Physio of the Adrenal Medulla

Question 1

What does the adrenal
1. Cortex
2. Medulla
produce? from what precursor?

Answer 1

1. Steroid hormones from the metabolism of cholesterol

2. Catecholamines from tyrosine

Question 2

Corticomedullary portal system

Answer 2

Allows vascular communication between the cortex and the medulla
Plexus arteries penetrate the cortex as do capillaries draining the cortical cells

Question 3

Cells of the adrenal medulla are called….

Answer 3

Chromaffin cells

(or pheochromocytes)

Question 4

Innervation of the adrenal gland

Answer 4

Sympathetic innervation
Preganglionic neuron synapses directly onto the chromaffin cells (nAChR)
Those cells then release EPI into the circulation

Question 5

4 places where catecholamines are synthesized

Answer 5

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)

Question 6

2 sources of tyrosine

Answer 6

Diet

Derived from phenylalanine (liver)

Question 7

Enzyme responsible for the rate limiting step when synthesizing catecholamines

Answer 7

Tyrosine hydroxylase

Question 8

2 key enzymes involved in catecholamine metabolism

Answer 8

Monoamine oxidase (expressed in catecholamine synthesizing cells)
Catechol-O-methyltransferase (expressed in other tissues)

Question 9

Do catecholamines bind to cell surface or intracellular receptors?

Answer 9

Cell surface (GPCRs)

Question 10

3 catecholamine receptors

Answer 10

DA receptor (D1, D2)
Alpha adrenergic receptor (a1 or a2)
Beta adrenergic receptor (B1, B2, B3)

Question 11

D1 receptors

Answer 11

Stimulatory (Gas)
Expression: cerebral, renal, mesenteric, and coronary vasculatures
Stimulation causes vasodilation in vascular beds

Question 12

D2 receptors

Answer 12

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

Question 13

3 places where the a1 and a2 adrenergic receptors work

Answer 13

Heart, vessels, SMC

a1 is stimulatory, a2 is inhibitory

Question 14

Where does
1. B1
2. B2
3. B3
receptors work?

Answer 14

1. Heart, kidney
2. Heart, lungs, vessels, kidney, liver
3. Heart, adipose tissue

Question 15

a1 receptors

Answer 15

Stimulatory (Gaq)
Expression: post-synaptic receptor
Mediates vascular and smooth muscle contraction
Stimulation causes vasoconstriction, increased systemic resistance, and increased BP

Question 16

Do
1. Alpha
2. Beta
bind NE or EPI more?

Answer 16

1. NE

2. EPI

Question 17

a2 receptors

Answer 17

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

Question 18

B1 receptors

Answer 18

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

Question 19

B2 receptors

Answer 19

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

Question 20

B3 receptor

Answer 20

Stimulatory (Gas)
Regulates energy expenditure
Lipolysis in white adipocytes
Thermogenesis in adipocytes

Question 21

What is the key stimuli for catecholamine production/secretion?

Answer 21

Stress
Can be physiological (hypoglycemia, low BP, etc), psychogenic (emotional distress, pain, trauma), or endocrine stimulation (AII, GCs)