CLINICAL CASES
447
into cortisol by the action of three cytochrome P450 enzymes,
CYP17,
CYP21A2,
and
CYP11B1.
After synthesis is complete, cortisol is released from
the zona fasciculata in the adrenal cortex via free diffusion into the blood
stream for distribution to its target organs, such as liver and kidney.
The adrenal gland produces cortisol in response to intermediate hormones,
called adrenocorticotropin hormone (ACTH) and corticotropin-releasing
hormone (CRH) via the humoral stress pathway, which extends from the
brain to the adrenals (Figure 50-2). Once the body has received an environ-
mental stress signal, it is detected by neurons in the cerebral cortex and trans-
mitted to the hypothalamus. The hypothalamus then releases CRH via the
classic secretory pathway into the anterior pituitary. CRH stimulates release of
Figure 50-2. Induction of the humoral stress pathway. Once an environmental
stress is detected by the CNS, this signals the hypothalamus to release CRH
into the anterior pituitary. ACTH is then released from the pituitary into the
blood and eventually binds membrane receptors in cells of the adrenal cortex.
Cortisol is synthesized and leaves the cell via free diffusion into the blood and
is eventually distributed to the hypothalamus and pituitary to inhibit release of
CRH and ACTH, respectively, through a negative feedback loop.
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