Which of the following statements regarding the physiology of the adrenal gland are true?

e. None of the above

The proximate stimulator of cortisol production is the peptide hormone, andrenocorticotropic hormone (ACTH). It originates from the anterior pituitary gland and is regulated by corticotropin-releasing hormone (CRH). The regulation of CRH is controlled by various neural influences. These include intrinsic central nervous system influences and a negative feedback inhibition by cortisol. Although there is some evidence of a short-loop feedback of ACTH on CRH, both slow and fast feedback by cortisol on the pituitary release mechanism are the primary sources of clinically relevant CRH regulation. The steroidogenic pathway involves the conversion of cholesterol to pregnenolone, progesterone, 17-hydroxyprogesterone, and then either to the adrenal androgens or cortisol via several intermediates. The 17-ketosteroids reflect adrenal androgen synthesis while the 17-hydroxysteroids reflect cortisol synthesis.

Renin is produced predominantly in the juxtaglomerular apparatus of the kidney where it acts locally and is released into the systemic circulation. Renin cleaves angiotensin I, a decapeptide derived from the liver which serves as renin substrate. Angiotensin I undergoes enzymatic cleavage in the lung to angiotensin II, which is the biologically active form of the peptide. The plasma half-life of ACTH is short (measured in minutes) with a rapid onset of action. This is in contrast to a longer plasma half-life and a slower onset of action for cortisol itself.