Physio of the Adrenal Medulla Flashcards
What does the adrenal
1. Cortex
2. Medulla
produce? from what precursor?
- Steroid hormones from the metabolism of cholesterol
2. Catecholamines from tyrosine
Corticomedullary portal system
Allows vascular communication between the cortex and the medulla
Plexus arteries penetrate the cortex as do capillaries draining the cortical cells
Cells of the adrenal medulla are called….
Chromaffin cells
(or pheochromocytes)
Innervation of the adrenal gland
Sympathetic innervation
Preganglionic neuron synapses directly onto the chromaffin cells (nAChR)
Those cells then release EPI into the circulation
4 places where catecholamines are synthesized
Adrenal medulla (chromaffin cells)
Postganglionic neurons of the SNS
Noradrenergic and dopaminergic neurons of the CNS
Paraganglia of the periphery (collections of chromaffin cells outside the adrenal medulla)
2 sources of tyrosine
Diet
Derived from phenylalanine (liver)
Enzyme responsible for the rate limiting step when synthesizing catecholamines
Tyrosine hydroxylase
2 key enzymes involved in catecholamine metabolism
Monoamine oxidase (expressed in catecholamine synthesizing cells) Catechol-O-methyltransferase (expressed in other tissues)
Do catecholamines bind to cell surface or intracellular receptors?
Cell surface (GPCRs)
3 catecholamine receptors
DA receptor (D1, D2)
Alpha adrenergic receptor (a1 or a2)
Beta adrenergic receptor (B1, B2, B3)
D1 receptors
Stimulatory (Gas)
Expression: cerebral, renal, mesenteric, and coronary vasculatures
Stimulation causes vasodilation in vascular beds
D2 receptors
Inhibitory (Ga0/i)
Expression: pre and post synaptic, localized to sympathetic nerve endings, sympathetic ganglia, brain, and lactotrophs of the AP
Stimulation causes inhibition of NE release, inhibition of ganglionic transmission, and inhibition of PRL release
3 places where the a1 and a2 adrenergic receptors work
Heart, vessels, SMC
a1 is stimulatory, a2 is inhibitory
Where does 1. B1 2. B2 3. B3 receptors work?
- Heart, kidney
- Heart, lungs, vessels, kidney, liver
- Heart, adipose tissue
a1 receptors
Stimulatory (Gaq)
Expression: post-synaptic receptor
Mediates vascular and smooth muscle contraction
Stimulation causes vasoconstriction, increased systemic resistance, and increased BP
Do
1. Alpha
2. Beta
bind NE or EPI more?
- NE
2. EPI
a2 receptors
Inhibitory (Gai)
Expression: presynaptic sympathetic nerve endings and post synaptic tissues
Stimulations cause inhibition of NE release, down-regulates central symp outflow, and decreased BP
B1 receptors
Mediates cardiac effects and is more responsive to isoproterenol than to E/NE
Stimulation causes positive ionotropic and chronotropic effects on the heart, increased renin secretion in the kidney, lipolysis in adipocytes
B2 receptors
Stimulatory OR inhibitory (Gas or Gai)
Mediates: bronchial, vascular, and uterine smooth muscle relaxation
Stimulation causes: bronchodilation, vasodilation in skeletal muscle, glycogenolysis, and release of NE from symp nerve terminals
B3 receptor
Stimulatory (Gas)
Regulates energy expenditure
Lipolysis in white adipocytes
Thermogenesis in adipocytes
What is the key stimuli for catecholamine production/secretion?
Stress
Can be physiological (hypoglycemia, low BP, etc), psychogenic (emotional distress, pain, trauma), or endocrine stimulation (AII, GCs)
