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Pierce - Regulation Of Ca/Pi/Mg Flashcards

1
Q

What percent of Ca2+ is in BONE, ICF, and ECF?

A 
Bone = 99%
ICF = 1%
ECF = 0.1%
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2
Q

What is the total plasma level of Ca2+?

A

5.0 mEq/L

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3
Q

How much Ca2+ is excreted through feces?

A

90%

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4
Q

What % of Ca2+ is protein-bound? Does it filter across the glomerulus?

A

40% and NO!

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5
Q

Which 2 components constitute filterable Ca2+ at the glomerulus? What % of Ca2+ is filtered?

A

Ionized Ca2+ (45%)
Diffusible Ca2+ Complexes (15%)
Total = 60%

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6
Q

What effect does HYPOalbuminemia have on IONIZED (i.e. Free) plasma Ca2+?

A

INCREASES plasma Ca2+

H+ competes with Ca2+ for albumin binding sites (but it usually wins.)

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7
Q

What effect does HYPERalbuminemia have on IONIZED (i.e. Free) plasma Ca2+?

A

DECREASES Plasma Ca2+

Both H+ and Ca2+ have enough binding sites

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8
Q

If albumin levels are constant, what occurs to plasma Ca2+ in an ACIDOTIC state? ALKALOTIC state?

A

Acidotic State - More FREE Ca2+

Alkalotic State - More Ca2+ BOUND to proteins

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9
Q

Which condition are individuals predisposed to with ALKALOSIS?

A

Hypocalcemic Tetany

DECREASED extracellular Ca2+ doesn’t inhibit the Na+ channels as much, so they will depolarize easier — create tetany.

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10
Q

What is the “net effect” of Calcitriol?

A

INCREASE Serum Ca2+ and Pi

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11
Q

What is the effect of Calcitriol on BONE?

A

Promotoes osteoclastic mediated bone RESORPTION (breakdown) — works synergistically with PTH.

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12
Q

What is the effect of Calcitriol on the INTESTINE?

A

INCREASES Ca2+ (30% dietary Ca2+ absorbed) and Pi ABSORPTION

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13
Q

What is the effect of Calcitriol on the KIDNEY?

A

INCREASES Ca2+ and Pi REABSORTION

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14
Q

What is the “net effect” of Calcitonin?

A

DECREASES serum Ca2+ and Pi concentrations

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15
Q

What is the effect of Calcitonin on BONE?

A

INHIBITS osteoclastic mediated bone resorption — DECREASES activity/number of osteoclasts.

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16
Q

What is the effect of CALCITONIN on the KIDNEY?

A

PROMOTE Ca2+ and Pi EXCRETION

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17
Q

What is the “net effect” of Parathyroid Hormone (PTH)?

A

INCREASE Serum Ca2+

DECREASE Serum Pi

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18
Q

What is the effect of PTH on BONE?

A

INCREASES osteoclastic RESORPTION (Breakdown) — works with Calcitriol.

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19
Q

What is the effect of PTH on INTESTINE?

A

INCREASES Ca2+/Pi absorption INDIRECTLY via Vitamin D (Calcitriol) production

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20
Q

What is the effect of PTH on the KIDNEY?

A

INCREASE reabsorption Ca2+ in DCT

DECREASE reabsorption Pi in PCT
DECREASE Na+/H+ Antiporter
DECREASE HCO3- Reabsorption

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21
Q

What is the function and location of CaSR?

A

ONLY THICK ASCENDING LIMB

Monitor Ca2+ levels; Inhibit apical membrane Ca2+ reabsorption when [Ca2+] plasma HIGH.

Blocks NKCC2 and ROMK transporters —> Disrupts luminal positive potential gradient —> Ca2+ has no driving force to move —> Ca2+ reabsorption INHIBITED

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22
Q

What is the formula for calculating Ca2+ FILTERED LOAD?

A

Filtered Load = (GFR)(Plasma Conc.)(% Filterability)

With Ca2+, % Filterability = 60%

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24
Q

By which method is Ca2+ REABSORBED in the Proximal Tubule?

A

Primarily PARACELLULAR

Some TRANSCELLULAR

  • Diffusion down gradient into cell
  • Exits cell via Ca2+ ATPase and Na+/Ca2+ EXCHANGER
25
Q

How does ECF Volume Contraction effect Ca2+ REABSORPTION in the Proximal Tubule?

A

Ca2+ reabsorption INCREASES

ECF Vol. Contraction —> DECREASED arterial press. —> RAAS activated —> Ang. II stimulates Na+/H+ EXCHANGER —> INCREASE Na+ REABSORPTION —> Parallel INCREASE Ca2+ REABSORPTION

26
What percent of Ca2+ is REABSORBED in the Proximal Tubule?
65-70% filtered Ca2+ REABSORBED
27
How does ECF Volume Expansion effect Ca2+ REABSORPTION in the Proximal Tubule?
Ca2+ reabsorption DECREASES ECF Vol. Expansion —> DECREASED Peritubular Oncotic pressure —> DECREASED fractional reabsorption isosmotic fluid —> DECREASED Na+ REABSORPTION —> Parallel DECREASED Ca2+ REABSORPTION
28
What percentage of Ca2+ is REABSORBED in the Thick Ascending Limb (TAL)?
25%
29
What drives the paracellular movement of Ca2+ from the lumen into the interstitum?
TEPD (Transepithelial Potential Difference) - Lumen POSITIVE potential difference drives the Ca2+ from the lumen into the interstitum.
30
What establishes the positive TEPD in the TAL?
Recycling of K+ into the lumen establishes the NKCC Cotransporter as ELECTROGENIC —> brings in more negative than positive charge into cell.
31
What is the primary method for Ca2+ reabsorption in the TAL?
Paracellular —> Again, it is coupled with Na+ reabsorption | Na+ reabsorption in TAL is LOAD DEPENDENT
32
What effect does ADH have on Ca2+ REABSORPTION in the TAL?
ADH stimulates Ca2+ reabsorption Increase ADH —> Increase Na+/Cl- REABSORPTION in TAL —> Concomitant Increase in Ca2+ REABSORPTION
33
What effect do Loop Diuretics (i.e. Furosemide) have on Ca2+ REABSORPTION?
Loop Diuretics INHIBIT NKCC Cotransporter —> Lumen positive potential diminished —> Elimination of paracellular driving force for Ca2+ REABSORPTION Loop Diuretics TREAT HYPERCALCEMIA
34
Which portion of the nephron is the MAJOR SITE of Ca2+ regulation?
Distal Tubule
35
What percentage of Ca2+ is REABSORBED in the Distal Tubule?
Approximately 8%
36
In the Distal Tubule, how does Ca2+ cross from the Tubular Lumen to the Intersitial Fluid?
1. Crosses APICAL via TRPV5 | 2. Crosses BASOLATERAL via Na+/Ca2+ EXCHANGER (NCE)
37
What is the TEPD in the Distal Tubule? How does this effect Ca2+ transport?
TEPD - Lumen-negative transepithelial voltage requires ACTIVE transcellular transport for Ca2+ REABSORPTION
38
What effects do PTH and Calcitriol have on Ca2+ REABSORPTION in the Distal Tubule?
STIMULATE REABSORPTION via the basolateral receptor — Hypocalciuric Action of PTH.
39
What effect do Thiazide Diuretics have on Na+ and Ca2+ REABSORPTION in the Distal Tubule?
INHIBIT Na+ REABSORPTION STIMULATE Ca2+ REABSORPTION - Treatment for Ca2+ containing Kidney Stones
40
What effect does ACIDEMIA have on Ca2+ EXCRETION? What is the mechanism of action?
INCREASES Ca2+ EXCRETION via INHIBITION of APICAL TRPV5 Transporter.
41
What effect does ALKALEMIA have on Ca2+ EXCRETION? What is the mechanism of action?
DECREASES Ca2+ EXCRETION by STIMULATION of apical transporter TRPV5
42
What is the equation for Filtered Load of Phosphate (Pi)?
Filtered Load = (GFR)(Plasma Con.)(% Filterability)
43
What percentage of Pi is REABSORBED by the Proximal Tubule?
80% REABSORBED by Proximal Tubule
44
How is Pi REABSORBED across the APICAL membrane? BASOLATERAL membrane?
APICAL - Na+/Pi COTRANSPORTER BASOLATERAL - Unknown
45
How is Na+ REABSORBED across the APICAL membrane in the EARLY Proximal Tubule?
``` Symporters: Na+ / Glucose Na+ / Amino Acid Na+ / Pi Na+ / HCO3- ``` Antiporters: Na+ / H+ Na+ / Organic Solutes
46
What DRIVES the REABSORPTION of Na+/Pi?
Na+ / K+ ATPase on the BASOLATERAL Membrane
47
Where is Calcitriol produced in the kidneys?
Proximal Tubule Epithelial Cells
48
Which enzyme converts the INACTIVE Calcitriol —> ACTIVE Calcitriol?
Renal 1 alpha-hydroxylase
49
What UPREGULATES Renal 1 alpha-Hydroxylase? DOWNREGULATES?
Upregulates: Low Ca2+ Low Pi High PTH Downregulates: High Ca2+ (via CaSR)
50
What effect does FGF-23 have on Pi?
PTH, Calcitriol, and Hyperphoshetemia signal bone to secrete FGF-23 —> INHIBITS Pi REABSORPTION in the Proximal Tubule —> INCREASES Pi EXCRETION
51
What effect does PTH have on Pi?
Inhibits Na+/H+ EXCHANGER andNa+/Pi COTRANSPORT —> Inhibits Pi REABSORPTION —> INCREASED Pi Renal Excretion (Phosphaturia) and DECREASED Serum Pi
52
What effect does Calcitriol have on Pi?
INCREASES Serum Pi by increasing intestinal phosphate absorption
53
What percentage of Mg2+ is REABSORBED in the Proximal Tubule? By what mechanism?
20% REABSORBED Paracellular —> follow Na+ and H20
54
What percentage of Mg2+ is REABSORBED in the Thick Ascending Limb?
70% REABSORBED
55
What mechanism drives the REABSORPTION of Mg2+ in the Thick Ascending Limb?
Paracellular Driven by the Lumen Positive Potential Difference (TEPD) of TAL Note: Loop Diuretics inhibit Mg2+ reabsorption
56
What percentage of Mg2+ is REABSORPED in the Distal Tubule?
10% Reabsorped Concentration same inside/outside cell, so driving force is electrical potential.
57
How does Mg2+ cross the APICAL membrane in the Distal Tubule?
TRPM6 Intracellular and Basolateral shuttling not clearly understood.

Renal Final (3 decks)

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