overall distal tubular flow is _____________(increased/decreased).
Increase; which results in an increase K+ secretion (but gets offset)
Acidosis (increased H+) ____________(increases/reduces) potassium secretion.
Reduces
Why does acidosis reduce potassium secretion?
Acidosis reduces Na-K ATPase activity; decreases driving force for moving potassium from cell interior to tubular lumen
Prolonged acidosis produces what? Why
Increased potassium secretion; result of decreased reabsorption of sodium chloride and water in proximal tubule and increased distal tubular flow
Alkalosis (decreased H+) __________(Increases/ decreases) potassium secretion.
Increases
What is the total calcium in plasma?
5 mEq/L
What percent of calcium is in ionized form? What percent is bound to plasma protein? What percent bound in non-ionized form to other ions?
50% ionized form
40% bound to plasma protein
10% non-ionized bound to phosphate,citrate
When does amount of calcium bound to protein decrease?
Increase in [H+]
Patients with alkalosis are more susceptible to what?
Hypocalcemic tetany
Hypocalcemic tetany
Hypocalcemia; increases muscle and nerve excitability
Hypercalcemia
depressed neuromuscular excitability which can lead to cardiac arrythmias
What percent of calcium is stored in bone?
99%; huge reservoir
If plasma concentration of calcium drops, body will do what with calcium?
Move from the bone
if plasma concentration rises, body will do what with calcium?
Move calcium back into the bone
What percent of calcium is present in intracellular space and cell organelles?
1%
What percent of calcium is present in extracellular fluid?
0.01%
What is the most important control agent for calcium?
Parathyroid hormone (PTH)
What percent of PTH is excreted via GI (feces)
90%; 900 mg/day
WHat percent of PTH is excreted via kidneys (urine)?
10% 100mg/day
PTH regulation accomplished by what three actions?
- Stimulation of bone resporption of calcium
- Stimulation of Vitamin D(3) which stimulates calcium reabsorption by intestines
- Direct stimulation of renal tubule reabsoprtion of calcium
As extracellular calcium concentration falls, what two things happen?
- Increased PTH
- Increased PTH concentration stimulates bone to increase release of bone salts which includes the release of large amounts of calcium
Resporption
release of bone salts
What two things happen as extracellular calcium concentration rises?
- Decreased PTH
2. Decreased PTH concentration decreases salt resporption to point where calcium will be added to the bone
How is calcium filtered?
Freely filtered
Does calcium get reabsorbed?
Yes
Does calcium get secreted?
No
How much of calcium present in the body are we filtering?
Very small percentage
What percent of calcium filtered load is reabsorbed in the proximal tubule?
65%
What percent of calcium filtered load is reasborbed in the proximal tubule?
25-30%
What percent of calcium filtered load is reabsorbed in the distal tubule/collecting tubule?
4-9 % filtered load
What percent of calcium filtered load is actually excreted?
1%; but changes as plasma concentration changes (intake changes)
What percent of calcium absorbed in the proximal tubule is carried by water via paracellular pathway?
80%
What percent of calcium absorbed in the proximal tubule is via transcellular pathway?
20%
Diffusion of calcium through luminal membrane into cell driven by what?
Chemical gradient (higher [Ca++] in lumen that inside cell) and electrical gradient
how is calcium pumped out of the cell?
Across basolateral border
Ca ATPase pump/ Na/Ca counter-transport
The paracellular pathway accounts for what percent of calcium reabsorption in the loop?
50%
Calcium undergoes passive diffusion down what type of gradient in the loop?
Electrical gradient; lumen has slight positive charge compared to interstitial fluid
Transcellular pathway accounts for what percent of calcium reabsorption in the lop?
50%; active process
Active process of transcellular pathway reabsorption of Ca++ in thick ascending loop stimulated by what?
PTH (most important), Vitamin D (calcitrol), calcitonin
What type of transport occurs in Ca++ reabsorption in the distal tubule?
Almost all transport by transcellular pathway; active transport across basolateral membrane; diffusion into cell
Increased PTH ___________(increases/decreases) Ca++ reabsorption in the distal tubule. What else increases calcium reabsoprtion?
Increases; increased by Vitamin D and calcitonin
Where does PTH have no effect on calcium reabsopriton?
Proximal tubule
What ion concentration affects [PTH]?
[Phosphate]; as [Phosphate] increases [PTH] increases
What ion concentration has major affect on transport mechanisms in the Distal tubule of calcium?
[H+]
What is the normal tubular max of phosphate?
0.1 mMol/min
If filtered load is under Tmax, how much of phosphate is reabsorbed?
All
If filtered load is over Tmax, how much of phosphate is reabsorbed?
Phosphate is actually exctreted
What is the plasma threshold for phosphate?
0.8 mMol/L
What is the normal plasma concentartion of phosphate?
1 mMol/L; large intake of phosphate each day (milk and meat)
In the proximal tubule, what percent of phosphate is reabsorbed?
75-80% of filtered phosphate is reabsorbed
What is the distal tubule, what percent of phosphate is reabsorbed?
10%
Ine the collecting duct, what percent of phosphate is reabsorbed?
very small amounts
What percent of phosphate is excrted?
10%
Phosphate Tmax changes based on what?
Intake. Low intake, Tmax will increase over time
What two things regulate phosphate?
Tmax and PTH
As PTH increases bone resorption of calcium, what else is resorbed?
phosphate
Increased PTH _________(increases/decreases) T max for phosphate so less phosphate is reabsorbed and more is excreted.
decreases
What percent of magnesium is stored in bone?
> 50%
Where is most of the magnesium that is not stored in bone?
Intracellular volume
What percent of magnesium is in extracellular volume?
<1%
What is the total plasma magnesium?
1.8 mEq/L
What percent of magnesium is bound to plasma proteins?
> 50%
Free ionized magnesium is what concentration
0.8 mEq/L
What is the daily intake of magnesium? What percent is absorbed byGI?
250-300 mg/day; but 50% is absorbed by GI (125-150 mg/day)
What is the amount of magnesium that the kidneys much excrete each day?
Total amount absorbed
Renal excretion of magnesium is
10 to 15 of filtered load
Magnesium reabsorption is what percent in the proximal tubule?
25%
Magnesium reabsorption what percent in the loop of henle?
65%
Magnesium reabsorption is what percent in distal tubule/collecting duct?
<5%
Increased magnesium = _________ reabsorption = _____________excretion.
Decreased, increased
Increased magnesium EC fluid volume results in ____________ reabsorption and ___________ excretion.
decreased, increased
increased calcium results in _______________ reabsorption and __________ excretion.
decreased, increased
