Adrenaline
Site of Production
- adrenaline secreted from chromaffin cells (stain with chromate)
- produced in adrenal medulla
Synthesis
- adrenaline synthesised from noradrenaline by
phenylethanolamine-N-methyltransferase (PNMT)
- PNMT synthesis induced by cortisol
- synthesis regulated by rate limiting enzyme (tyrosine hydroxylase)
Stimulus
- preganglionic fibres of Sympathetic
Nervous system release acetylcholine onto chromaffin cell, this causes
membrane depolarisation and vesicle release.
Termination of Effect
- catecholamines removed by:
- reuptake by cells
- uptake of receptors on target cells
- liver metablism by catecholamine-O-transferase and MAO
Effects
- a-receptors cause
- vasoconstriction
- iris dilation
- intestinal relaxation
- intestinal sphincter contraction
- pilomotor contraction
- bladder sphincter contraction
- b1 receptors cause
- cardioacceleration
- increased myocardial strength
- lipolysis
- b2 receptors cause
- vasodilation
- intestinal relaxation
- uterus relaxation
- bronchodilation
- calorigenesis
- glycogenolysis
- bladder wall relaxation
Disorders
14.4.1 Adrenal Medulla
| synthesis of adrenaline and noradrenaline; storage in
chromaffin granules |
|
| catecholamine receptors and their distribution in tissues
(see 6.6.2.2) |
|
| actions on cardiovascular system, respiratory system,
gastrointestinal tract, metabolism |
|
| control by autonomic nervous system |
|
| dysfunction: effects of phaeochromocytoma |
|
|