Potassium Control Flashcards
Where is most the potassium in the body stored?
98% in ICF
Why is maintain ECF [K+] critical?
Its effect on resting membrane potential
Its effects on the excitability of cardiac tissue
How is ECF K+ regulated?
Internal balance - immediate control
External balance - longer term
What happens to potassium after a meal?
Absorbed by intestine and colon
Goes into blood
Moves into cells immediately
Kidneys excrete it in 6-12 hours
What is internal balance?
Movement of potassium between ECF and ICF
What makes up internal balance?
Movement of K+ from ECF into cells
- Na-K-ATPase
Movement of K+ out of cells into ECF
- K+ channels
What factors increase K+ uptake by cells?
Hormones
- insulin
- aldosterone
- catecholamines
Increased ECF [K+]
Alkalosis
What factors promote K+ shift out of cells?
Exercise Cell lysis Increase in ECF osmolality Low ECF [K+] Acidosis
What is the effect of insulin on potassium movement?
Increases Na-K-ATPase activity - increases k+ uptake
What is the effect of aldosterone on potassium movement?
Increases Na-K-ATPase activity - increases k+ uptake
What is the effect of catecholamines on potassium movement?
Increases Na-K-ATPase activity - increases k+ uptake
What is the effect of exercise on potassium?
Exercise increases [K+]
- release of k+ during recovery phase of AP
- muscle damage releases K+
Non-contracting tissues - uptake K+
Exercise releases catecholamines - increases K+ intake by cells
What is external balance?
Excretion of K+
Where is potassium reabsorbed in the kidney?
PCT
Thick ascending limb of LOH
DCT
CD - intercalated cells
Where is potassium secreted in the kidney?
DCT
Cortical collecting duct - principal cells
How is K+ secreted by principal cells?
Basolateral membrane - Na-K-ATPase acitivity increases intracellular K+
High intracellular K+ creates gradient
Na moves in via ENaC - creates electrical gradient
K+ secreted down gradient via channels
What tubular factors increase K+ secretion by principal cells?
ECF [K+]
- stimulates Na-K-ATPase
- increases permeability of apical K+ channels
- stimulates aldosterone secretion
Aldosterone
- increases transcription of proteins for transporters
Acidosis
- decreases K+ secretion
- inhibits Na-K-ATPase
- decreases k+ channel permeability
Alkalosis
- increases K+ secretion
- stimulates Na-K-ATPase
- increases K+ channel permeability
What luminal factors affect K+ secretion by principal cells?
Increased distal tubular flow rate
- washes away luminal k+
- increases K+ loss
Increased Na delivery to distal tubule
- more Na absorbed
- results in K+ loss
How is K+ absorbed by intercalated cells?
Active process mediated by H-K-ATPase
What can cause hyperkalaemia?
Increased intake Decreased renal excretion DKA Cell Lysis Metabolic acidosis
What are the clinical features of hyperkalaemia?
Altered excitability of the heart - arrhythmias
GI neuromuscular dysfunction - paralytic ileus
Acidosis
What are the ECG changes in hyperkalaemia?
Tall T wave
Prolonged PR interval
How is hyperkalaemia managed?
IV calcium gluconate
Glucose + insulin IV
What can cause hypokalaemia?
Excessive loss - GI or renal
Problems with internal balance
