MECH 430 Lecture Notes - Lecture 14: Tyrosine Hydroxylase, Adrenal Medulla, Preganglionic Nerve Fibers
9 Jun 2018
School
Department
Course
Professor
➢ Adrenal Medulla
o Total mass o the medulla is about 1 gram
o About 15% of total adrenal glands weight
o Responsible for producing norepinephrine and
epinephrine
o modified nervous tissue
o Adrenal medullar and paraganglia are part of the
autonomic/sympathetic nervous system
▪ i.e. not under conscious control
▪ coordinates “fight-flight” response to alarm by
increasing blood pressure and cardiac output &
dilating pupils
▪ not under conscious control, coordinates fight or flight response
o preganglionic neurons release acetylcholine to stimulate medulla cells to release hormones
▪ modified nervous cells
▪ coordinated response between the nervous system
and the adrenal medulla
o Interpreting signals from the environment → spinal cord →
preganglionic sympathetic neurons that innervate the
medullary area
▪ → stimulation for release of ACTH → combine
with receptors on the medullary cells → epinephrine
and norepinephrine are released into the blood
➢ Hormones of the Adrenal Medulla
o Cortisol required to enhance PNMT,
therefore less norepinephrine produced
and stored + PNMT also found in other
tissues (lung, kidney, pancreas)
▪ Recall blood flow → i.e. stress
increases cortisol, which
increases PNMT
o The catecholamines are often referred to
as adrenaline
o Dopamine → norepinephrine →
epinephrine
o Cortisol is required to induce this enzyme
(dopamine B-hydroxylase) → less
PNMT → less epinephrine
find more resources at oneclass.com
find more resources at oneclass.com
o Hormones is the adrenal medulla are released in response to appropriate stimuli
o 80% of released catecholamines are epinephrine
o 20% norepinephrine
➢ Synthesis and degradation of catecholamines
o Rate limiting step:
▪ Tyrosine hydroxylase
▪ Conversion of norepinephrine requires
glucocorticoids → provided by the cortical
capillaries
o ** metephinephrine → VMA - inactivated by monoamine
oxidase (MAO) and COMT (catechol-O-methyltransferase)
Pathways
o Similar pathway for degradation and inactivation
➢ Other hormones secretion by the adrenal medulla
o Granules also contain met-enkephalin and leu-
enkephalin (related to endorphins)
o They are co-excreted with the catecholamines
o Enkephalins may block neurotransmitters (similar to
morphine) and acts as an endogenous analgesics
▪ Ex: runners overcoming pain and being
euphoric
o Norepinephrine and epinephrine are stored in
granules, which are released upon stimulation
➢ Fight-or-flight Response
o Bozeman Biology:
▪ Epinephrine affects the Liver: converts glycogen to glucose (glycogenolysis) → glucose
is used as an energy supply
▪ Epinephrine affects the Lungs: increases breathing rate
▪ Epinephrine affects the Heart: increases the rate of the heart beat
▪ Epinephrine affects the GI: vasoconstriction (slows down digestion) → blood is moved to
other areas
▪ Slowest response is during the biosynthesis of steroids
▪ Compare acute vs. long-term vs. exhaustion phase
▪ Cortisol: slower response because it must be synthesized
▪ Medulla: faster response because already stored in granules
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Pnmt less epinephrine: hormones is the adrenal medulla are released in response to appropriate stimuli, 80% of released catecholamines are epinephrine, 20% norepinephrine. Synthesis and degradation of catecholamines: rate limiting step, tyrosine hydroxylase, conversion of norepinephrine requires glucocorticoids provided by the cortical capillaries, ** metephinephrine vma - inactivated by monoamine oxidase (mao) and comt (catechol-o-methyltransferase) Pathways: similar pathway for degradation and inactivation. Fight or flight acute response: these events are in preparation of the activity that is about to be experienced. Increases muscle glycogenolysis: rapidly mobilizes fatty acids as the primary fuel for muscle action, mobilizes glucose for the brain by hepatic glycogenolysis/gluconeogenesis, preserves glucose for cns by insulin release leading to reduced glucose uptake by muscle/adipose. Increases cardiac output: norepinephrine elicits responses of the cv system, blood flow, insulin secretion. Effects of catecholamines on organ systems: stress causes preganglionic fibers to release acetylcholine to stimulate medulla cells to release catecholamines. Differences between epinephrine and norepinephrine: epinephrine >> norepinephrine.
