Lecture 7

• During the fight-or-flight response, the sympathetic nervous system activates both the cardiovascular and the adrenal catecholaminergic systems for rapid homeostatic adjustments to a threat.
• The adrenal gland secretes catecholamines which cause rapid changes in heart rate and the mobilization of stored fuels to provide energy to skeletal muscle and to the brain.
• The adrenal medulla produces catecholamines.
• The catecholamines include epinephrine and norepinephrine.
• Epinephrine is the major product of the medulla in many mammalian species.
• Norepinephrine is the minor product of the adrenal medulla but is the major neurotransmitter of the sympathetic nervous system.
• Cortisol induces expression of the enzyme PNMT which converts epinephrine to norepinephrine.
• The fight-or-flight response is triggered by the activation of the sympathetic nervous system.
• Catecholamines are stored in chromaffin cells of the adrenal medulla.
• Catecholamine secretion increases with exercise or stressful stimuli due to the release of acetylcholine.
• Increased epinephrine in response to stressful stimuli accelerates heartbeat, causes piloerection, and dilates pupils.
• Catecholamines bind to albumin with low affinity but high capacity.
• Catecholamines are inactivated rapidly and have a relatively low affinity for their receptors.
• Catecholamines are metabolized by MAO produced at nerve endings.
• Sympathetic endings in the medulla largely take up catecholamines.
• Alpha adrenergic receptors largely function in norepinephrine signaling in the sympathetic nervous system.
• Physiological Effects of Catecholamines:

  1. Cardiovascular- activated rapidly. Increased HR, vasodilation, venoconstriction, glycogen mobilization.
  2. Carbohydrate metabolism-
  3. Thermogenic -