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Catecholamines

The document discusses catecholamines such as epinephrine, norepinephrine, and dopamine that are produced in the adrenal medulla in response to stress. These catecholamines act on alpha and beta adrenergic receptors to prepare the body for emergency situations by increasing metabolic rate, heart rate, and blood pressure through various cardiovascular and metabolic effects. The adrenal medulla is innervated by preganglionic nerves and stimulated to secrete catecholamines. Glucocorticoids are necessary for normal development of the adrenal medulla. Catecholamines are metabolized to vanillylmandelic acid which is excreted in urine. Pheochromocytoma is a tumor

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• Epinephrine • Norepinephrine • Dopamine • Adrenaline • Noradrenaline act on alpha and beta adrenergic receptors Catecholamines
• Prepare individual deal with emergency situations.
Adrenal Medulla • A sympathetic ganglion • Post ganglionic neurones have lost their axons and become secretory cells • Stimulated by preganglionic nerves reaching gland via splanchnic nerves
• Glucocorticoid concentration is high in blood draining from cortex to medulla/ • After hyophysectomy glucocorticoid secretion of blood falls. • Glucocorticoids necessary for normal development of adrenal medulla. • In 21 b-hydoxylase deficiency, glucocorticoid secretion is reduced during fetal life. • In untreated b-hydoxylase deficiency, circulating catecholemines are low after birth.
Adrenal medulla Preganglionic neuron Acetyl choline Epinephrine 80% Norepinephrine 20%
PHYSIOLOGIC ACTIONS
Metabolic • Norephinephrine and ephinephrine: • Increase glycogenoliysis in liver and skeletal muscle. • Increase insulin by ẞ receptors. Decrease insulin by α- adrenergic receptors. • Mobilization of FFA • Increase plasma lactate • Stimulation of metabolic rare • Brought about by actions of α and ẞ adrenergic receptors.
• The initial rise in metabolic rate due to cutaneous vasoconstriction  decreases heat loss and leads to rise in body temperature  increased muscular activity. • Second rise is due to oxidation of lactate in liver.
• increase the force and rate of contraction of the isolated heart. mediated via β1 receptors. • Cardiac muscle. SA node • force rate • Increase myocardial contractility • May cause extra-systoles and arrythmias. Cardiovascular
• Norepinephrine - vasoconstriction in most if not all organs via α receptors. • Increase total peripheral resistance increase . • but epinephrine dilates the blood vessels in skeletal muscle and the liver via β receptors. • Decrease total peripheral resistance.
Norepinephrine Epinephrine increases the systolic blood pressure force of contraction increases the systolic blood pressure force of contraction Increases total peripheral resistance decreases total peripheral resistance increases diastolic blood pressure decreases diastolic blood pressure
Carbohydrate metabolism increase blood glucose level by glycogenolysis Epinephrine and norepinephrine both cause glycogenolysis. Fat metabolism mobilization of FFA from adipose tissue Sphincters contraction GIT, Urinary bladder Smooth muscles Relaxation Uterus Bronchioles
K+ • Epinephrine and norephinephrine cause an initial rise in plasma K+ because release of K+ from the liver • and then a prolonged fall in plasma K+ because of an increase entry of K+ into skeletal muscle that is mediated by B- adrenergic receptors.
• Physiologic stimuli affects adrenal medullary secretion through the nervous system. • Secretion is reduced in sleep. • Increased in emergency situation • During stress • Prepare body for fight or flight • Exposure to cold • Hypoglycemia Regulation of secretion
DOPAMINE • Renal and mesentry vasodialation by dopaminergic receptor. • Everywhere else, vasodialation by releasing norephinephrine. • Postive inotropic effect on heart by action of β receptors. • Increase the systolic blood pressure. • Does not affect the diastolic blood. • Used in treatment of traumatic and cardiogenic shock. • Causes natriuresis, inhibit Na, K, ATPase. • Deficiency in basal ganglia cause PARKINSONISM
• Methylated & oxydized to VMA vanillylmandelic acid excreted in urine. • Epinephrine and norepinephrine are metabolized by oxidation and methylation. The former reaction is catalyzed by MAO and the latter by catechol -O -methyltransferase (COMT • After many steps • vanillyl- mandelic acid (VMA) Metabolism
• Cause-tumour in cells of adrenal medulla so catecholamine secretion increase. • Signs and symptoms-Headache Tachycardia, Palpitation Hyperglycaemia Glucosuria Anxiety Pheochromocytoma