Endocrinology 4

Endocrinology 4 - Endocrinology After Exam Three Adrenal...

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Endocrinology After Exam Three Adrenal glands Outer adrenal cortex Inner adrenal medulla Inner adrenal medulla innervated by sympathetic fibers and is considered part of the nervous system Adrenal medulla—post-ganglionic structure Cells in the medulla called chromaffin cells (pheochromocytes) express nicotinic cholinergic receptors Pre-ganglionic sympathetic fibers (release Ach as the neurotransmitter) ACh binds to the nicotinic receptors to stimulate the production and activation of an enzyme call tyrosine hydroxylase Chromaffin cells synthesize the catecholamines ( Epi and N-Epi) biogenic amine hormones synthesize from amino acid tyrosine Then converted into Dopa with tyrosine hydroxylase (rate limiting step) DOPA= dihydroxyphenylalanine Converted into dopamine with dopadecarboxylase converted into N-Epi with dopamine hydroxylase converted to Epi with PNMT (phenylethanolamine N-methyl transferase) activated by cortisol Dopamine, Epi, N-Epi---- Catecholamines made Might have encountered these as neurotransmitters released at the synaptic cleft N-Epi and Dopamine released into extracellular fluid= hormones Epi tends to be a hormone Catecholamines are short acting hormones (short half lives) Rate of release is matched by rate of inactivation Catecholamines(cat.) inactivated by two enzymes- 1) monoamine oxidase (MAO) 2) catechol-O-methyltransferase(COMT) Stimuli for release of cat. 1. Hypoglycemina 2. Stress—physical stress such as physical trauma, surgery, excessive exercise Cat. are responsible for the “fight or flight” response confrontation, one fights or fleas the threatening situation Energy is required Biological actions of cat.
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Binds to receptors called adrenergic receptors (heterogenous group receptors) 2 main adrenergic receptors alpha and beta Subtypes—alpha 1 and alpha 2, beta1 beta2 and beta3 Alpha 1—cat. Bind to alpha 1 adrenergic receptors= dissociation of G(q)alpha (PIP mechanism) Alpha 2—same with alpha 2 receptors= dissociation of G(I) alpha (inhibit cAMP activation) Beta1,2,3--- cat. Bind to cause dissociation of G(s)alpha= cAMP dept. mechanism 1. Smooth muscle in the walls of blood vessels (vascular smooth muscle) catecholamines binds to A1 receptors on the smooth muscle cells in the walls of blood vessels to stimulate vasoconstriction= increased TPR= increased BP 2. In the smooth muscle of blood vessels supplying skeletal muscles, catecholamines bind to A2 and B2 receptors to cause vasodilation increases blood flow to skeletal muscle to deliver oxygen/glucose into skeletal muscle for flight or flight response energy is required 3. Al receptors in the smooth muscle cells in the walls of the GI tract. Catecholamines bind to A1 receptors to cause contraction of the smooth muscle in the walls of the GI tract slow down motility and digestion. In the fight or flight response, most of the blood is diverted from the splanchnic circulation(supplying blood to the GI tract) to
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This document was uploaded on 10/27/2011 for the course BSCI 447 at Maryland.

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Endocrinology 4 - Endocrinology After Exam Three Adrenal...

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