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
2
Q
Cell functions are very sensitive to changes in concentration of what ion?
A
Potassium; resting membrane potentials
3
Q
What percent of potassium is located in the intracellular volume?
A
98%
4
Q
What percent of potassium is located in the extracellular volume?
A
2%
5
Q
What is the daily intake of potassium?
A
50 mEq/L - 200 mEq/L
6
Q
Small changes in extracellular K+ can easily lead to what?
A
Hyper or hypokalemia
7
Q
What percent of potassium intake is removed by feces?
A
5-10%
8
Q
Potassium not removed by the feces must be removed how?
A
Kidneys
9
Q
What is the first line of defense against changes in extracellular concentration of potassium?
A
Movement between intra and extracellular compartments possible
10
Q
After ingesting 40 mEq of K+ into ECF, [K+] would increased by how much?
A
2.8 mEq/L
11
Q
Most ingested K+ quickly moves where?
A
Into the cellular volume
12
Q
What moves potassium and glucose into the cells following a meal?
A
Insulin
13
Q
Increased [K+] stimulates secretion of what?
A
Aldosterone
14
Q
What could affect ability to move K+ into the cells and K+ reabsorption?
A
Disease state
15
Q
What stimulates B2-adrenergic receptors?
A
Epinephrine
16
Q
What happens when epinephrine stimulates B2-adrenergic receptors?
A
Increasing movement of K+ into the cell.
17
Q
What receptors do hypertension tx’s block?
A
B2- adrenergic blocking agents
18
Q
B2-adrenergic blocking agents can lead to what condition?
A
Hyperkalemia
19
Q
What are some potential factors that shift K+ into the cells?
A
Insulin
Aldosterone (K+ secretion)
B-adrenergic stimulation
Alkalosis
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
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
22
Q
What does cell lysis result in?
A
Dumps intracellular K+ in extracellular compartment
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+
24
Q
What three things determine excretion rate?
A
Rate of potassium filtration
Rate of potassium reabsorption
Rate of potassium secretion
25
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
26
Calculate the filtration of potassium.
180L/day x 4.2 mEq/L = 756 mEq/day
27
What percent of potassium is reabsorbed in the proximal tubule?
65%
28
What percent of potassium is reabsorbed in the loop? Mainly what segment?
25-30%; thick ascending segment
29
Flexible reabsorption and secretion of potassium utilizing what cells? Where are these cells located?
Principle cells; distal tubule and cortical collecting tubule
30
What is the normal intake of K+? How is removed?
100 mEq/day; 8mEq removed in feces; 92mEq removed in kidneys
31
Proximal tubule removes what concentration of potassium? Leaving how much?
491 mEq; leaving 265 mEq
32
Loop removes what concentration of ptassium? leaving how much?
Loop removes 204 mEq leaving 61 mEq
33
Distal tubule and cortical collecting tubule must secrete how much potassium? What fraction of excreted potassium?
31mEq; 1/3 of excreted potassium
34
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)
35
During low potassium intake, what decreases?
Secretion; can decrease to a point where this is net reabsorption
36
During low potassium intake, excretion can fall to what percent of filtered potassium?
1% (756 mEq/day x 0.01 = 8 mEq/day)
37
What cells make up 90% of cells in late distal and cortical collecting tubule?
Principle cells
38
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
39
What membrane contains special channels for K+ diffusion?
Tubular membrane; usually provides high permeability for K+ movement out of the cell
40
What cells reabsorb potassium, especially during potassium depletion?
Intercalated Cells
41
Reabsorption of potassium by intercalated cells could be related to what pump?
H-K ATPase
42
Where is the H-K ATPase pump located?
Tubular membrane
43
Where does H-K ATPase pump H+?
From tubular cell into lumen (secretion)
44
Where does H-K ATPase pump K+?
Tubular lumen into cell (reabsorption)
45
Where does K+ diffuse?
From cell into interstitial space via basolateral membrane
46
When does H-K ATPase have a major effect?
Only during potassium depletion
47
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+
48
What stimulates potassium secretion?
Increased extracellular [K+]
Increased [aldosterone]
Increased tubular flow rate
49
What will decrease potassium secretion?
Increased [H+]
50
T/F: There is always a certain level of secretion even at normal [K+].
True
51
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
52
Increased [K+] in plasma stimulates release of what hormone?
Aldosterone
53
Increased aldosterone increases rate of what reabsoprtion? Where in the nephron?
Rate of sodium reabsorption; late distal tubule and collecting duct
54
Increased aldosterone increases activity of what pump?
Na-K ATPase; so increase in sodium reabsorption will also increase potassium secretion
55
Increased Aldosterone increases membrane permeability for what?
Potassium
56
What is an example of negative feedback control system?
Plasma Potassium & Aldosterone
57
Small change in [K+] produces huge change in what?
Aldosterone concentration
58
What is the normal aldosterone level?
6 nag/dL
59
Anything that affects our ability to produce aldosterone will have a big effect on excretion of what?
Potassium
60
High aldosterone (primary aldosteronism) leads to what?
Hypokalemia
61
Low aldosterone (Addison's disease) leads to what?
Hyperkalemia
62
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)
63
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)
64
Increased flow where will increase potassium secretion?
Distal tubular flow
65
Increased tubular flow can be caused by what?
Volume expansion; high sodium intake; specific diuretics
66
Relationship between what can be greatly affect by potassium intake?
Relationship between tubular flow rate and potassium secretion
67
The higher the intake the ________ the effect created by tubular flow.
greater
68
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
69
Increase tubular flow does what to the gradient? Why?
Carries potassium away thus helping to preserve the gradient
70
The higher the flow, what happens to the gradient? So what gets secreted?
Better the gradient is preserved; the more potassium is secreted
71
With a high Na+ intake, aldosterone secretion ____________ (increases/decreases).
Decreases; which will produce a decrease in K+ secretion (but gets offset)
72
Aldosterone decreases, decreased sodium reabsorption, overall distal tubular flow is _____________(increased/decreased).
Increase; which results in an increase K+ secretion (but gets offset)
73
Acidosis (increased H+) ____________(increases/reduces) potassium secretion.
Reduces
74
Why does acidosis reduce potassium secretion?
Acidosis reduces Na-K ATPase activity; decreases driving force for moving potassium from cell interior to tubular lumen
75
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
76
Alkalosis (decreased H+) __________(Increases/ decreases) potassium secretion.
Increases
77
What is the total calcium in plasma?
5 mEq/L
78
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
79
When does amount of calcium bound to protein decrease?
Increase in [H+]
80
Patients with alkalosis are more susceptible to what?
Hypocalcemic tetany
81
Hypocalcemic tetany
Hypocalcemia; increases muscle and nerve excitability
82
Hypercalcemia
depressed neuromuscular excitability which can lead to cardiac arrythmias
83
What percent of calcium is stored in bone?
99%; huge reservoir
84
If plasma concentration of calcium drops, body will do what with calcium?
Move from the bone
85
if plasma concentration rises, body will do what with calcium?
Move calcium back into the bone
86
What percent of calcium is present in intracellular space and cell organelles?
1%
87
What percent of calcium is present in extracellular fluid?
0.01%
88
What is the most important control agent for calcium?
Parathyroid hormone (PTH)
89
What percent of PTH is excreted via GI (feces)
90%; 900 mg/day
90
WHat percent of PTH is excreted via kidneys (urine)?
10% 100mg/day
91
PTH regulation accomplished by what three actions?
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
As extracellular calcium concentration falls, what two things happen?
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
Resporption
release of bone salts
94
What two things happen as extracellular calcium concentration rises?
1. Decreased PTH
| 2. Decreased PTH concentration decreases salt resporption to point where calcium will be added to the bone
95
How is calcium filtered?
Freely filtered
96
Does calcium get reabsorbed?
Yes
97
Does calcium get secreted?
No
98
How much of calcium present in the body are we filtering?
Very small percentage
99
What percent of calcium filtered load is reabsorbed in the proximal tubule?
65%
100
What percent of calcium filtered load is reasborbed in the proximal tubule?
25-30%
101
What percent of calcium filtered load is reabsorbed in the distal tubule/collecting tubule?
4-9 % filtered load
102
What percent of calcium filtered load is actually excreted?
1%; but changes as plasma concentration changes (intake changes)
103
What percent of calcium absorbed in the proximal tubule is carried by water via paracellular pathway?
80%
104
What percent of calcium absorbed in the proximal tubule is via transcellular pathway?
20%
105
Diffusion of calcium through luminal membrane into cell driven by what?
Chemical gradient (higher [Ca++] in lumen that inside cell) and electrical gradient
106
how is calcium pumped out of the cell?
Across basolateral border
| Ca ATPase pump/ Na/Ca counter-transport
107
The paracellular pathway accounts for what percent of calcium reabsorption in the loop?
50%
108
Calcium undergoes passive diffusion down what type of gradient in the loop?
Electrical gradient; lumen has slight positive charge compared to interstitial fluid
109
Transcellular pathway accounts for what percent of calcium reabsorption in the lop?
50%; active process
110
Active process of transcellular pathway reabsorption of Ca++ in thick ascending loop stimulated by what?
PTH (most important), Vitamin D (calcitrol), calcitonin
111
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
112
Increased PTH ___________(increases/decreases) Ca++ reabsorption in the distal tubule. What else increases calcium reabsoprtion?
Increases; increased by Vitamin D and calcitonin
113
Where does PTH have no effect on calcium reabsopriton?
Proximal tubule
114
What ion concentration affects [PTH]?
[Phosphate]; as [Phosphate] increases [PTH] increases
115
What ion concentration has major affect on transport mechanisms in the Distal tubule of calcium?
[H+]
116
What is the normal tubular max of phosphate?
0.1 mMol/min
117
If filtered load is under Tmax, how much of phosphate is reabsorbed?
All
118
If filtered load is over Tmax, how much of phosphate is reabsorbed?
Phosphate is actually exctreted
119
What is the plasma threshold for phosphate?
0.8 mMol/L
120
What is the normal plasma concentartion of phosphate?
1 mMol/L; large intake of phosphate each day (milk and meat)
121
In the proximal tubule, what percent of phosphate is reabsorbed?
75-80% of filtered phosphate is reabsorbed
122
What is the distal tubule, what percent of phosphate is reabsorbed?
10%
123
Ine the collecting duct, what percent of phosphate is reabsorbed?
very small amounts
124
What percent of phosphate is excrted?
10%
125
Phosphate Tmax changes based on what?
Intake. Low intake, Tmax will increase over time
126
What two things regulate phosphate?
Tmax and PTH
127
As PTH increases bone resorption of calcium, what else is resorbed?
phosphate
128
Increased PTH _________(increases/decreases) T max for phosphate so less phosphate is reabsorbed and more is excreted.
decreases
129
What percent of magnesium is stored in bone?
>50%
130
Where is most of the magnesium that is not stored in bone?
Intracellular volume
131
What percent of magnesium is in extracellular volume?
<1%
132
What is the total plasma magnesium?
1.8 mEq/L
133
What percent of magnesium is bound to plasma proteins?
>50%
134
Free ionized magnesium is what concentration
0.8 mEq/L
135
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)
136
What is the amount of magnesium that the kidneys much excrete each day?
Total amount absorbed
137
Renal excretion of magnesium is
10 to 15 of filtered load
138
Magnesium reabsorption is what percent in the proximal tubule?
25%
139
Magnesium reabsorption what percent in the loop of henle?
65%
140
Magnesium reabsorption is what percent in distal tubule/collecting duct?
<5%
141
Increased magnesium = _________ reabsorption = _____________excretion.
Decreased, increased
142
Increased magnesium EC fluid volume results in ____________ reabsorption and ___________ excretion.
decreased, increased
143
increased calcium results in _______________ reabsorption and __________ excretion.
decreased, increased
