Sympathetic Nervous System by MikeJenny


									            Adrenal Medulla &
         Sympathetic Nervous System
Porterfield Chapter pp 131-137

     Adrenal Medulla and Sympathetic Nervous System
     Catecholamine Synthesis
     Adrenergic Receptor Subtypes
     Regulation of Release
     Physiological Effects
     Comparison – Sympathoadrenal and Sympathetic Nervous

   Sympathetic Nervous System
– Adrenergic branch of autonomic nervous system
– First line of defense in responding to stress
   – Two branches
• 1) SNS - preganglionic cholinergic nerve endings synapse with
postganglionic adrenergic neurons
• 2) Sympathoadrenal System - preganglionic cholinergic nerve
endings synapse with postganglionic chromaffin cells (located in
adrenal medulla).
   Sympathetic response
– Extremely rapidly activated
– Responds to wide variety of stressors
– Uniquely tailored
• Individual components of both branches can be recruited singly
or in any combination.

Anatomy of the adrenal gland

– Epinephrine and Norepinehrine &Dopamine (very little)

– Site of epinephrine synthesis:
– Adrenal medulla
– Chromaffin cells (neuroendocrine cells)
– Epinephrine:
– Adrenal medulla - sole source of epinephrine in circulation
– 85% of medullary output
– Hydrophilic
Catecholamines in circulation (hydrophilic)
EPINEPHRINE                          NOREPINEPHRINE
All from adrenal medulla             Most from sympathetic

Approx 50% bound to                  Approx 50% bound to
albumin                              albumin

Levels = 20-50 ng/ml                 100-350 ng/ml
t½ < 10 seconds                      t½ < 15 seconds
SNS and adrenal medulla innervation

Synthesis of catecholamines
Chromaffin cell

Catecholamine Synthesis:
– Tyrosine hydroxylase
– Rate limiting step
– All intermediate products       negative feedback on tyrosine
– PNMT: Only in CNS and adrenal medulla
– Required for synthesis of epinephrine

Sympathetic Response
– J. Tepperman - “The sympathetic nervous system and adrenal
  medulla respond to differing physiological challenges by
  selective recruitment of subsystems as determined by site of
  release and receptor availability---
– All 88 keys on a piano are not struck at once; rather chords
  appropriate to the musical piece are played.”

Adrenergic Receptor Subtypes

Adrenergic Receptor Types (in general)
– Alpha
– Mostly mediated by NE (from SNS nerve endings)
– Constrictive events
– Excitatory events
– Beta
– Mostly mediated by E (from adrenal medulla)
– Dilatory events
– Relaxation events

Regulation of Release Sympathetic, Cholinergic Stimulus
– 1) Decreased blood pressure:
– In hemorrhage (need blood pressure stability)
– 2) Decreased blood glucose:                      NE & E
– Need energy mobilization
– 3) Decreased oxygen availability:
– Need + bronchodilation

4) Stress / Anxiety: (E/NE)

– Need + energy, + cardiac output, +blood to essential tissues
– 5) Cold:
– Need to + metabolism to conserve heat
6) Exercise:                                                      E
– Need to + oxygen and + blood to muscle,
+ energy mobilization
– 7) Postural hypotension:
– Need to + cardiac output when standing
Physiological Effects
“Fight or Flight”
The sympathetic response involves 〈and ® receptors working in
concert to increase delivery of O2 and energy sources to critical
body compartments for mobilization of energy.
   Sympathetic Response “Fight or Flight”
Tissue Direct           Response              Physiological
Lungs                   ↑ respiration         ↑O 2 to heart

Heart                  ↑ cardiac               ↑ blood/O 2
                       output                  to tissues
Vascular               +/- regional            Preferential shunting
Smooth                 blood flow              of
Muscle                                         blood
Skeletal               ↑ contraction           ↑ locomotion

Liver                  ↑glycogenolysis         ↑ glucose to

Adipose Tissue         ↑ lipolysis             ↑FFA to tissues

〈/® Receptors
Cardiovascular System
   ®1 Receptors
– Cardiac muscle contr. ↑ Cardiac output
   〈1/〈2 Receptors
– Vasoconstriction ↑ Peripheral resist.
* Skin, kidney, mucosa, G.I. tract
   ®2 Receptors
– vasodilation −− Peripheral resist.
* Heart, skeletal muscle, bronchial smooth muscle
* blood pressure = no change
α/β Receptors Working Together
   Specialized Smooth Muscle - Urinary Bladder
  β2 Receptor
– Non-sphincteric muscle
– Relaxation
 α2 Receptor
– Sphincter muscle
– Constriction

  Pathophysiology :Adrenal Medulla
 – Not a serious physiological problem
– SNS compensates for cardiovascular regulation
– Other counter-regulatory hormones compensate for metabolic
• Glucagon, GH, cortisol

Pathophysiology: Adrenal Medulla
   Hypersecretion - ↑ ↑ E/NE
– Pheochromocytoma - beign tumor (fatal if untreated because of

• Severe hypertension
• Paroxysmal episodes – tachycardia, anxiety, headache, tremor,
• Severe damage to vascular cells (↑ ↑ Ca2+)
– Neuroblastoma – malignant tumor
• Same symptoms as above only more severe

Study questions:

   1- Identify the chemical nature and mechanism of action of catecholamines and their
      metabolic fate?
   2- Describe the biologic consequences of adrenal medullary activation and identify
      the target organs or tissues for catecholamine effects along with the receptor
      subtype that mediates the responses?
   3- Identify diseases caused by oversecretion of adrenal catechoamines?


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