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Cortisol

Cortisol (hydrocortisone, C21H30O5 ), is a corticosteroid hormone synthesized in the zona fasciculata of the cortex of the adrenal glands. Its systematic name is 11,17,21-Trihydroxypregn-4-ene-3,20-dione and its CAS number is 50-23-7. The molcular weight is approximately 362.47.

The amount of cortisol present in the serum undergoes diurnal variation, with the highest levels present in the early morning, and lower levels in the evening, several hours after the onset of sleep. Information about the light/dark cycle is transmitted from the retina to the paired suprachiasmatic nuclei in the hypothalamus. Changed patterns of the serum cortisol levels have been observed in connection with abnormal ACTH levels, clinical depression, psychological stress, and such physiological stressors as hypoglycemia, illness, fever, trauma, surgery, fear, pain, physical exertion or extremes of temperature. There is also significant individual variation, although a given person tends to have consistent rhythms.

Some effects of cortisol being secreted into the bloodstream are an increase in blood pressure and glucose concentrations. Also it increases the glycogen formation in the liver (Freeman, 2002). The release of cortisol inhibits functioning of the immune system, and bone formation.

Cortisol also inhibits the secretion of corticotropin releasing hormone (CRH), resulting in feedback inhibition of ACTH secretion. Some researchers believe that this normal feedback system may break down when animals are exposed to chronic stress.

Most serum cortisol, all but about 4 percent, is bound to proteins including corticosteroid binding globulin, CBG, and albumin. Only free cortisol is available to most receptors.

As an oral or injectable drug, cortisol is used medically in the treatment of anaphylaxis and other severe allergic reactions, and to reduce certain forms of swelling or edema. In normal release, cortisol has widespread actions which help restore homeostasis after stress. It acts as a physiological antagonist to insulin by promoting breakdown of carbohydrates, lipids, and proteins and so mobilising energy reserves. In addition, immune and inflammatory cells have their responses to stress attenuated by cortisol.

These normal endogenous functions are the basis for the physiological consequences of chronic stress - prolonged cortisol secretion causes muscle wastage, hyperglycaemia, and immune / inflammatory responses. The same sequelae arise from long-term use of glucocorticoid drugs.

Synthesis

Cortisol is synthesized from progesterone, the precursor of all steroid hormones. The conversion involves hydroxylation of C-11, C-17 and C-21.

Image:Reaction-Progesterone-Cortisol.png

References

  • Freeman, Scott (2002). Biological Science. Upper Saddle River, Prentice Hall Inc.

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