The Adrenergic System Flashcards
neurotransmitters of the adrenergic system are
catecholamines -
adrenaline and noradrenaline.
catecholamines -
adrenaline and noradrenaline.
( physiology - mechanism )
+ look the steps from pic of atlas
1) - They are synthesized in the cytoplasm of cells adrenergic neurons from tyrosine which converts in dopa (by tyrosine hydroxilase ) , an amino acid which then transforms into dopamine. ( tyrosine -> DOPA -> DOPAMINE )
2) Dopamine -> NE (noradrenaline) which
is converted into -> epinephrine (adrenaline).
3) Catecholamines are released from the deposit granules by exocytosis.
4) From the synaptic cleft it diffuses and stimulate specific receptors - adrenergic receptors.
5) Termination of the effect of catecholamines is done by passive diffusion,
reuptake and metabolism by 2 enzymes - monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT)
Sympathomimetics
Agents that activate adrenergic receptors
Sympatholytics
Agents that blocks the activation of adrenergic receptors
Adrenergic receptors
G protein coupled receptors and are of two
types - α and β.
α-adrenergic receptors:
- postsynaptic α1 receptors
- presynaptic, postsynaptic and extrasinaptic α2 receptors.
adrenergic receptors G coupled + production of 2nd messenger
α1 receptors are coupled with Gq proteins. -> ACTIVATES : phospholipase C , producing IP3 & DAG
α2 receptors are coupled with Gi proteins -> INHIBIT : adenyl cyclase , decreasing cAMP formation
β-adrenergic receptors are coupled with Gs proteins -> STIMULATE : Adenyl cyclase with an increase in intracellular cAMP
β-adrenergic receptors -
β1, β2, β3
Effects of adrenergic receptor stimulation
α1 receptors: (6)
VASCULAR LEVEL : o vasoconstriction, (thus ↑BP); o decreased bronchial secretion , o mydriasis, GI LEVEL : o spleen capsule contraction, o piloerection, o decreased insulin secretion.
presynaptic α2 receptors:
decreases the release of norepinephrine into the synaptic cleft -
feedback mechanism. ( negative feedback)
- inhibition of neurotransmitter release ( noradrenaline + acetylcholine )
α2 postsynaptic receptors:
Vasoconstriction
extrasynaptic α2 receptors:
o stimulates platelet aggregation
+ contraction of vascular smooth muscles
+ inhibition of insulin release
β1 receptors:
increases the activity of the heart (increases contractility, A-V conduction, excitability)
o stimulates renin secretion
- CNS = anxiety
β2 receptors:
o vasodilation, ( in skeletal muscle ) o bronchodilation, o relaxes uterine muscles, o tremor, o agitation, o nervousness, o increases gluconeogenesis and glycogenolysis, o increases insulin secretion
β3 receptors:
o lipolysis and glycogenolysis.