What is potassium’s role in the cell?
it is the major intracellular cation
What are the sources of potassium?
abundant in unprocessed foods;
- fruits (orange juice, bananas, cantalope, watermelon)
- green leafy vegetables
- Whole grains
- Milk
- salt substitutes - replace Na+
How is potassium absorbed
absorbed across the apical membrane via the K/H+ ATPase pump
What are the functions of potassium?
- contractility of smooth, skeletal and cardiac muscle (muscle relaxation)
- Nerve excitation
- Na/K ATPase exchange (increased by insulin)
- Membrane permeability
- Structural integrity of ribosomes
- Amino acid utilization and protein synthesis
- Acid base balance; ionic role in osmotic pressure
How is potassium excretion regulated?
Dependent on cellular K+ content
- high potassium diet increases intracellular K+ concentration
- concentration gradient favors the secretion of the cation into the lumen–> increased K+ excretion
Aldosterone
- elevated serum K or decreased renal perfusion pressure increases aldosterone synthesis and release
- stimulates K+ excretion (opposite of Na) in the distal tubules by increasing permeability of apical membrane
Active K+ reabsorption in the collecting duct
-K+ reabsorption in the collecting duct is coupled with proton secretion ; catalyzed by a H+/K+ activated ATPase pump
What is the major hormone involved in K+ homeostasis?
Aldosterone
- elevated serum K or decreased renal perfusion pressure increases aldosterone synthesis and release
- stimulates K+ excretion (opposite of Na) in the distal tubules by increasing permeability of apical membrane
How many americans meet the guidelines for potassium?
2% of americans
4.7 g/day (4700 mg)
What can cause potassium deficiency?
increased gastrointestinal losses due to vomiting, diarrhea, intestinal drainage or laxative abuse
re-feeding of malnourished individuals; synthesis of lean body mass
Leukemia
-Excessive renal loss
What is potassium deficiency called?
Hypokalemia
What is the most common cause of hypokalemia?
Excessive renal loss
- increased circulating aldosterone concentration increases sodium reabsorption while enhancing potassium excretion
- Diuretics
What are the symptoms of potassium deficiency (hypokalemia)?
Alterations in cardiac rate, rhythm and conduction
-muscle weakness
depletion of cell K+ leads to: skeletal muscle necrosis acute rhabdomylolysis (disintegration of muscle fibers; products lead to kidney failure) -Nephritis -cardiac cell necrosis -metabolic alkalosis -reduced insulin secretion -reduce intestinal motility
What are the causes of potassium toxicity (hyperkalemia)?
Acute acidosis
severe dehydration
cell death (burn patients, crush injuries)
excessive ingestion
hypoaldosteronism/unresponsivenss to aldosterone
–addison’s disease (adrenal insufficiency)
–Angiotensin -converting enzyme (ACE) inhibitors (hypertension)
Potassium sparing diuretics
Anti rejection medications
What are the symptoms of potassium toxicity?
in severe hyperkalemia:
paralysis of the skeletal muscle occurs Neuromuscular weakness mental confusion Cardiac symptoms --abnormalities of cardiac rhythm, cardiac conduction rate --ventricular tachycardia --flutter and fibrillation of the heart -cardiac arrest
How does potassium influence hypertension?
Studies show an association between increase K+ intake and decreased prevalence of hypertension
-K+ promotes urinary NA+ excretion, diminishing Na+ level
Increased K+ intake reduces excretion of calcium and magnesium
-Calcium and magnesium also decrease blood pressure
