Circulating adrenaline and noradrenaline
Postganglionic · α1 α2 β1 β2 β3 Adrenaline 80%
The hormonal arm of the sympathetic system. Adrenaline released into the adrenal vein reaches every adrenoceptor within a circulation time, including β2 receptors in bronchial smooth muscle, skeletal muscle arterioles and liver that receive little or no direct sympathetic innervation.
Traced from the start
- Sympathetic (thoracolumbar) outflow
- Intermediolateral cell column T1–L2 via white rami communicantes
- Adrenal medulla
- Circulating adrenaline and noradrenaline
Detail
- Metabolic effects
- β2 hepatic glycogenolysis and gluconeogenesis; β3 (and β1) lipolysis; α2 inhibits and β2 stimulates insulin release; hypokalaemia from β2 Na+/K+-ATPase activation
- Vascular effects
- α1 constriction of skin and splanchnic beds; β2 dilatation of skeletal muscle and coronary arterioles — low-dose adrenaline lowers diastolic pressure
- Respiratory effects
- β2 bronchodilatation and stabilisation of mast cells — the main dilator input to human airways, which have sparse direct sympathetic nerves
When it goes wrong
Anaphylaxis with hypotension, angio-oedema and bronchospasm
Adrenaline 0.5 mg IM (1:1000, 0.01 mg/kg in children): α1 reverses vasodilatation and oedema, β2 opens airways and reduces mediator release, β1 supports cardiac output
Hypoglycaemia in a patient taking a non-selective β-blocker
Tremor and palpitations are masked but sweating persists, because sudomotor fibres are cholinergic — sweating may be the only warning
Practise this structure
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