Session 6 - Control of Potassium (OK+?) Flashcards Preview

Semester 3 - Urinary > Session 6 - Control of Potassium (OK+?) > Flashcards

Flashcards in Session 6 - Control of Potassium (OK+?) Deck (67)
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What % of K+ is in the ICF?

• 98%
• 120-150mmol


What % K+ is in the ECF?

• 2%
• 3.5 - 5 mmol/l


What is the difference between ICF & ECF maintained by?

Na+/K+ ATPase


How does K+ establish the resting membrane potential?

• Diffusion out of ICF into ECF
• Gives resting cell membrane potential of -90mv


What does an increase in ECF K+ cause?

• Depolarisation of cell membrane


What do a decrease in ECF K+ cause?

Hyperpolarization of the cell


Give a brief overview of K+ ions

• K+ ions are the most abundant intra-cellular cation
• 98% of total body K+ content is intracellular
• 2% is in the ECF

Body tightly maintains plasma K+ in the range of 3.5 - 5.3 mmo


Why is high K+ inside cells and mitochondria necessary?

Maintaining cell volume
Regulating intracellular pH
Controlling cell-enzyme function
DNA/Protein synthesis
Cell growth


What are the metabolic effects of extremely low extracellular K+?

• Inability of the kidney to form concentrated urine
• A tendency to develop metabolic alkalosis

Large enhancement of renal ammonium excretion


Why is low K+ necessary outside cells?

• To maintain steep K+ ion gradient across cell membranes
• Increase in ECF K+ depolarises cell membrane
• Decrease in ECF K+ hyperpolarises the cell membrane


How is potassium regulated?

• Internal balance, maintaining ECF K+
• External balance, adjusts K+ excretion to intake


What is average K+ intake in diet?

40 - 100 mmol/day


How does body prevent huge increase in ECF K+ after eating?

• K+ moves into cells
• Kidneys begin to excrete K+


What is internal balance the net result of?

• Movement of K+ from ECF -> into cells
• Movement of K+ out of cells into ECF


What factors promote the uptake of K+ into cells?

• Hormones
○ Insulin
○ Aldosterone
○ Catecholamines
• Alkalosis
○ Shift of H+ out of cells
○ Reciprocal K+ shift into cells
• Increased K+ in ECF


How does insulin promote uptake of K+ in ECF?

• K+ in splanchnic blood stimulates insulin secretion by pancreas

Insulin stimulates K+ uptake by muscle cell and liver via an increase in Na+/K+ ATP-ase


How does aldosterone promote excretion of K+ into tubule lumen

• Increases the transcription of Na/K/ATPase in basolateral membrane and ENaC/K+ channels in apical membrane
• Increased channel number gives increases K+ excretion


What factor can stimulate aldosterone secretion?

• Hyperkalaemia


How do catecholamines increase uptake of K+ in ECF?

• Act via B2 adrenoreceptors which in turn stimulate Na-K+-ATPase


Outline 5 factors promoting K+ shift out of cell

• Low ECF
• Exercise
• Cell lysis
• Increase in ECF osmolality
• Acidosis - Increase ECF
○ Acidosis, shift of H+ into cells, reciprocal K+ shift out of cells


How does exercise promote K+ shift of cells?

• Skeletal muscle contraction -> Net release of K+ during recovery phase of action potential
• Increase in plasma K+ which is proportional to the intensity of exercise
• Uptake of K+ by non contracting tissues as a result of catecholamine release


How do catecholamines offset ECF rise in K+ during exercise?

• By increasing K+ uptake to other cells


How does cell lysis promote K+ shift out of cells

• Cell lysis causes a release of K+ from ICF into the ECF
• Can be causes by skeletal muscle trauma, intravascular haemolysis and cancer chemotherapy


How does plasma tonicity cause K+ movement from ICF to ECF?

• Increase in plasma & ECF tonicity
• Water moves from ICF into ECF
• Increase in K+ in ICF

K+ moves down conc grad out of cell


What does acidosis do to K+ conc in cell?

• Shift of H+ into cells
• Reciprocal K+ shift
• Out of the cells
• Causes hyperkalaemia


What does akalosis do to K+ concentration in cell?

• Shift of H+ out of cells
• Reciprocal K+ shift
• Move into cells causes hypokalaemia


How is potassium balanced?

• External balance
• Internal balance


What is external balance?

• Regulates total body K+ content
• Depends on dietary intake, and excretion
• Responsible for the long-term control of K+


How is external balance controlled?

• Controlled by renal excretion


What is internal balance?

• Regulates K+
• Responsible for moment to moment control
• If ECF/Plasma (K+) increases, K+ moves into cells ○ ECF -> ICF
○ Na/K/ATPase
• If ECF/plasma K+ decreases, K+ moves out of cells
○ ICF -> ECF
○ K+ channels