Final - Potassium

Question 1

What is potassium’s role in the cell?

Answer 1

it is the major intracellular cation

Question 2

What are the sources of potassium?

Answer 2

abundant in unprocessed foods;

• fruits (orange juice, bananas, cantalope, watermelon)
• green leafy vegetables
• Whole grains
• Milk
• salt substitutes - replace Na+

Question 3

How is potassium absorbed

Answer 3

absorbed across the apical membrane via the K/H+ ATPase pump

Question 4

What are the functions of potassium?

Answer 4

• 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

Question 5

How is potassium excretion regulated?

Answer 5

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

Question 6

What is the major hormone involved in K+ homeostasis?

Answer 6

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

Question 7

How many americans meet the guidelines for potassium?

Answer 7

2% of americans

4.7 g/day (4700 mg)

Question 8

What can cause potassium deficiency?

Answer 8

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

Question 9

What is potassium deficiency called?

Answer 9

Hypokalemia

Question 10

What is the most common cause of hypokalemia?

Answer 10

Excessive renal loss

• increased circulating aldosterone concentration increases sodium reabsorption while enhancing potassium excretion
• Diuretics

Question 11

What are the symptoms of potassium deficiency (hypokalemia)?

Answer 11

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

Question 12

What are the causes of potassium toxicity (hyperkalemia)?

Answer 12

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

Question 13

What are the symptoms of potassium toxicity?

Answer 13

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

Question 14

How does potassium influence hypertension?

Answer 14

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