catecholamines Flashcards
where are epinephrine and noreprinephrine produced
in the adrenal medulla
describe how epinephrine and noreprinephrine are synthesized
- beings with the amino acid tyrosine
- converted to dihydroxyphenylalanine
- catayzed to tyrosine hydroxylase (rate limiting step)
- converted to dopamine then noreprinephine then eprinephrine
is adrenaline a water soluble or lipid soluble hormone.
water soluble - needs to have a short half life and wok quickly (doesnt need transport proteins)
where does epinephrine come from
- all of the epinephrine in the blood comes from the adrenal medulla
where does noreprinephrine come from
- adrenal medulla
- postganglionic sympathetic neurons
explain why continual secretion of adrenaline is important for sympathetic tone
- continuous release of adrenaline from adrenals allows for modification of sympathetic tone. for example, continual secretion of adrenaline keeps the arterioles constricted to a 50% diameter so that in case of increased tone they can constrict more or in decreased tone they can relax more
explain the kinetics of catecholamines
- stored in secretory vesicles
- release via exocytosis
- circulate freely in the blood
- metabolised by liver and kidneys
- very short plasma half life (1-3 minutes)
- urinary excretion of unmetabolised epinephrine and norepinephrine
explain the relationship between the nervous system and the adrenal medulla
- pre ganglionic sympathetic neurons carry action potential to adrenal medulla
- adrenal acts as sympathetic ganglion and is equivalent to a post ganglionic sympathetic neuron
neurons that secrete acetylcholine are
cholinergic
- neruons with cell bodies in the CNS are generally cholinergic
neurons that secrete norepinephrine are
adrenergic
- post sympathetic neurons are adrenergic
what are th receptors types of adrenergic receptors
alpha 1/2 and beta 1/2
some cells can have both
what do alpha 1 receptors do
- vasconstrction
- pupil dilation
- intestinal relaxation
- pilomotor contraction
- bladder spincter contraction
what do beta 2 receptors do
- vasodilation
- bronchodilation
- glycogenolysis
- lipolysis
what do B2 receptors do
- vasodilation
- bronchodilation
- glycogenolysis
- lipolysis
what do stimulated alpha 2 receptors do
- sedation and anaesthesi
describe typical signal transduction of catecholamines
- bind to receptors
- activate second messengers
- often G protein coupled
- multiple pathways from here: adenyl cyclase, phospholipase C, IP3 and DAG
- Ion channels
wht are the metabolic effects of catecholamines
idea is to increase the amount of readily availible energy substrates
- mobilise glucose
- mobilise fatty acids
thus brain functions optimally and muscles can carry animal away from danger
- increase glycogenolysis
- and gluconeogenesis
animals that are stress will show what on blood work, why?
- hyperglycemia
- because epinephrine has optimised glucose use and glycolysis/gluconeogenesis in the body
what is the importance of medullary epinephrine
- metabolic stimulus (epinephrine has 5-10x greater metabolic effect than noreprinephrine
- epinephrine has greater effect on beta receptors
- epinephrine acts on beta 2 receptos causing vasodilation while noreprinephrine acts on alpha receptrs causing vasoconstriction
why are noreprinephrin and epinephrine important but different in function
- noreprinephrine has a more profound effect on blood vessels while epi has more effect on heart
- one raises blood pressure, other raised cardiac output
- important to have different sources for these
