Adrenal Medulla Flashcards
What are the adrenomedullary hormones?
Norepinephrine and Epinephrine
What is the percentages of andrenomedullary hormones?
90% Epi, 10% NE
The adrenal medulla is part of what nervous system?
Sympathetic Nervous System
What is the functional unit of the adrenal medulla? What do they function as?
Chromaffin Cells; Post-ganglionic nerves that secrete Epi and NE into the blood
How are the chromaffin cells stimulated?
Chromaffin cells are directly stimulated by ACTH released from sympathetic preganglionic fibers (splanchnic nerve); Chromaffin cells synthesize/secrete Epi/NE directly into the blood and is carried to various organs in the body
What are chromaffin granules?
storage and secretory granules for Epi and NE and play a major role in their synthesis
What is the rate-limiting step in Epi synthesis?
Tyrosine –> DOPA (by Tyrosine hydroxylase)
What enzyme converts Epi into NE? What stimulates this enzyme?
PNMT; Cortisol
What is one chromaffin granule that converts dopamine to NE?
Dopamine B-hydroxylase
What are the physiologic factors for synthesis and secretion of Epi/NE? (6)
(1) Anxiety
(2) Pain
(3) Trauma
(4) Hypovolemia
(5) Hypoglycemia
(6) Hypothemia
What does Chromogranin do?
It is a secretory peptide
What is VMAT? What does it do?
Vesicular Monoamine Transporter; moves Epi into the secretory vesicles that are released into the synapse
What is the negative feedback process by Epi and NE?
They negatively feedback Tyrosine Hydroxylase to stop the synthesis of more catecholamines
Acute regulation increases ACTIVITY/SYNTHESIS of TH?
ACTIVITY
Chronic regulation increases ACTIVITY/SYNTHESIS of TH?
BOTH
In chronic regulation, what else is secreted into the Chromaffin cell? What does it do?
Cortisol; it increases activity of PNMT to convert NE to EPI
What are circulating blood levels of EPI, NE at basal and stimulated?
EPI (adrenal medulla)- Basal 20-50 pg/ml, Stimulated >250 pg/ml; NE (sympathetic nerves)- Basal 100-200 pg/ml; Stimulated >1000 pg/ml
What is the half life of Epi/NE?
1-3 minutes
T/F Epi/NE is carried in the plasma in free form
TRUE; there is no binding protein
What are the major sites of Epi and NE metabolism?
Liver, Kidney, and Sympathetic nerve endings
Epi and NE are acted up by what enzymes?
Catechol-O-Methyl Tranferase and Monoamine Oxidase
What are inactive metabolites that form by the actions of the enzymes? Where are they excreted?
VMA, Metanephrine (EPI), Normetanephrine (NE); secreted in the urine
What are the catecholamine receptors?
Adrenergic receptors; Alpha and Beta
Which has the greatest effect on Epi than NE?
B-2
