TOPIC 11 Control of K, Ca, Phosphate and Mg Flashcards
Total calcium in plasma: mEq/liter
Total calcium in plasma: 5 mEq/liter
Total calcium in plasma: % distribution ionized, non-ionized and bound ?
50% in ionized form
40% bound to plasma protein
Amount bound to protein decreases with an increase in [H+]. Patients with alkalosis more susceptible to hypocalcemic tetany
10% bound in non-ionized form to other ions (phosphate, citrate)
Amount of Ca bound to protein decreases with an increase in what ion?
what patients are more susceptible to this?
[H+]. Patients with alkalosis more susceptible to hypocalcemic tetany
Ca Normal ion concentration: mEq/liter
2.4 mEq/liter (1.2 mmol/liter)
Hypocalcemia:
increases muscle and nerve excitability (hypocalcemic tetany)
Hypercalcemia
depressed neuromuscular excitability which
can lead to cardiac arrhythmias
99% of calcium stored where?
bone
HUGE reservoir–if plasma concentration drops, body will move calcium from the bone
–if plasma concentration rises, body will move calcium back into the bone
% Ca present in intracellular space and cell organelles
1%
% Ca present in extracellular fluid
0.01%
Parathyroid Hormone As with all ions, intake and output must be matched over time, with output changing to match match what?
to match the input
PTH most important control agent for what?
calcium
How is Parathyroid Hormone excreted?
90% excreted via gastrointestinal tract (feces) (≈900 mg/day)
10% excreted via kidneys (urine) (≈100 mg/day)
PTH regulation accomplished through 3 actions: (stimulations)
Stimulation of bone resporption of calcium
Stimulation of vitamin D which stimulates calcium reabsorption by intestines
Direct stimulation of renal tubule reabsorption of calcium
As extracellular calcium concentration falls: what is the parathyroid gland stimulated to do?
which does what?
(this is in regard to the bones)
Parathyroid gland directly stimulated to increase secretion of PTH
Increased PTH concentration stimulates bone to increase release of bone salts (resporption) which includes the release of large amounts of calcium
As extracellular calcium concentration increases: what does the parathyroid gland do? which does what?
(this is in regard to the bones)
Parathyroid gland decreases PTH secretion
Decreased PTH concentration decreases salt
resporption to point where calcium will be added to the bone
Difference between resp acidosis
increasing Volume of H+ with an end production of CO2
When will we see phosphate in our urine?
if we have a higher than normal concentration and it exceeds our ability to reabsorb (Tmax
Ca excretion rate ?
how much of body’s Ca are we actually filtering ?
Freely filtered, reabsorbed BUT NOT secreted
Excretion rate = Filtration–Reabsorption
Only filtering a very small percentage of the calcium that is actually present in the body!!!!!
% Ca filtered load reabsorbed in the proximal tubule:
65% filtered load reabsorbed
% Ca filtered load reabsorbed in the LOH?
25 to 30% filtered load reabsorbed
% Ca filtered load reabsorbed in Distal tubule / Collecting tubule
4 to 9% filtered load reabsorbed
% of Ca filtered load normally excreted?
Normally only 1% is excreted
Changes as plasma concentration changes (i.e. intake changes)
Ca reabsorbed in the proximal tubule % carried via paracellular pathway and transcellular pathway ?
80% of amount reabsorbed carried by water via paracellular pathway
20% of amount reabsorbed via a transcellular pathway
Ca reabsorbed via transcellular pathway works how? diffusion driven by what? and pumped out via what?
In Proximal Tubule
Diffusion through luminal membrane into cell driven by chemical gradient (higher [Ca++] in lumen than inside cell) AND by electrical gradient (interior of cell negative with respect to lumen
Pumped out of cell across basolateral membrane via Ca ATPase pump and Na-Ca counter-transport mechanism
Ca % of reabsorption by paracellular pathway ?
In Thick Ascending Loop of Henle
Paracellular pathway accounts for 50% of reabsorption in loop
Transcellular pathway accounts for 50% of reabsorption in loop
Ca reabsorbed by paracellular pathway — via how?
In Thick Ascending Loop of Henle
Passive diffusion down electrical gradient–lumen has slight positive charge compared to interstitial fluid
Ca reabsorbed by Transcellular pathway – what process?
In Thick Ascending Loop of Henle
Active process stimulated by PTH, Vitamin D (Calcitrol), and calcitonin (PTH concentration most important)
In the Distal Tubulal - Ca Reabsorption is transported almost all via what pathway? and what type of transport is it?
Almost all transport via Transcellular pathway
Active transport across basolateral membrane –diffusion into cell
Increased [PTH] increases Ca ++ reabsorption
Reabsorption also increased by Vitamin D and calcitonin
In the Distal Tubulal - increased PTH does what to Ca++?
Increased [PTH] increases Ca++reabsorption
Reabsorption also increased by Vitamin D and calcitonin
PTH is a Primary controller of what?
Regulation of Ca++Reabsorption / Excretion
INCREASED Ca reabsorption means there is an increase in what 2 other things too?
From an ⬆️ PTH and there is an increase with that Plasma Phosphate
Vit D3
INCREASED Ca reabsorption caused by a decrease in what?
Caused by a ⬇️ BP and ECFV
INCREASED Ca reabsorption caused by what kind of acid base status ?
Metabolic Acidosis
Decreased Ca reabsorption caused by increase in what 2 things ?
⬆️ BP and ECFV
Decreased Ca reabsorption caused by a decrease in what?
⬇️ PTH and goes along decrease Plasma Phosphate
Decreased Ca reabsorption caused what kind of acid base status ?
Metabolic Alkalosis
PTH has no effect in what Tubule
(Following sodium and water
reabsorption)
in Proximal Tubule
Following sodium and water reabsorption
[Phosphate] affects [PTH]–As [Phosphate] increases, [PTH] does what?
increases
[H+] major affect is on the transport
mechanisms in what Tubule?
Distal Tubule
If filtered load under Tmax, all phosphate is what?
all phosphate reabsorbed
If filtered load over Tmax, phosphate is what?
phosphate is excreted
Phosphate Plasma threshold level is approx? mMol/L
Phosphate Normal plasma concentration around mMol/liter?
-0.8 mMol/liter
-1 mMol/liter
–Large intake of phosphate each day (milk & meat)
Proximal Tubule: % of of filtered phosphate reabsorbed
75 to 80%
Enters cells from lumen via Na
-Phosphate co-transport mechanism
Leaves cell via counter-transport mechanism across basolateral membrane
Phosphate reabsorbed into Proximal Tubule by what transport mechanism?
Phosphate co-transport mechanism
Leaves cell via counter-transport mechanism across basolateral membrane
Phosphate reabsorbed amount in LOH?
Loop of Henle: Very small amounts
Phosphate reabsorbed amount in Distal Tubule?
10% of filtered phosphate reabsorbed
Phosphate reabsorbed amount in Collecting Tubule?
Very small amounts
Approximately what % of filtered phosphate is excreted?
10%
Phosphate Tmax can change based on what?
intake
-Low intake, Tmax will increase over time
As PTH increases bone resorption of what two other substances are also reSORBED?
calcium & phosphate are also resorbed
Magnesium - where is it stored/located?
> 50% stored in bone
Most of what is left is located in the intracellular volume
<1% located in extracellular volume
Renal excretion of magnesium is ≈ what % of filtered load?
10 to 15% of filtered load
TOTAL plasma magnesium = 1.8 mEq/liter BUT what % is bound? making what new amount free?
> 50% is bound to plasma proteins so free ionized is 0.8 mEq/liter
What % of Mg is absorbed in the GI tract?
only 50% is actually absorbed by the gastrointestinal tract
What % of filtered load of Mg is reabsorbed in the Proximal Tubule?
Proximal Tubule: 25% of filtered load
What % of filtered load of Mg is reabsorbed in the Loop of Henle?
Primary site of reabsorption–65% of filtered load
What % of filtered load of Mg is reabsorbed in the Distal Tubule / Collecting Tubule?
<5% of filtered load
⬆️ [Magnesium] results in what to reabsorption and excretion?
⬇️ reabsorption and ⬆️ excretion
⬆️ EC fluid volume results in what to reabsorption and excretion?
⬇️ reabsorption and ⬆️ excretion
⬆️ [Ca++] results in what to reabsorption and excretion?
⬇️ reabsorption and ⬆️ excretion
K levels fluctuations?
Tightly controlled
–Usually changes less than ± 0.3 mEq/liter
K amount %’s in intracellular & extracellular spaces?
98% located intracellular volume
–only 2% extracellular
K first line of defense against changes in
extracellular concentration?
Movement between intra and
extracellular compartments possible
K elimination how?
Only 5 to 10% of intake removed by feces
–rest must be removed by kidneys
Insulin moves what 2 things into the cells following a meal?
potassium AND glucose
Factors that shifts K+ into cells (Potential hypo) (4)
Insulin
Aldosterone (also increase K secretion)
Alkalosis
Β-adrenergic stimulation
Factors that shifts K+ out of cells (Potential hyper) (7)
Insulin deficiency Aldosterone deficiency Acidosis B-adrenergic blockade Cell lysis Strenuous exercise Increased extracellular fluid osmolarity
Epinephrine stimulates β2-adrenergic receptors increasing movement of K+ where?
into the cell.
β2-adrenergic blocking agents treats what? and can lead to what?
hypertension) can lead to hyperkalemia
Increased [H+] will reduce action of Na-K ATPase with less transfer of what into the cells?
K+ into the cells
With an increase in extracellular K osmolarity, water moves out of the cell increasing _____ [K+] which increases the rate of K+ diffusion ______
intracellular
out of the cell
Consistent Reabsorption of K % in proximal tubule?
65%
Consistent Reabsorption of K % loop (mainly thick ascending segment)?
25 to 30%
With normal K+ intake of 100 mEq/day what would feces and kidneys remove?
Feces removes 8 mEq
Kidneys must remove 92 mEq
High potassium intake
Distal tubule & cortical collecting tubule
increase potassium what?
increase potassium secretion
Very strong mechanism–rate of potassium excretion can exceed amount of potassium being filtered
Low potassium intake – Secretion rate does what?
decreases
Can decrease secretion to point where there is net reabsorption
Excretion can fall to 1% of filtered potassium (756 mEq/day x 0.01 = 8mEq/day)
Principal Cells
Make up what % of cells in late distal and cortical collecting tubule?
90%
Intercalated Cells Reabsorb what?
In distal tubule and cortical collecting duct
Reabsorb potassium especially during potassium depletion
H-K ATPase
located where? and pumps what which ways?
All taking place in distal and cortical collecting duct
Located tubular membrane
Pumps H+ from tubular cell into lumen (secretion)
Pumps K+ from tubular lumen into cell (reabsorption)
K+ diffuses from cell into interstitial space via basolateral membrane
H-K ATPase major effect only during what depletion?
In distal and cortical collecting duct
Major effect only during potassium depletion
Increased [H+] will do what to potassium secretion?
In distal and cortical collecting ducts
DECREASE
Stimulation of Potassium Secretion by what 3 things?
In distal tubules and cortical collecting ducts
Increased extracellular [K+]
Increased [aldosterone]
Increased tubular flow rate
Increased aldosterone increases rate of sodium reabsorption by what parts of the nephron?
late distal tubule and collecting duct
[K+] of renal interstitial fluid increases (increased plasma concentration) which
decreases amount of K+ diffusing from cell interior _____
into interstitial space
Plasma Potassium & Aldosterone
Great example of _____ control system
negative feedback
Factor being controlled (potassium) as feedback effect on controller (aldosterone)
Small change in plasma [K+] produced __ change in aldosterone concentration
huge
Normal aldosterone level is approximately 6 nag/dL
Anything that affects our ability to produce aldosterone will have a big effect on ____ excretion!!
potassium
High aldosterone (primary aldosteronism) — ___kalemia
Hypokalemia
Low aldosterone (Addison’s disease)- ___kalemia
Hyperkalemia
Acidosis (___ H+) _____ potassium secretion
(INCREASED H+) reduces potassium secretion
Reduces the activity of Na-K ATPase–decreases driving force for moving potassium from cell interior to tubular lumen
Prolonged acidosis produces increased potassium excretion
–Result of decreased reabsorption of sodium
chloride and water in proximal tubule and increased distal tubular flow
Alkalosis (___ H+) _____ potassium secretion
( Decreases H+) increases potassium secretion
Increased distal tubular flow rate will ____ potassium secretion?
increase
Increased tubular flow rate can be caused by volume expansion; high sodium intake; specific diuretics
