Contorl Of Potassium Flashcards
Describe the distribution o K+ in body fluids
98% in ICF, only 2% in ECF Mainly in skeletal muscle cells (also liver, red cells, bone)
Shift of 1% of ICF K+ to ECF would raise ECF [K+] by 50%
Difference between ICF & ECF [K+] maintained by Na-K-ATPase Maintaining ECF [K+] is critical
Why is maintaining [K+] critical?
- Because of its effect on the resting membrane potential
- Hence its effects on excitability of cardiac tissue
- Hence risk of life threatening arrhythmias with hyperkalaemia and hypokalaemia
How is ECF K+ regulated
– Immediate Control By internal balance Moves K+ between ECF and ICF – Longer term, overall K+ balance By external balance adjusting renal K+ excretion
What are potassium rich foods
Raisins, honey dew, banana, orange, tomato, potato chips, baked potato, milk
Describe he events following an average meal
• Intestine and colon absorb dietary K+
• E.g. If 28 mmol K+ absorbed
— ECF K+ will increase by 2mmol/L
— If pre-meal K+ was 5 mmol/L could rise to 7 mmol/L (which is a dangerous level)
• But 4/5ths moves into cells within minutes
• After slight delay kidneys begin to excrete K+
Excretion complete in 6 -12 hours
Describe K+ balance following a K+ load eg average meal
See slide
Decsribe the internal balance of K+
Is the net result of
1. Movement of K+ from ECF -> into cells
mediated via Na-K-ATPase
2. Movement of K+ out of cells into ECF
Via K+ channels (channels which determine the K+ permeability of the cell membrane)
What increases K+ uptake by cells
1. Hormones (Act via Na-K-ATPase) • Insulin, • Aldosterone • Catecholamines 2. Increased [K+ ] in ECF 3. Alkalosis - low ECF [H+] K+ shift -> into cells (more later)
What promote K+ shift out of cells
- Exercise
- Cell lysis
- Increase in ECF Osmolality
- Low ECF [K+ ]
- Acidosis - increase ECF [H+]
— K+ shift -> out of cells
(more later)
Describe the effect of K= o insulin
• K+ in splanchnic blood stimulates insulin secretion by pancreas
• Insulin increases Na-K-ATPase activity -> increases K+ uptake by
muscle cells and liver
Clinical Use: I.V. insulin + Dextrose used treat hyperkalaemia
Describ ethe effect of K+ on aldosterone
Aldosterone
– K+ in blood stimulates Aldosterone secretion
– stimulates uptake of K+ via Na-K-ATPase
Desctibe the relation between k+ and catecholamines
Catecholamines
– Acts via B2 adrenoceptors
– Which stimulate Na-K-ATPase and cellular uptake of K+
Describe excerciese and K+
• Net release of K+ during recovery phase of action potential, K+ exits cell (K+ channels open)
• Also skeletal muscle damage during exercise releases K+
• -> increase in plasma [K+] is proportional to the intensity of exercise
• Uptake by non-contracting tissues prevents dangerously high
hyperkalaemia
• Exercise (& trauma) also increase catecholamines, which
offset ECF [K+] rise by increasing K+ uptake by other cells
• Cessation of exercise results in a rapid ↓plasma [K+], often to
<3mmol/L
Describe the acid base disturbances to K+
• Affect several acid-base, Na+ and K+ transport pathways across
cell membrane
• Final result is as if there is a reciprocal shift of H+ and K+
between the cells and ECF
— acidosis shift of H+ into cells, reciprocal shift o K+ out of cells leading to hyperkalaemia
— alkalosis shift of H+ out of cells, reciprocal shift of K+ into cells, leading to hypokalaemia
How can changes in [K+] affect pH
Hypo & Hyperkalaemia Similarly, changes in ECF [K+] causes reciprocal shifts in K+ and H+ between the ECF & ICF
Hyperkalaemia, shift of K+ into cells
Reciprocal H+ shift out of the cells
Hyperkalaemia leads to acidosis
Hypokalaemia shift of K+ out of cells Reciprocal H+ shift into the cells
Hypokalaemia causes alkalosis
