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)
