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ADRENAL CORTEX

BIOCHEMISTRY

mprasadnaidu
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ADRENAL CORTEX

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  1. Adrenal hormones M.Prasad Naidu MSc Medical Biochemistry, Ph.D.Research Scholar

  2. Functional anatomy • 2 adrenal glands / suprarenal glands • Situated on the upper pole of each kidney • Each gland weighs 4 gms • 2 distinct parts (Cortex & medulla ) • A.medulla is the central portion (20%) • A. cortex is the outer portion (80%) • The 2 portions developmentally,functionlly & structurally diff from each other.

  3. Functional anatomy • A. medulla develops from the neural crest, which gives origin to sympathetic nervous system. • So its secretions resemble that of sympathetic nervous system. • A.cortex develops from mesonephros, which give rise to the renal tissues. • It secretes a group of hormones called Corticosteroids

  4. Histology of A. cortex • 3 distinct layers. • 1.Zona glomerulosa:- outer most layer-secretes mineralocorticoids • 2.Zona fasciculata:- middle layer – secretes mostly GCs and to slight extent sex hormones. • 3.Zona reticularis:- inner most layer – mostly sex hormones & slightly GCs.

  5. Hormones of A.Cortex • Adrenocortical hormones / corticosteroids • Synthesized from cholesterol • Degraded mainly in the liver and conjugated to form glucuronides and to a lesser extent of sulphates. • 25% excreted in bile & feces & 75% in the urine • 1. Mineralocorticoids • 2. Glucocorticoids • 3. Sex hormones

  6. mineralocorticoids • Act on the metabolism of the electrolytes or minerals & distribution of water in tissues. • Especially Na & K hence the name • Eg: Aldosterone (0.15µg of daily output) & • (0.006µg% of plasma level) • 11-Deoxycorticosterone(0.2µg)& (0.006) • Synthesis:- CHOLESTEROL • Transport:- Aldosterone binds with plasma proteins (Gbs) – binding is loose – 50% of Aldosterone is found free.

  7. chemistry • C21 steroids • 90% MC activity is by aldosterone. • Aldosterone is 30 times more active than deoxycorticosterone. • Aldosterone is mainly concerned with water salt balance of the body.

  8. Functions of MCs • Ald is essential for life (life saving hormone • Total loss of Corticosteroids causes death within 3 days to 2 weeks • This is mainly bcos of MCs. • Without MCs, the K+ conc of ECF rises • The conc of Na & Cl ions decreases • The total ECF volume and Blood vol are also greatly reduced. • All these changes lead to cardiac dysfunction, shock like state and finally death. • The entire sequence can be prevented by Ald. • Hence it is called life saving hormone.

  9. Functions of MCs • 2 most important functions of aldosterone • ↑reabsorption of Na & excretion of K in the renal tubules. • ↑ secretion of H+ into the tubules to some extent

  10. Other functions • Effect on Na reabsorption :- • Ald acts on the DCT and the collecting duct and increases the reabsorption of Na+ • Effect on ECF volume & B.P:- The MCs cause persistent increase in ECF fluid vol and the blood vol. This finally leads to ↑bp • Effect on K ions:- ↑ K+ excretion through the renal tubules.

  11. Other functions • Effect on [H+]:-when ald ↑ Na+ reabs in the renal tubules, it causes tubular secretion of H+. To some extent it is in exchange for Na ions. • In normal conditions, ald is essential to maintain acid-balance in the body. • In hypersecretion, it causes alkalosis • In hyposecretion, it causes acidosis

  12. Other functions • Effects on sweat glands & salivary glands: • Ald has almost similar effect on sweat & salivary glands as it has on the renal tubules. • Na is reabsorbed from sweat glands under the influence of aldosterone, thus the loss of Na from the body is prevented. • Effect on Intestine:- loss of ald leads to loss of Na and water through the large intestine leading to diarrhea with loss of salt from the body.

  13. Mode of axn • Ald acts through the m-RNA mechanism • The sequence of events are: • i)As ald is sol in lipid, it diffuses readily into the interior of the tubular epithelial cells via the lipid layer of the cell membrane • ii) in the cytoplasm of the tub.epi.cells, ald combines with the specific receptor protein

  14. Mode of axn • iii) the ald.rec.complex diffuses into the nucleus • iv) the m-RNA diffuses back into the cytoplasm. In the cytoplasm along with ribosomes causes protein syn. • One of such enzymes that helps in the tpt of Na & K through NaK pump is the NaK adenosinetriphosphatase

  15. Regulation of secretion • Stimulating agents:- • 1. ↑ in the K+ conc in the ECF • 2. ↓ in the Na+ conc in the ECF • 3. ↓ in the ECF volume • 4. ACTH

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