Adrenal Medulla

Dr.Yogesh Kumar

Department Of Physiology

Adrenal Medulla The adrenal medulla, which constitutes 28%

of the mass of the adrenal gland, is made up of interlacing cords of densely innervated granule-containing cells that abut on venous sinuses

Made of chromaffin cells – 2 types Contains granules - 2 types Paraganglia cells

The adrenal medulla is in effect a sympathetic ganglion

The cells secrete when stimulated by the preganglionic nerve fibers

Innervated by splanchnic nerves prepare the body for emergencies, the "fight-

or-flight" responses

Catecholamines Adrenalin (epinephrine) Noradrenalin (norepinephrine) Dopamine

Synthesis Of Catecholamines

Secretion Of Catecholamines

Fight or flight reactions Pre-ganglionic ativation Exo-cytosis of granules mediated by ca

influx Physiological and psychological stimuli such Pain , anxiety , trauma , hypovolemia ,

hypoglycemia , hypothermia, severe exercise , emotional stimulus

Metabolism

Table 1. Classification of Adrenergic Hormone Receptors

Receptor AgonistsSecond

MessengerG protein

alpha1 (1) E>NE IP3/Ca2+; DAG Gq

alpha2 (2) NE>E cyclic AMP Gi

beta1 (1) E=NE cyclic AMP Gs

beta2 (2) E>>NE cyclic AMP Gs

E = epinephrine; NE = norepinephrine

Alpha adrenergic receptors - NE ,E – major stimulatory (except intestine)

Beta adrenergic receptors - E – major inhibitory ( except myocardium)

Receptors

Alpha 1 , 2 Beta 1, 2 ,3 Up regulation Down regulation Adrenalin – alpha 1,2 . Beta 1, 2 ,3 Nor-adr – alpha 1,2 . Beta 1 , poor beta

activity

Actions Of Adrenal Medulla

Actions On Various Organs

Metabolism –o2 consumption co2 production

Carbohydrate Metabolism

Gluconeogenesis , glycogenolysis , glycogenesis , insulin inhibition , glucagon secretion , ACTH secretion

Lipid Metabolism – lipolysis thro’ HSL Heart - beta 1 Cns – alertness , anxiety , tremors - beta Blood vessel – blood pressure Respiration – beta 2

Contd Skin –arrector pili Urinary Bladder And GIT Eyes –alpha - pupilary dilation , beta produces relaxation of

ciliary muscle Blood – increases rbc , coagulability Skeletal muscle – contraction , increase blood supply ,

glycogeneolysis Smooth muscle - splenic capsule

shpincters

dilator pupillae

uterus

arrector pili

Contd Relaxation in non sphicteric gi muscles Urinary bladder Bronchioles Kidney – renin secretion Sweat glands Lacrmal glands Salaivary glands

Role In Secretion Of Other Hormones

Insulin , somatostatin Glucagon Thyroxin , t4 – t3 enhancement TRH Renin secretion

Regulation Acute sympathetic stimulation Chronic sympathetic stimulation ACTH – increases enzymes of catechol Cortisol - PNMT Epinephrine Exposure to cold Hypoglycemia

Dopamine Produced by adrenal medulla and

dopaminergic neurons Vasoconstriction Dilatation in mesentery Increase in heart rate and BP

Pheochromocytoma Endocrine hypertension Anxiety Chest pain Fever Headache Hyperglycemia Nausea and vomiting Polyuria , glucosuria Palpitations Sweating Tachycardia Wt loss Test for pheochromocytoma