Regulation Of Potassium Balance Flashcards
What is the normal range for K+?
3.5-5.0 mEq/L
Where is the majority of K+ stored in the human body?
Intracellularly
More specifically in muscle cells (80%)
What are some causes of hypokalemia?
Vomiting/diarrhea
Insulin excess
Alkalosis
Deficiency
What are some causes of hyperkalemia?
Excessive intake Tissue release (rhabdo, 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 are the major routes of potassium loss from the body?
Most is through the kidneys/urine
The rest is through feces
What occurs to the resting membrane potential when the person is hyperkalemic?
The resting membrane potential hypopolarizes, making it more likely to fire
What occurs to the resting membrane potential in a patient with hypokalemia?
The resting membrane potential hyperpolarizes, making it more difficult to fire an AP
What is a classic sign of hypokalemia in an EKG?
Low T-wave
What is a classic sign for hyperkalemia on an EKG?
A high peaked T-wave
What is the adequate intake of Calcium to ensure nutritional needs?
~1000mg/day
Better to split the 1000 up for better absorption
What groups are at highest risk of calcium deficiency?
Adolescents, postmenopausal women, vegetarians, lactose intolerant
What are the 3 methods of acquiring calcium?
Intestinal absorption
Renal tubular reabsorption
Internal redistribution from bone
How is calcium disposed of from the body?
Lost through stool, urine, and distribution into bone
What is the total plasma level of calcium?
5.0 mEq/L
What occurs to muscle in relation to hypocalcemia?
Increases neuromuscular excitability
What occurs to muscle in relation to hypercalcemia?
Depresses neuromuscular excitability
How much is required for daily phosphorus dietary intake?
How much is actually absorbed?
~1500 mg
~900 mg
Where is most of phosphate stored in the body?
85% is stored in the bone
How is phosphate disposed of from the body?
Through stool, urine, and distribution into bone
There’s very little actively in circulation
What are the 4 main regulators of phosphate metabolism?
Dietary phosphate intake
Calcitriol (increases phosphorus resorption)
PTH (resorbs from bone)
Renal tubular reabsorption
Where is most of Mg2+ stored in the body?
50% in bone
With 49% in ICF (especially muscle) and 1% in ECF
Very little actively circulates
What is the total serum Mg2+ level?
How about free serum Mg2+?
- 8-2.2 mg/dL
0. 8-1.0 mEq/L
What effect does epinephrine have on potassium?
It lowers serum K+ by uptake into cells of extrarenal tissues while stimulating potassium excretion by the kidney
DECREASES SERUM K+
What is the effect of insulin on potassium?
It stimulates Na-K ATPase causing a flux of K+ into cells and efflux of Na+ from cells
INCREASES INTRACELLULAR K+
What effect does aldosterone have on potassium?
Renal: INCREASES K+ EXCRETION
Extrarenal: INCREASES K+ SECRETION INTO INTESTINAL FLUIDS AND SALIVA
What do insulin and catecholamines stimulate?
They both upregulate the Sodium-Hydrogen exchanger, the NKCC, and Na-K ATPase
This promotes a net effect of bringing potassium in and pumping hydrogen out
What is the major mechanism in the proximal tubule?
The Na-K ATPase in the basolateral membrane
How is potassium reabsorbed in the proximal tubule?
Because Na gets reabsorbed with HCO3, Cl- gets left behind creating a negative transepithelial difference (TEPD), which eventually repels Cl too, causing it to get reabsorbed
This NaCl reabsorption leads to water following along and creating a positive TEPD, which then begins to repel K+, so it moves paracellularly
Where is potassium secreted and reabsorbed?
In the late DT and cortical CD
What do principal cells and beta-intercalated cells do with potassium
They secrete it into the tubular lumen
Stimulated by increased ECF [K+], aldosterone, and increased tubular flow rate
What do alpha-intercalated cells do with potassium?
They reabsorb it
Stimulated by K+ deficiency, low K+ diet, hypokalemia, or K+ loss through SEVERE diarrhea
If there is an increased distal tubular flow rate, what occurs to potassium?
It enhances K+ secretion
And vice versa
If there is acute alkalosis, how does this affect K+ levels?
There is increased activity of the Na-K ATPase pump, which leads to increased potassium secretion and therefore HYPOKALEMIA
If there is acute acidosis, what is the affect on K+ levels?
There is decreased activity of the Na-K ATPase pump and decreases K+ secretion and therefore HYPERKALEMIA
What is the difference between acute and chronic acidosis?
Chronic acidosis stimulates K+ secretion
What effect does ADH have on K+?
Increased K+ secretion
What effect does luminal flow rate have on K+?
Increased flow rate = increased K+ secretion
What effect do glucocorticoids have on K+?
Increased K+ secretion
If there is an increase in NaCl reabsorption, what occurs to K+ levels?
There is a decrease in K+ secretion due to the decrease of the negative TEPD
