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Physio II > Control of K, Ca, PO3, Mg- Exam 4 > Flashcards

Control of K, Ca, PO3, Mg- Exam 4 Flashcards

1
Q

Potassium is tightly controlled. Usually changes less that what concentration?

A

+/- 0.3 mEq/L

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2
Q

Cell functions are very sensitive to changes in concentration of what ion?

A

Potassium; resting membrane potentials

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3
Q

What percent of potassium is located in the intracellular volume?

A

98%

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4
Q

What percent of potassium is located in the extracellular volume?

A

2%

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5
Q

What is the daily intake of potassium?

A

50 mEq/L - 200 mEq/L

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6
Q

Small changes in extracellular K+ can easily lead to what?

A

Hyper or hypokalemia

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7
Q

What percent of potassium intake is removed by feces?

A

5-10%

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8
Q

Potassium not removed by the feces must be removed how?

A

Kidneys

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9
Q

What is the first line of defense against changes in extracellular concentration of potassium?

A

Movement between intra and extracellular compartments possible

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10
Q

After ingesting 40 mEq of K+ into ECF, [K+] would increased by how much?

A

2.8 mEq/L

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11
Q

Most ingested K+ quickly moves where?

A

Into the cellular volume

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12
Q

What moves potassium and glucose into the cells following a meal?

A

Insulin

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13
Q

Increased [K+] stimulates secretion of what?

A

Aldosterone

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14
Q

What could affect ability to move K+ into the cells and K+ reabsorption?

A

Disease state

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15
Q

What stimulates B2-adrenergic receptors?

A

Epinephrine

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16
Q

What happens when epinephrine stimulates B2-adrenergic receptors?

A

Increasing movement of K+ into the cell.

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17
Q

What receptors do hypertension tx’s block?

A

B2- adrenergic blocking agents

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18
Q

B2-adrenergic blocking agents can lead to what condition?

A

Hyperkalemia

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19
Q

What are some potential factors that shift K+ into the cells?

A

Insulin
Aldosterone (K+ secretion)
B-adrenergic stimulation
Alkalosis

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20
Q

What are some factors that shift K+ out of cells?

A 
Insulin deficiency (DM)
Aldosterone deficiency (Addision's Disease)
B-adrenergic blockade
Acidosis
Cell lysis
Strenuous exercise
Increased extracellular fluid osmolarity
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21
Q

Increased [H+] will reduce the action of what pump? What does this result in?

A

Na-K ATPase; less transfer of K+ into the cells

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22
Q

What does cell lysis result in?

A

Dumps intracellular K+ in extracellular compartment

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23
Q

An increase in extracellular osmolarity, ________ moves out of the cell, increasing intracellular [K+], which increases the rate of ________ diffusion out of the cell.

A

water, K+

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24
Q

What three things determine excretion rate?

A

Rate of potassium filtration
Rate of potassium reabsorption
Rate of potassium secretion

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25
Q

What is the fraction of filtered load reabsorbed in the proximal tubule and loop of Henle day to day?

A

Constant; does not change day-to-day

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26
Q

Calculate the filtration of potassium.

A

180L/day x 4.2 mEq/L = 756 mEq/day

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27
Q

What percent of potassium is reabsorbed in the proximal tubule?

A

65%

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28
Q

What percent of potassium is reabsorbed in the loop? Mainly what segment?

A

25-30%; thick ascending segment

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29
Q

Flexible reabsorption and secretion of potassium utilizing what cells? Where are these cells located?

A

Principle cells; distal tubule and cortical collecting tubule

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30
Q

What is the normal intake of K+? How is removed?

A

100 mEq/day; 8mEq removed in feces; 92mEq removed in kidneys

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31
Q

Proximal tubule removes what concentration of potassium? Leaving how much?

A

491 mEq; leaving 265 mEq

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32
Q

Loop removes what concentration of ptassium? leaving how much?

A

Loop removes 204 mEq leaving 61 mEq

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33
Q

Distal tubule and cortical collecting tubule must secrete how much potassium? What fraction of excreted potassium?

A

31mEq; 1/3 of excreted potassium

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34
Q

During high potassium intake, what part of the nephron increases potassium secretion?

A

Distal tubule and cortical collecting tubule; very strong mechanism (rate of potassium excretion can exceed amount of potassium being filtered)

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35
Q

During low potassium intake, what decreases?

A

Secretion; can decrease to a point where this is net reabsorption

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36
Q

During low potassium intake, excretion can fall to what percent of filtered potassium?

A

1% (756 mEq/day x 0.01 = 8 mEq/day)

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37
Q

What cells make up 90% of cells in late distal and cortical collecting tubule?

A

Principle cells

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38
Q

Secretion driven by what pump? where?

A

Na-K ATPase; basolateral border of cells; move K+ into cell setting up concentration gradient; drives diffusion from cell into tubular lumen

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39
Q

What membrane contains special channels for K+ diffusion?

A

Tubular membrane; usually provides high permeability for K+ movement out of the cell

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40
Q

What cells reabsorb potassium, especially during potassium depletion?

A

Intercalated Cells

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41
Q

Reabsorption of potassium by intercalated cells could be related to what pump?

A

H-K ATPase

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42
Q

Where is the H-K ATPase pump located?

A

Tubular membrane

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43
Q

Where does H-K ATPase pump H+?

A

From tubular cell into lumen (secretion)

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44
Q

Where does H-K ATPase pump K+?

A

Tubular lumen into cell (reabsorption)

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45
Q

Where does K+ diffuse?

A

From cell into interstitial space via basolateral membrane

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46
Q

When does H-K ATPase have a major effect?

A

Only during potassium depletion

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47
Q

What three factors control the rate of K+ secretion?

A

Activity of Na-K ATPase
Electrochemical gradient for K+ from blood into tubular lumen
Permeability of tubular membrane to K+

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48
Q

What stimulates potassium secretion?

A

Increased extracellular [K+]
Increased [aldosterone]
Increased tubular flow rate

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49
Q

What will decrease potassium secretion?

A

Increased [H+]

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50
Q

T/F: There is always a certain level of secretion even at normal [K+].

A

True

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51
Q

Increased [K+] stimulates action of what pump? Where is K+ moved?

A

Na-K ATPase; More K+ moved into cell from interstitial space which increased gradient from cell interior to tubular lumen

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52
Q

Increased [K+] in plasma stimulates release of what hormone?

A

Aldosterone

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53
Q

Increased aldosterone increases rate of what reabsoprtion? Where in the nephron?

A

Rate of sodium reabsorption; late distal tubule and collecting duct

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54
Q

Increased aldosterone increases activity of what pump?

A

Na-K ATPase; so increase in sodium reabsorption will also increase potassium secretion

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55
Q

Increased Aldosterone increases membrane permeability for what?

A

Potassium

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56
Q

What is an example of negative feedback control system?

A

Plasma Potassium & Aldosterone

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57
Q

Small change in [K+] produces huge change in what?

A

Aldosterone concentration

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58
Q

What is the normal aldosterone level?

A

6 nag/dL

59
Q

Anything that affects our ability to produce aldosterone will have a big effect on excretion of what?

A

Potassium

60
Q

High aldosterone (primary aldosteronism) leads to what?

A

Hypokalemia

61
Q

Low aldosterone (Addison’s disease) leads to what?

A

Hyperkalemia

62
Q

In an experiment with dogs, increased K+ intake with intact aldosterone feedback resulted in what change in intake resulting in hwat change in [K+]?

A

Big change in intake (x7 increase)

Small change [K+] (4.2 - 4.3 mEq/L)

63
Q

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+]?

A

Big change in intake (x7 increase)

Big change in [K+] (3.8 - 4.7 mEq/L)

64
Q

Increased flow where will increase potassium secretion?

A

Distal tubular flow

65
Q

Increased tubular flow can be caused by what?

A

Volume expansion; high sodium intake; specific diuretics

66
Q

Relationship between what can be greatly affect by potassium intake?

A

Relationship between tubular flow rate and potassium secretion

67
Q

The higher the intake the ________ the effect created by tubular flow.

A

greater

68
Q

As potassium diffuses into the tubular lumen, what happens to the gradient?

A

increase in luminal concentration; decreases the gradient thus decreasing the movement of potassium

69
Q

Increase tubular flow does what to the gradient? Why?

A

Carries potassium away thus helping to preserve the gradient

70
Q

The higher the flow, what happens to the gradient? So what gets secreted?

A

Better the gradient is preserved; the more potassium is secreted

71
Q

With a high Na+ intake, aldosterone secretion ____________ (increases/decreases).

A

Decreases; which will produce a decrease in K+ secretion (but gets offset)

72
Q

Aldosterone decreases, decreased sodium reabsorption, overall distal tubular flow is _____________(increased/decreased).

A

Increase; which results in an increase K+ secretion (but gets offset)

73
Q

Acidosis (increased H+) ____________(increases/reduces) potassium secretion.

A

Reduces

74
Q

Why does acidosis reduce potassium secretion?

A

Acidosis reduces Na-K ATPase activity; decreases driving force for moving potassium from cell interior to tubular lumen

75
Q

Prolonged acidosis produces what? Why

A

Increased potassium secretion; result of decreased reabsorption of sodium chloride and water in proximal tubule and increased distal tubular flow

76
Q

Alkalosis (decreased H+) __________(Increases/ decreases) potassium secretion.

A

Increases

77
Q

What is the total calcium in plasma?

A

5 mEq/L

78
Q

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?

A

50% ionized form
40% bound to plasma protein
10% non-ionized bound to phosphate,citrate

79
Q

When does amount of calcium bound to protein decrease?

A

Increase in [H+]

80
Q

Patients with alkalosis are more susceptible to what?

A

Hypocalcemic tetany

81
Q

Hypocalcemic tetany

A

Hypocalcemia; increases muscle and nerve excitability

82
Q

Hypercalcemia

A

depressed neuromuscular excitability which can lead to cardiac arrythmias

83
Q

What percent of calcium is stored in bone?

A

99%; huge reservoir

84
Q

If plasma concentration of calcium drops, body will do what with calcium?

A

Move from the bone

85
Q

if plasma concentration rises, body will do what with calcium?

A

Move calcium back into the bone

86
Q

What percent of calcium is present in intracellular space and cell organelles?

A

1%

87
Q

What percent of calcium is present in extracellular fluid?

A

0.01%

88
Q

What is the most important control agent for calcium?

A

Parathyroid hormone (PTH)

89
Q

What percent of PTH is excreted via GI (feces)

A

90%; 900 mg/day

90
Q

WHat percent of PTH is excreted via kidneys (urine)?

A

10% 100mg/day

91
Q

PTH regulation accomplished by what three actions?

A
  1. Stimulation of bone resporption of calcium
  2. Stimulation of Vitamin D(3) which stimulates calcium reabsorption by intestines
  3. Direct stimulation of renal tubule reabsoprtion of calcium
92
Q

As extracellular calcium concentration falls, what two things happen?

A
  1. Increased PTH
  2. Increased PTH concentration stimulates bone to increase release of bone salts which includes the release of large amounts of calcium
93
Q

Resporption

A

release of bone salts

94
Q

What two things happen as extracellular calcium concentration rises?

A
  1. Decreased PTH

2. Decreased PTH concentration decreases salt resporption to point where calcium will be added to the bone

95
Q

How is calcium filtered?

A

Freely filtered

96
Q

Does calcium get reabsorbed?

A

Yes

97
Q

Does calcium get secreted?

A

No

98
Q

How much of calcium present in the body are we filtering?

A

Very small percentage

99
Q

What percent of calcium filtered load is reabsorbed in the proximal tubule?

A

65%

100
Q

What percent of calcium filtered load is reasborbed in the proximal tubule?

A

25-30%

101
Q

What percent of calcium filtered load is reabsorbed in the distal tubule/collecting tubule?

A

4-9 % filtered load

102
Q

What percent of calcium filtered load is actually excreted?

A

1%; but changes as plasma concentration changes (intake changes)

103
Q

What percent of calcium absorbed in the proximal tubule is carried by water via paracellular pathway?

A

80%

104
Q

What percent of calcium absorbed in the proximal tubule is via transcellular pathway?

A

20%

105
Q

Diffusion of calcium through luminal membrane into cell driven by what?

A

Chemical gradient (higher [Ca++] in lumen that inside cell) and electrical gradient

106
Q

how is calcium pumped out of the cell?

A

Across basolateral border

Ca ATPase pump/ Na/Ca counter-transport

107
Q

The paracellular pathway accounts for what percent of calcium reabsorption in the loop?

A

50%

108
Q

Calcium undergoes passive diffusion down what type of gradient in the loop?

A

Electrical gradient; lumen has slight positive charge compared to interstitial fluid

109
Q

Transcellular pathway accounts for what percent of calcium reabsorption in the lop?

A

50%; active process

110
Q

Active process of transcellular pathway reabsorption of Ca++ in thick ascending loop stimulated by what?

A

PTH (most important), Vitamin D (calcitrol), calcitonin

111
Q

What type of transport occurs in Ca++ reabsorption in the distal tubule?

A

Almost all transport by transcellular pathway; active transport across basolateral membrane; diffusion into cell

112
Q

Increased PTH ___________(increases/decreases) Ca++ reabsorption in the distal tubule. What else increases calcium reabsoprtion?

A

Increases; increased by Vitamin D and calcitonin

113
Q

Where does PTH have no effect on calcium reabsopriton?

A

Proximal tubule

114
Q

What ion concentration affects [PTH]?

A

[Phosphate]; as [Phosphate] increases [PTH] increases

115
Q

What ion concentration has major affect on transport mechanisms in the Distal tubule of calcium?

A

[H+]

116
Q

What is the normal tubular max of phosphate?

A

0.1 mMol/min

117
Q

If filtered load is under Tmax, how much of phosphate is reabsorbed?

A

All

118
Q

If filtered load is over Tmax, how much of phosphate is reabsorbed?

A

Phosphate is actually exctreted

119
Q

What is the plasma threshold for phosphate?

A

0.8 mMol/L

120
Q

What is the normal plasma concentartion of phosphate?

A

1 mMol/L; large intake of phosphate each day (milk and meat)

121
Q

In the proximal tubule, what percent of phosphate is reabsorbed?

A

75-80% of filtered phosphate is reabsorbed

122
Q

What is the distal tubule, what percent of phosphate is reabsorbed?

A

10%

123
Q

Ine the collecting duct, what percent of phosphate is reabsorbed?

A

very small amounts

124
Q

What percent of phosphate is excrted?

A

10%

125
Q

Phosphate Tmax changes based on what?

A

Intake. Low intake, Tmax will increase over time

126
Q

What two things regulate phosphate?

A

Tmax and PTH

127
Q

As PTH increases bone resorption of calcium, what else is resorbed?

A

phosphate

128
Q

Increased PTH _________(increases/decreases) T max for phosphate so less phosphate is reabsorbed and more is excreted.

A

decreases

129
Q

What percent of magnesium is stored in bone?

A

> 50%

130
Q

Where is most of the magnesium that is not stored in bone?

A

Intracellular volume

131
Q

What percent of magnesium is in extracellular volume?

A

<1%

132
Q

What is the total plasma magnesium?

A

1.8 mEq/L

133
Q

What percent of magnesium is bound to plasma proteins?

A

> 50%

134
Q

Free ionized magnesium is what concentration

A

0.8 mEq/L

135
Q

What is the daily intake of magnesium? What percent is absorbed byGI?

A

250-300 mg/day; but 50% is absorbed by GI (125-150 mg/day)

136
Q

What is the amount of magnesium that the kidneys much excrete each day?

A

Total amount absorbed

137
Q

Renal excretion of magnesium is

A

10 to 15 of filtered load

138
Q

Magnesium reabsorption is what percent in the proximal tubule?

A

25%

139
Q

Magnesium reabsorption what percent in the loop of henle?

A

65%

140
Q

Magnesium reabsorption is what percent in distal tubule/collecting duct?

A

<5%

141
Q

Increased magnesium = _________ reabsorption = _____________excretion.

A

Decreased, increased

142
Q

Increased magnesium EC fluid volume results in ____________ reabsorption and ___________ excretion.

A

decreased, increased

143
Q

increased calcium results in _______________ reabsorption and __________ excretion.

A

decreased, increased

Physio II (14 decks)

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