Adrenal medulla

adrenal medulla

1. ADRENAL MEDULLA DILSHANA FATHIMA MSc . BIOCHEMISTRY

2. INTRODUCTION Adrenal glands are triangle shaped glands located on the top of the kidney. Each gland consists of a medulla surrounded by the cortex.

3. ADRENAL MEDULLA The inner region of adrenal gland. Is a modified sympathetic ganglion of Autonomic nervous system. Occupies central 20% of adrenal gland. Consists of rounded groups of relatively large & granular cells called chromaffin cells / pheochromocytes . Chromaffin cells contain granules composed of catecholamines , adenine nucleotides, proteins & lipids

4. Proteins of these granules is referred to as chromogranin . The human adrenal medulla consists of 2 types of cells Adrenalin (A) storing cells Nor adrenalin (N) storing cells One type of cells secrete adrenaline & the other type secrete nor epinephrine. These hormones are stored in the form of chromaffin granules. In human, 80% of chromaffin granules contain adrenalin & 20% of granules contain nor adrenaline.

5. SYNTHESIS OF HORMONES The pathway of catecholamine biosynthesis in CNS, sympathetic post ganglionic neurons & adrenal chromaffin tissue appear to be identical. The number of steps in each pathway however, depend on the definite product – dopamine(DA), adrenalin(E), nor adrenalin(NE)

6. Phenylalanine hydroxylase Tyrosine hydroxylase Dopa decarboxylase Dopamine β - hydroxylase Nor epinephrine N-methyl transferase Epinephrine

7. STORAGE & RELEASE Catecholamines are stored within granules wherein they are complexed with ATP & specific protein chromogrannin & DBH. The secretory vesicles are released through a stimulus-secretion coupling requiring calcium. All the contents are released during vesicular exocytosis .

8. DURATION OF ACTION The NE secreted directly into a tissue remain only for a few second, that its uptake & diffusion away from the tissues are rapid. The NE & E secreted into the blood remain active until they diffuse into some tissue, where they can be destoyed by catechol -O-methyl transferase , this occur mainly in liver. Therefore when secreted into blood, NE & E remain active for 10-30 sec

9. MECHANISM OF ACTION Action of E & NE are executed by binding with receptors called adrenergic receptors, which are present in the target organs. Adrenergic receptors are of 2 types: α adrenergic receotor β adrenergic receptor Circulating E & NE have similar effects of sympathetic stimulation. effect of adrenal hormones is prolonged 10 times more than that of sympathetic stimulation.

10. It is because of slow inactivation, slow degradation & slow removal of these hormones. Effect of E & NE on various target organ depend upon the type of receptors present in the cells of target organ. E acts through both α & β receptors equally. NE acts mainly through α receptors & occassionaly through β receptors.

11. FACTORS THAT CONTROL SECRETION Position of individual (standing increases NE secretion) Exercise Cigarette smoking Hypoglycemia Ketoacidosis Anesthesia Surgery (both E & NE secretion) The release of NE is controlled by the actvation of α 2 receptors of the presynaptic memberane , this stimulation inhibits the release of NE. This mechanism is used by certain drugs to treat hypertension.

12. METABOLISM OF CATECHOLAMINES 85% of NE is taken by the sympathetic adrenergic neurons. Remaining 15% of NE & E is degraded .

13. Methylation of adrenaline & nor adrenaline is to meta nephrines (meta adrenaline & meta nor adrenaline) is by catechol -o-methyl transferase (COMT). Oxiadation of metanephrines into vanillyl mandelic acid (VMA) is by mono amine oxidase (MAO).

14. FUNCTIONS E increases BMR, so called cholinergic hormone . E increases oxygen consumption & carbondioxide removal. E increases glucose level in blood by increasing glycogenolysis in liver & muscle. E decreases coagulation time. E has stronger effect on heart than NE, it increases overall activity of heart. NE has strong effects on blood vessels, causes constriction of blood vessels. So it is called general vasoconstrictor. E increases the rate & force of respiration

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