Flashcards in Potassium Control Deck (32)
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1
What is the approximate ICF conc for K+?
120-150 mmol/L
2
What is the approx ECF conc of K+?
3.5 - 5 mmol/L
3
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
4
Give some examples of potassium rich food
Banana
Honey dew melon
Raisins
Orange
Tomato
Baked potatoes
5
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
6
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
7
What factors increase K+ uptake into cells?
Hormones - insulin, aldosterone, catecholamines
Increased potassium in ECF (concentration gradient)
Alkalosis (shift of H+ out, K+ in)
8
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)
9
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
10
How do aldosterone and K+ affect each other?
K+ in blood stimulates aldosterone secretion
Stimulates uptake of K+ via Na/K/ATPase
11
How do catecholamines affect K+ uptake?
Act via beta 2 adrenoceptors
Stimulate Na/K/ATPase
Increases cellular uptake of K+
12
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
13
How is dangerous hyperkalaemia prevented in exercise?
Uptake of K+ by non-contraction tissue
Increase catecholamines to increase K+ uptake into other cells
14
In terms of K+, acidosis leads to ...
Hyperkalaemia
15
In terms of K+, alkalosis leads to...
Hypokalaemia
16
Where and how in the nephron is K+ reabsorbed?
PCT - passive, paracellular
TAL - active, NKCC2
DCT/CD - intercalated cells
17
Which cells secrete K+ into the nephron lumen?
Principal cells of DCT and cortical collecting duct
18
How does aldosterone promote K+ secretion in the kidney?
Increases transcription of the relevant proteins
Na/K/ATPase
K+ channels
ENaC
19
Why does acidic filtrate decrease K+ secretion?
Inhibits pump
Decreases K+ channel permeability
20
Why does alkalotic filtrate increase K+ secretion?
Stimulates pump
Increases K+ channel permeability
21
How is K+ reabsorbed by intercalated cells?
Active process
H/K/ATPase in apical membrane
22
What can be affected by changes in neuromuscular excitability?
Cardiac conduction
Pacemaker automaticity
Neuronal function
Skeletal muscle function
Smooth muscle function
23
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
24
Describe the effects of hyperkalaemia
Altered excitability - depolarised cardiac tissue
More Na+ channels inactivated
Heart is less excitable
Arrythmias and heart block
25
What can happen to the GI tract in hyperkalaemia?
Paralytic ileus
26
What can occur on an ECG due to hyperkalaemia?
Tented T waves
Prolonged PR interval
ST depression
No P wave
Ventricular fibrillation
27
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+)
28
What is the long term treatment for hyperkalaemia?
Treat the cause
Reduce K+ intake
Measure to remove excess K+ (dialysis, K+ binding resins)
29
Give some causes of hypokalaemia
Diarrhoea, vomiting
Renal loss - diuretics, increased aldosterone
Metabolic alkalosis
30
