Urinary 4 - Control of K+ Flashcards
Where is the majority of K+ found in the body?
Intracellular fluid of:
- Skeletal muscle cells
- Liver cells
- RBCs
- Bone cells
What is the approximate intracellular fluid [K+]?
120-150 mM
What is the approximate extracellular fluid [K+]?
3.5-5 mM
Is the concentration of K+ higher in intracellular fluid or extracellular fluid?
Higher [K+] INTRAcellularly
How the the difference of [K+] between the ICF and ECF maintained?
Na+/K+-ATPase
What is the average intake of K+ during a meal?
30 mM
What is the average time taken for excretion of K+ after a meal?
6-12hrs
What are the main treatments used for hyperkalaemia?
- IV Insulin and Dextrose
- IV Calcium Gluconate
- Salbutamol
Why is Insulin and Dextrose given to treat hyperkalaemia?
Insulin stimulates Na+/K+-ATPase (increasing absorption of K+ into cells)
Dextrose prevents hypoglycaemia occurring
Hyperkalaemia stimulates the secretion of which 2 hormones? Why?
1) Insulin
2) Aldosterone
(Also catecholamines)
These increase Na+/K+-ATPase activity, driving K+ absorption into cells to decrease the ECF [K+]
What percentage of K+ is reabsorbed in the PCT?
67%
In what part of the tubule does the majority of K+ reabsorption occur?
PCT
What percentage of K+ is reabsorbed in the TAL (Thick ascending limb of LoH)?
20%
via what channel is K+ reabsorbed across the apical membrane of the TAL cells (Thick ascending limb of LoH)?
Na+/K+/2Cl- symporter (NKCC2)
In what part of the tubule is K+ passively reabsorbed?
PCT
In what part of the tubule is K+ actively reabsorbed?
- TAL (thick ascending limb of LoH)
- Distal tubule
- Collecting duct
What type of cell actively reabsorbs K+ from the lumen of the late distal tubule and early collecting duct? What channel mediates this active reabsorbtion?
Alpha Intercalated cells
H+/K+-ATPase
What cells of the tubule secrete K+? What channels are involved?
Principle cells (of late DT and early CD)
Na+/K+-ATPase on the basolateral membrane
ROMK on the apical membrane
How would acidosis affect K+ secretion into the tubular lumen?
Inhibits Na+/K+-ATPase = inhibits K+ secretion
How would an increase in Aldosterone affect K+ secretion into the tubular lumen?
Increase K+ secretion
Name the main causes of HYPERkalaemia:
- Increased intake
- Cell lysis (tumour/trauma)
- Exercise
- Decreased renal excretion (AKI/CKI/drugs)
- Diabetic ketoacidosis
- Metabolic acidosis
How does DKA and metabolic acidosis lead to hyperkalaemia?
Acidosis inhibits the Na+/K+-ATPase, inhibiting K+ renal secretion
How does exercise cause an increase in serum K+? How does the body reverse this quickly?
- K+ released from muscle cells during exercise as Na+/K+-ATPase cannot keep up with the repeated repolarisation
- Exercise causes increase in catecholamines, which increase activity of Na+/K+-ATPase, driving the uptake of K+ back into the cells
What are the common symptoms of hyperkalaemia?
- Heart abnormalities (arrhythmias, bradycardia)
- Fatigue and muscle weakness
In an emergency situation, how would you remove excess K+ from a hyperkalaemic patient?
Dialysis
Name some of the common causes of HYPOkalaemia:
- Excessive loss (diarrhoea, vomiting, diuretic drugs)
- Reduced intake (malnourished/eating disorders)
- Metabolic alkalosis
What are the common symptoms of hypokalaemia?
- Irregular heatbeat / palpitations
- Constipation
- Muscle weakness/tingling
