Catecholamines Flashcards
Label the adrenal gland
What is the secretion of the adrenal medulla?
catecholamines:
- epinephrine/adrenaline
- norepinephrine/noradrenaline
Describe the synthesis of epinephrine and norepinephrine
What are the sources of epinephrine and norepinephrine
Epinephrine - adrenal medulla
Norepinephrine - adrenal medulla + postganglionic sympathetic neurons
Describe the sympathetic control of catecholamine secretion
Sympathetic tone keeps arterioles constricted to 50% diameter
Increased sympathetic stimulation: more constriction
Decreased sympathetic stimulation: less constriction
Describe the effect of resting catecholamine secretion from adrenal medulla
Sufficient to maintain blood pressure if nervous system lost
Dominant mechanism for maintaining vascular tone
Describe the kinetics of catecholamines
Stored in secretory vesicles and released via exocytosis
Circulate freely in blood
Metabolised by liver and kidneys
Short plasma half-life (1-3 mins)
Urinary excretion of unmetabolised catecholamines
Describe the effect of catecholamines compared to sympathetic stimulation
Catecholamines have same effect as direct stimulation via sympathetic nerves - but have effect on whole body simultaneously and has a longer lasting effect
Describe neurone classification by transmitter
Adrenergic neurones - secrete norepinephrine (post-ganglionic sympathetic neurones)
Cholinergic neurones - secrete acetylcholine (parasympathetic or somatic)
Describe the interaction between the SNS and adrenal medulla
Adrenal medulla acts as a sympathetic ganglion
Pre-ganglionic sympathetic neurons carry action potential to adrenal medulla => influx of Ca2+ => exocytosis of catecholamines
What are the effect of catecholamines binding to alpha 1 adrenergic receptors?
Vasoconstriction
Pupil dilation
Intestinal relaxation
Pilomotor contraction (erects hairs)
Bladder sphincter contraction
What is the effect of catecholamines binding to alpha 2 adrenergic receptors?
sedation and anaesthesia
What is the effect of catecholamines binding to beta 1 adrenergic receptors
Increase HR
Increase contractility
What is the effect of catecholamine binding to beta 2 receptors
Vasodilation
Bronchodilation
Glycogenolysis
Lipolysis
Describe the action of alpha-2 adrenergic receptors in sedation and anaesthesia
Often has re-synaptic position and exerts a negative feedback effect on synaptic signal transmission
What are the clinical consequences of SNS activation?
Describe the adenylyl cyclase pathway in B-adrenergic receptors
Catecholamine binds to cell surface receptor => activates G protein => stimulated adenylyl cyclase => generates cyclic AMP (cAMP) => activates protein kinase A => phosphorylates protein => biological response
Describe the effects of cAMP
Binds to protein kinase A and enters nucleus
binds to CREB (cAMP-response element binding protein) and phosphorylates it => CREB-P
CREB-P binds to CRE and changes gene expression
Describe the phospholipase C pathway in alpha adrenergic receptors
Hormone binds cell surface receptor
Activates phospholipase C via G protein
Phospholipid PIP2 broken down to IP3 and DAG
DAG activates protein kinase C which phosphorylates protein => biological response
What factors effect the tissue response to SNS activation
Type and density of receptors
Relative concentrations of local catecholamines
Give an example of how different adrenergic receptors cause different responses upon sympathetic stimulation
Alpha receptors in intestine => vasoconstriction
Beta 2 receptors in muscle => vasodilation
What are the metabolic effects of catecholamines?
Glycogenolysis and gluconeogenesis to increase amount of readily available energy
Stimulates hormone-sensitive lipase => lipolysis
What is the clinical relevance of the metabolic effects of catecholamines?
Stressed animals show hyperglycaemia
Compare the effects of epinephrine and noreinephrine
Epinephrine:
- greater metabolic effect
- greater effect on B-receptors (cardiac stimulation)
- causes vasodilation via B2 receptors (fight or flight)
Norepinephrine:
- causes vasoconstriction via alpha receptors (shock)
