Potassium

Question 1

Principal cation in _____-cellular fluid
- total body K
- ICF
- skeleton
- ECF

Answer 1

intra
3800 mmol
3200 mmol
300 mmol
80 mmol

Question 2

Potassium Functions

Answer 2

• Maintains cell integrity, fluid & electrolyte balance and pH
• Key role (with sodium) in resting membrane potentials and action potentials
• nerve impulse transmission and muscle contraction
• So influences contractility of smooth, skeletal & cardiac muscle & nerve tissue
  excitability
• Also influences electrolyte & pH balance
• Maintaining consistent extracellular fluid (ECF) K [ ] in the blood is CRITICAL
• Small increases in ECF [ ] depolarizes membranes
• Small decrease in ECF [ ] increases the ratio, hyperpolarizes membranes &
  raises threshold for excitation
• Therefore aberrations can paralyse muscle & stop the heart

Question 3

Absorption & Transport

Answer 3

• Absorption throughout the small intestine and to a lesser extent the
  large intestine
• > 85% is absorbed
• K+/H+ ATPase pump mediated absorption
• Absorption managed hormonally to a large extent by the action of
  insulin, which promotes active potassium uptake by hepatic and muscle
  cells.
• Diffuses across basolateral membrane into circulation via a K+ channel

Question 4

Potassium balance

Answer 4

• Controlled by uptake into cells (promoted by
  insulin) and excretion by kidneys
• Kidney excretion increased by higher
  extracellular potassium concentration,
  aldosterone
• Controlled by the same hormones as Na but in
  the opposite direction
• Balance is compromised by kidney diseases-
  potassium content of diets important
• K intake DECREASES
  Calcium excretion

Question 5

Sources of potassium

Answer 5

• Found in all living cells (plant and animals)
• Rich sources include avocados, bananas,
  mango, leafy green vegetables, honeydew
  melon. Other good sources include milk
  yoghurt (see p. 466 textbook for details)
• Can be added to processed foods as salt
  substitute (potassium chloride)
• Fresh foods higher than processed foods

Question 6

Potassium and Blood Pressure

Answer 6

• Potassium intakes may affect blood pressure
• Particularly in those who are salt sensitive
• K causes the kidneys to excrete excess Na from
  the body
• High potassium intakes in conjunction with low sodium
  intakes may ↓ blood pressure

Question 7

Potassium deficiency

Answer 7

• Potassium depletion- rarely caused by inadequate intakes
  alone,
• Most often results from situations causing profound loss of
  fluids and electrolytes, such as excessive vomiting or diarrhoea
• Also caused by magnesium deficiency (promotes potassium
  excretion), use of diuretic drugs (blood pressure treatment) or
  glucocorticoids (used to suppress inflammation), nephropathies
• “Refeeding syndrome”: when malnourished persons
  (starvation, anorexia etc.) are provided with nutritional
  treatment insufficient in potassium

Question 8

Hypokalemia

Answer 8

Usually due to high GI tract loss –
severe vomiting and diarrhoea.
Can also be part of refeeding
syndrome
* Fatigue, malaise, muscular
weakness, nervous irritability,
disorientation, cardiac arrythmia
* Maybe rectified by food
consumption, potassium infusion

Question 9

Hyperkalemia

Answer 9

• Rare in general population-
  often occurs in conjunction with
  renal damage/disease
• May occur in shock (cells
  release K, decrease blood flow
  to kidneys), crush injuries (cells
  release K and haemoglobin-
  block glomerular filtration),
  anuria and Addison’s disease
• Dangerous- severe cardiac
  arrhythmia and possibly death

Question 10

Assessment of Potassium Status

Answer 10

Biochemistry
- Plasma K [ ]
* Usual K 3.5 to 5.0 mmol/L
* Influenced by multiple factors besides intake
- Urinary K excretion: 24-hr urine collection
* Amount excreted in 24 hr urine reflects intake
* Substantial intra individual variation, so multiple samples
needed to accurately estimate intake
- Clinical symptoms