The Most Important Cortisol Binding Globulin-Transcortin

Secretion of Adrenal Hormones

Free Online Lectures of Biochemistry for Medical, Dental and Allied Health Sciences by Biochemistry Club

  • Secretion of all adrenocortical hormones is under the control of ACTH.
  • The diurnal variation of secretion of cortisol (highest values early in the morning and minimum at night) parallels the pulsatile release of ACTH from anterior pituitary under the influence of CRF.
  • Cortisol exerts the negative feedback effect on ACTH secretion.
  • The ACTH also increases the secretion of aldosterone.
  • The level of aldosterone is also affected by position, highest values in upright posture and lowest while lying down.
  • All steroid hormones act through intracellular messengers and increase the rate of transcription.

Transport & Metabolism of Cortisol

  • Approximately 70% of cortisol in blood is bound to an alpha-1-globulin called Cortisol Binding Globulin (CBG) or Transcortin.
  • About 20% is bound to albumin and the rest is free, which is the biologically active fraction.
  • The half-life of cortisol is about 2 hours.
  • The steroid hormones are metabolized and inactivated by the liver.
  • The major processes are reduction & conjugation.
  • The C21 steroids are reduced to their tetrahydro derivatives, which are excreted as their glucuronides or sulfates in urine.
  • Mineralocorticoids (mainly aldosterone) increase sodium reabsorption from renal tubules, leading to sodium retention and resultant water retention.
  • It acts through Renin Angiotensin System.
  • The sodium potassium exchange at the renal tubules leads to increased potassium excretion.
All these lectures are organized and listed in detail in their proper sections. To view these lessons please visit the Hormones & Signal Transduction Section. This can be approached by directly clicking the Biochemistry II button or it can also be approached from the drop down menu in Biochemistry II tab. Once you reach the section click the curriculum tab to view the full list in the section.
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