Potassium

Question 1

Is potassium the MAJOR INTRA- or EXTRA-cellular cation?

Answer 1

INTRA

Only 2% of K is found in the extracellular fluid

Question 2

What are the best food sources for K?

Answer 2

Abundant in unprocessed foods, widespread

OJ
Bananas, strawberries
Cantaloupe
Watermelon
Green leafy vegetables
Whole grains
Whole milk

Question 3

How much of K is absorbed?

Answer 3

Over 90%

Question 4

Where is K absorbed?

Answer 4

SI and Colon are involved

Question 5

How is K absorbed?

Answer 5

Depending upon concentration, K is absorbed by passive diffusion or by the K+/H+-ATPase Pump

To enter the blood, K accumulates in the cell, then diffuses across the basolateral membrane via the K+ CHANNEL

Question 6

What are the functions of K? **

Answer 6

1. Maintain electrolyte balance
2. The contractility of smooth, skeletal, and cardiac muscle.
3. The excitability of nerve tissue **

Question 7

Explain the mechanism for how K is brought into the skeletal muscle? (Hint: there are 3).

Answer 7

Through the activation (or binding) of any of these 3 receptors at the SM:

1. Beta-adrenergic receptor
2. Insulin receptor (insulin binding)
3. GLUT-4 receptor (glucose binding)

Results in the uptake of K+ into the cell, via the Na2+/K+ PUMP

You will have SODIUM being pumped OUT & POTASSIUM being pumped IN

Question 8

Resting Potential Difference

Answer 8

The ATP driven sodium-potassium pump maintains an artificially LOW [sodium] and HIGH [K+] in the INTRACELLULAR SPACE, generating this resting potential difference

aka more K+ on the inside and more Na2+ on the outside

Question 9

Explain the 4 phases of muscle stimulation/contraction.

Answer 9

PHASE 4: The end of the contraction, representing the resting potential difference

PHASE 1: There is a stimulation of the cell, so a RAPID DEPOLARIZATION due to the opening of the Na2+ channels that open; resulting in an INCREASE in the membrane potential (aka DEPOLARIZATION).

PHASE 2: There is a plateau due to the opening of some voltage-gated slow Ca2+ channels and the closing of some of the K+ channels. The FLUX of CALCIUM is VERY IMPORTANT (remember!). So, when CALCIUM comes in here, it will bind to those muscle fibers, resulting in CONTRACTION

PHASE 3: REPOLARIZATION due to the opening of voltage-gated K+ channels and the closing of Ca2+ channels. So, POTASSIUM ENTERS and the result is back to the resting potential difference (where there is more K+ on the inside and more sodium on the outside).

Question 10

How is K excreted from the body?

Answer 10

Via the kidneys

Question 11

How is K excretion controlled?

Answer 11

The same hormones as sodium excretion, but in the opposite direction

ALDOSTERONE is secreted in response to HIGH plasma K+ and enhances K+ excretion.

Question 12

When K+ is high in our blood, what hormones will be secreted?

Answer 12

ALDOSTERONE & ADH, in order to enhance K+ excretion to normalize K+ levels

Question 13

What causes K deficiency?

Answer 13

NOT DIETARY INTAKE

It is due to secondary causes, such as:

Increased GI losses due to excessive V,D, intestinal drainage or laxative abuse

Some meds like thiazide (diuretic)

Chronic metabolic acidosis

Leukemia

Question 14

What are the symptoms of a moderate deficiency?

Answer 14

Increase in BP
Increase in Ca2+ excretion
Abnormal bone turnover

Question 15

What are the symptoms of severe deficiency (hypokalemia)?

Answer 15

<3.5 mmol/L

Cardiac arrhythmias, muscular weaknesses, nervous irritability, hypercalciuria, glucose intolerance, mental disorientation, fatigue

Question 16

What is the AI for K?

Answer 16

4,700 mg/d (set by FNB)

Question 17

What is the average K intake in Americans?

Answer 17

3,300 mg daily