DSA- Introduction of Regulation of K, Ca, P, Mg Balance Flashcards
What is the normal ranges of plasma K+ concentration?
3.5-5.0 mEq/L
How much K+ is in the body of a 70 kg human?
3500 mEq K+
What is the breakdown of K+ in the body?
98% intracellular
- 80% muscle cells (~150 mEq/L)
- 20% other cells
2% extracellular (3.5-5.0 mEq/L)
What is responsible for the 30 fold difference in concentration between ICF and ECF?
***Na-K-ATPase (ubiquitous)
NKCC2
K+ channels
transcellular distribution regulated by “other” factors/hormones
Besides muscle, what other cells store a significant amount of K+?
liver, bone, erythrocytes
What is hypokalemia? What are common causes?
Plasma [K+] < ~3.7 mEq/L
Causes: vomiting/diarrhea, insulin excess, deficiency of K+, alkalosis
What is hyperkalemia? What are common causes?
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)
What is pseudohyperkalemia?
artificially high plasma [K+] due to lysis of RBCs while blood is drawn
What is administered as the third drug in lethal injection protocols?
KCl
Where is most of the K+ excreted?
mostly in urine, some in feces
Where is K+ stored in the body?
mostly in muscle cells, liver, bone, RBCs
Do the kidneys filter, secrete, or reabsorb K+?
both - depends on diet
input = output
How does hypokalemia affect RMP of most cells?
lowers RMP
hyperpolarizes the membrane
harder to reach threshold
How does hyperkalemia affect RMP of most cells?
increases RMP
hypopolarizes the membrane
easier to reach threshold
Why does the cardiac conduction system respond opposite to most cells in hypo and hyper -kalemia?
K+ channels increase conductance in hyperkalemia that membrane becomes hyperpolarized and less likely to fire –> bradycardia
hypokalemia –> tachycardia
What is hyperkalemia associated with in the heart?
bradycardia, peaked T wave
severe hyperkalemia leads to ventricular fibrilation
What is hypokalemia associated with in the heart?
tachycardia, low T wave
How do hyperkalemia and hypokalemia affect the membrane of cells in the cardiac system and other cells?
hyperkalemia
- cardiac: hyperpolarizes membrane
- other: hypopolarizes membrane
hypokalemia
- cardiac: hypopolarizes membrane
- other: hyperpolarizes membraneWhat happens when there is a net loss of K+ intracellularly? Net gain?
net loss: cell shrinkage
net gain: cell swelling
What happens to the intracellular pH when there is low plasma [K+]?
high plasma [K+]?
low: cell acidosis
high: cell alkalosis
What cell enzymes are dependent on K+?
some ATPases, succinic dehydrogenase
What function does K+ have on DNA/protein synthesis/growth?
lack of K+ leads to reduction of protein synthesis and stunted growth
What happens to the membrane when the ratio of [K+]i/[K+]o is reduced?
increased?
reduced: membrane depolarization
increased: membrane hyperpolarization
What happens to neuromuscular activity when plasma [K+] is low?
high?
low: muscle weakness, muscle paralysis, intestinal distension, respiratory failure
high: initially increased muscle excitability; later, muscle weakness (paralysis)
What happens to cardiac activity with low plasma [K+]?
high?
low: prolonged repolarization; slowed conduction; abnormal pacemaker activity, leading to tachyarrhythmias
high: enhanced repolarization; slowed conduction, leading to bradyarrhythmias and cardiac arrest
What happens with low or high plasma [K+] with vascular resistance?
low: vasoconstriction
high: vasodilation
What is the effect of insulin on potassium?
enhanced cell uptake
- Na-K-ATPase
- Na-K-2Cl in adipocytes
What is the effect of beta-catecholamines on potassium?
enhanced cell uptake
- Na-K-ATPase
What is the effect of alpha-catecholamines on potassium?
impaired cell uptake
- Na-K pump
What is the effect of acidosis on potassium?
metabolic acidosis inhibits cell uptake more than respiratory acidosis –> hyperkalemia
What is the effect of alkalosis on potassium?
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.
What is the effect of external potassium balance on potassium?
loose correlation
What is the effect of cell damage on potassium?
impaired cell uptake
What is the effect of hyperosmolality on potassium?
enhanced cell efflux
What is adequate intake of calcium to ensure nutritional needs?
~1000 mg/day (adults)
What is the best dose for calcium absorption?
<500 mg
recommend splitting a supplemental dose into morning and evening doses to obtain 1000 mg/day
Who is at highest risk for calcium deficiency?
What are other groups at risk for calcium deficiency?
Adolescents
postmenopausal women
vegetarians
lactose intolerant
Where is calcium stored in the body?
bone
Where do we get calcium?
diet (~1000 mg/day)
How is calcium excreted?
stool (~800 mg/day)
urine (~200 mg/day)
What mediates calcium absorption from GI?
calcitrol
What mediates bone formation with calcium?
calcitonin
What mediates calcium resorption from bone?
PTH, calcitrol
What inhibits calcium excretion from kidneys to urine?
PTH, calcitrol
What is the normal plasma concentration for calcium?
5.0 mEq/L
What is the effect of hypocalcemia on neuromuscular excitability?
INCREASES neuromuscular excitability
threshold is closer to RMP
hypocalcemic tetany/spasticity
What is the effect of hypercalcemia on neuromuscular excitability?
DEPRESSES neuromuscular excitability
threshold shifts away from RMP
What regulates the plasma calcium levels?
PTH, calcitonin, calcitrol
What is the DDx for elevated serum calcium?
primary hyperparathyroidism
malignancy
What is the DDx for low serum calcium?
hypoparathyroidism
renal disease
vitamin D deficiency
What is adequate phosphorus dietary intake?
~1500 mg/day
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?
1100 mg absorbed
200 mg secreted into gut
900 mg net absorbed/day
Where is phosphate stored in the body?
85% bone
14% cells
1% serum
How is phosphate excreted from the body?
mostly urine
some feces
What are the 4 main regulators of phosphate metabolism?
- dietary phosphate intake and absorption
- calcitrol increases phosphorus resorption from bone and absorption from intestine
- PTH influences phosphorus resorption directly from bone and indirectly activates intestinal absorption through stimulation of calcitrol production
- renal tubular reabsorption of phosphorus is stimulated by tubular filtered load of phosphorus and inhibited by PTH
Where is magnesium stored in the body?
50% in bone
49% in ICF (especially muscle)
1% in ECF
What are magnesium’s functions?
nucleotide binding, enzymatic cofactor, glycolysis, proliferation
What is Mg2+ depletion associated with?
migraine, depression, epilepsy, SIDS (hypothetical), arrhythmia, preeclampsia, muscle cramps
What percent of Mg2+ is stored in muscle?
25-30%
What is the total serum Mg2+?
1.8 mEq/L (1.8-2.2 mg/dL)
What is the normal free serum Mg2+?
0.8-1.0 mEq/L
