Potassium Control Flashcards
What is the approximate ICF conc for K+?
120-150 mmol/L
What is the approx ECF conc of K+?
3.5 - 5 mmol/L
Why is it critical to maintain the ECF K+ concentration?
Effects the RMP
Effects the excitability of cardiac tissue - risk of life threatening arrhythmias with hyper- or hypokalaemias
Give some examples of potassium rich food
Banana Honey dew melon Raisins Orange Tomato Baked potatoes
What events occur regarding K+ following a meal?
Intestine and colon absorb dietary K+
Potassium conc can rise to a dangerous ECF level
But 4/5 moves into cells within minutes
After a slight delay, kidneys begin to excrete K+
Excretion complete in 6-12 hours
Describe how cells and ECF balance K+
Movement K+ from ECF into cells via Na/K/ATPase
Movement K+ out of cells via K+ channels
What factors increase K+ uptake into cells?
Hormones - insulin, aldosterone, catecholamines
Increased potassium in ECF (concentration gradient)
Alkalosis (shift of H+ out, K+ in)
Give some factors promoting K+ shift out of cells
Exercise Cell lysis Increase ECF osmolarity (Na+ in, K+ out) Low conc K+ in ECF (conc gradient) Acidosis (H+ into cells, K+ out)
How does K+ affect insulin and vice versa?
K+ in splanchnic blood stimulates insulin secretion by pancreas
Insulin increases Na/K/ATPase activity
Increases K+ uptake into cells
How do aldosterone and K+ affect each other?
K+ in blood stimulates aldosterone secretion
Stimulates uptake of K+ via Na/K/ATPase
How do catecholamines affect K+ uptake?
Act via beta 2 adrenoceptors
Stimulate Na/K/ATPase
Increases cellular uptake of K+
Describe the K+ changes during exercise
Net release of K+ during the recovery phase of an action potential
K+ exits cells
Skeletal muscle damage will release K+
Plasma K+ conc proportional to the intensity of exercise
How is dangerous hyperkalaemia prevented in exercise?
Uptake of K+ by non-contraction tissue
Increase catecholamines to increase K+ uptake into other cells
In terms of K+, acidosis leads to …
Hyperkalaemia
In terms of K+, alkalosis leads to…
Hypokalaemia
Where and how in the nephron is K+ reabsorbed?
PCT - passive, paracellular
TAL - active, NKCC2
DCT/CD - intercalated cells
Which cells secrete K+ into the nephron lumen?
Principal cells of DCT and cortical collecting duct
How does aldosterone promote K+ secretion in the kidney?
Increases transcription of the relevant proteins
Na/K/ATPase
K+ channels
ENaC
Why does acidic filtrate decrease K+ secretion?
Inhibits pump
Decreases K+ channel permeability
Why does alkalotic filtrate increase K+ secretion?
Stimulates pump
Increases K+ channel permeability
How is K+ reabsorbed by intercalated cells?
Active process
H/K/ATPase in apical membrane
What can be affected by changes in neuromuscular excitability?
Cardiac conduction Pacemaker automaticity Neuronal function Skeletal muscle function Smooth muscle function
Give some causes of hyperkalaemia
Increases dietary intake (unlikely)
Inappropriate dose of IV K+ (dangerous)
Decreased renal excretion - AKI/CKI, ACEi, K+ sparing diuretics, low aldosterone
Internal shifts - DKA, cell lysis, acidosis, exercise
Describe the effects of hyperkalaemia
Altered excitability - depolarised cardiac tissue
More Na+ channels inactivated
Heart is less excitable
Arrythmias and heart block
What can happen to the GI tract in hyperkalaemia?
Paralytic ileus
What can occur on an ECG due to hyperkalaemia?
Tented T waves Prolonged PR interval ST depression No P wave Ventricular fibrillation
Describe the emergency treatment for hyperkalaemia
IV calcium gluconate (reduce effect on heart)
IV insulin and dextrose (K+ into cells)
Nebuliser beta agonists
(Dialysis to remove excess K+)
What is the long term treatment for hyperkalaemia?
Treat the cause
Reduce K+ intake
Measure to remove excess K+ (dialysis, K+ binding resins)
Give some causes of hypokalaemia
Diarrhoea, vomiting
Renal loss - diuretics, increased aldosterone
Metabolic alkalosis
Describe what happens to the heart in hypokalaemia
Hyperpolarised RMP
More Na+ channels in the active
Heart becomes more excitable
Arrhythmias
What are the ECG changes in hypokalaemia?
Low T wave
High U wave
Low ST segment
What is the treatment for hypokalaemia?
Treat the cause
K+ replacement (IV/oral)
(K+ sparing diuretics)
