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Renal Final > DSA- Introduction of Regulation of K, Ca, P, Mg Balance > Flashcards

DSA- Introduction of Regulation of K, Ca, P, Mg Balance Flashcards

1
Q

What is the normal ranges of plasma K+ concentration?

A

3.5-5.0 mEq/L

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2
Q

How much K+ is in the body of a 70 kg human?

A

3500 mEq K+

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3
Q

What is the breakdown of K+ in the body?

A

98% intracellular
- 80% muscle cells (~150 mEq/L)
- 20% other cells
2% extracellular (3.5-5.0 mEq/L)

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4
Q

What is responsible for the 30 fold difference in concentration between ICF and ECF?

A

***Na-K-ATPase (ubiquitous)
NKCC2
K+ channels
transcellular distribution regulated by “other” factors/hormones

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5
Q

Besides muscle, what other cells store a significant amount of K+?

A

liver, bone, erythrocytes

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6
Q

What is hypokalemia? What are common causes?

A

Plasma [K+] < ~3.7 mEq/L

Causes: vomiting/diarrhea, insulin excess, deficiency of K+, alkalosis

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7
Q

What is hyperkalemia? What are common causes?

A

plasma [K+] > ~5.2 mEq/L
>10 mEq/L = lethal

Causes: excessive intake, tissue release (rhabdomyolysis, burns, hemolysis), shifts from ICF to ECF (acidosis, insulin deficiency, tissue damage, hyperglycemia)

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8
Q

What is pseudohyperkalemia?

A

artificially high plasma [K+] due to lysis of RBCs while blood is drawn

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9
Q

What is administered as the third drug in lethal injection protocols?

A

KCl

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10
Q

Where is most of the K+ excreted?

A

mostly in urine, some in feces

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11
Q

Where is K+ stored in the body?

A

mostly in muscle cells, liver, bone, RBCs

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12
Q

Do the kidneys filter, secrete, or reabsorb K+?

A

both - depends on diet

input = output

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13
Q

How does hypokalemia affect RMP of most cells?

A

lowers RMP
hyperpolarizes the membrane
harder to reach threshold

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14
Q

How does hyperkalemia affect RMP of most cells?

A

increases RMP
hypopolarizes the membrane
easier to reach threshold

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15
Q

Why does the cardiac conduction system respond opposite to most cells in hypo and hyper -kalemia?

A

K+ channels increase conductance in hyperkalemia that membrane becomes hyperpolarized and less likely to fire –> bradycardia
hypokalemia –> tachycardia

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16
Q

What is hyperkalemia associated with in the heart?

A

bradycardia, peaked T wave

severe hyperkalemia leads to ventricular fibrilation

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17
Q

What is hypokalemia associated with in the heart?

A

tachycardia, low T wave

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18
Q

How do hyperkalemia and hypokalemia affect the membrane of cells in the cardiac system and other cells?

A 
hyperkalemia
     - cardiac: hyperpolarizes membrane
     - other: hypopolarizes membrane
hypokalemia
     - cardiac: hypopolarizes membrane
     - other: hyperpolarizes membrane
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19
Q

What happens when there is a net loss of K+ intracellularly? Net gain?

A

net loss: cell shrinkage

net gain: cell swelling

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20
Q

What happens to the intracellular pH when there is low plasma [K+]?
high plasma [K+]?

A

low: cell acidosis
high: cell alkalosis

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21
Q

What cell enzymes are dependent on K+?

A

some ATPases, succinic dehydrogenase

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22
Q

What function does K+ have on DNA/protein synthesis/growth?

A

lack of K+ leads to reduction of protein synthesis and stunted growth

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23
Q

What happens to the membrane when the ratio of [K+]i/[K+]o is reduced?
increased?

A

reduced: membrane depolarization
increased: membrane hyperpolarization

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24
Q

What happens to neuromuscular activity when plasma [K+] is low?
high?

A

low: muscle weakness, muscle paralysis, intestinal distension, respiratory failure
high: initially increased muscle excitability; later, muscle weakness (paralysis)

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25
Q

What happens to cardiac activity with low plasma [K+]?

high?

A

low: prolonged repolarization; slowed conduction; abnormal pacemaker activity, leading to tachyarrhythmias
high: enhanced repolarization; slowed conduction, leading to bradyarrhythmias and cardiac arrest

26
Q

What happens with low or high plasma [K+] with vascular resistance?

A

low: vasoconstriction
high: vasodilation

27
Q

What is the effect of insulin on potassium?

A

enhanced cell uptake

  • Na-K-ATPase
  • Na-K-2Cl in adipocytes
28
Q

What is the effect of beta-catecholamines on potassium?

A

enhanced cell uptake

- Na-K-ATPase

29
Q

What is the effect of alpha-catecholamines on potassium?

A

impaired cell uptake

- Na-K pump

30
Q

What is the effect of acidosis on potassium?

A

metabolic acidosis inhibits cell uptake more than respiratory acidosis –> hyperkalemia

31
Q

What is the effect of alkalosis on potassium?

A

enhanced cell uptake
Enhanced exchange of intracellular H + for extracellular Na + via the amiloride-sensitive Na + H + antiporter would accelerate cellular potassium accumulation by stimulating the Na,K-ATPase pump.

32
Q

What is the effect of external potassium balance on potassium?

A

loose correlation

33
Q

What is the effect of cell damage on potassium?

A

impaired cell uptake

34
Q

What is the effect of hyperosmolality on potassium?

A

enhanced cell efflux

35
Q

What is adequate intake of calcium to ensure nutritional needs?

A

~1000 mg/day (adults)

36
Q

What is the best dose for calcium absorption?

A

<500 mg

recommend splitting a supplemental dose into morning and evening doses to obtain 1000 mg/day

37
Q

Who is at highest risk for calcium deficiency?

What are other groups at risk for calcium deficiency?

A

Adolescents
postmenopausal women
vegetarians
lactose intolerant

38
Q

Where is calcium stored in the body?

A

bone

39
Q

Where do we get calcium?

A

diet (~1000 mg/day)

40
Q

How is calcium excreted?

A

stool (~800 mg/day)

urine (~200 mg/day)

41
Q

What mediates calcium absorption from GI?

A

calcitrol

42
Q

What mediates bone formation with calcium?

A

calcitonin

43
Q

What mediates calcium resorption from bone?

A

PTH, calcitrol

44
Q

What inhibits calcium excretion from kidneys to urine?

A

PTH, calcitrol

45
Q

What is the normal plasma concentration for calcium?

A

5.0 mEq/L

46
Q

What is the effect of hypocalcemia on neuromuscular excitability?

A

INCREASES neuromuscular excitability
threshold is closer to RMP
hypocalcemic tetany/spasticity

47
Q

What is the effect of hypercalcemia on neuromuscular excitability?

A

DEPRESSES neuromuscular excitability

threshold shifts away from RMP

48
Q

What regulates the plasma calcium levels?

A

PTH, calcitonin, calcitrol

49
Q

What is the DDx for elevated serum calcium?

A

primary hyperparathyroidism

malignancy

50
Q

What is the DDx for low serum calcium?

A

hypoparathyroidism
renal disease
vitamin D deficiency

51
Q

What is adequate phosphorus dietary intake?

A

~1500 mg/day

52
Q

If ~1500 mg of phosphorus is the dietary intake, how much is absorbed and secreted into the gut?
What is the net phosphorus absorbed per day?

A

1100 mg absorbed
200 mg secreted into gut
900 mg net absorbed/day

53
Q

Where is phosphate stored in the body?

A

85% bone
14% cells
1% serum

54
Q

How is phosphate excreted from the body?

A

mostly urine

some feces

55
Q

What are the 4 main regulators of phosphate metabolism?

A
  1. dietary phosphate intake and absorption
  2. calcitrol increases phosphorus resorption from bone and absorption from intestine
  3. PTH influences phosphorus resorption directly from bone and indirectly activates intestinal absorption through stimulation of calcitrol production
  4. renal tubular reabsorption of phosphorus is stimulated by tubular filtered load of phosphorus and inhibited by PTH
56
Q

Where is magnesium stored in the body?

A

50% in bone
49% in ICF (especially muscle)
1% in ECF

57
Q

What are magnesium’s functions?

A

nucleotide binding, enzymatic cofactor, glycolysis, proliferation

58
Q

What is Mg2+ depletion associated with?

A

migraine, depression, epilepsy, SIDS (hypothetical), arrhythmia, preeclampsia, muscle cramps

59
Q

What percent of Mg2+ is stored in muscle?

A

25-30%

60
Q

What is the total serum Mg2+?

A

1.8 mEq/L (1.8-2.2 mg/dL)

61
Q

What is the normal free serum Mg2+?

A

0.8-1.0 mEq/L

Renal Final (7 decks)

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