Both the hypothalamus and the pituitary gland are part of the brain. The hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH).  ACTH travels via the blood to the adrenal gland, where it stimulates the release of cortisol. Cortisol is secreted by the cortex of the adrenal gland from a region called the zona fasciculata in response to ACTH. Elevated levels of cortisol exert negative feedback on the pituitary, which decreases the amount of ACTH released from the pituitary gland.  Strictly, Cushing's<unk>  refers to excess cortisol of any etiology. One of the causes of Cushing's<unk>  is a cortisol secreting adenoma in the cortex of the adrenal gland. The adenoma causes cortisol levels in the blood to be very high, and negative feedback on the pituitary from the high cortisol levels causes ACTH levels to be very low.  Cushing's disease refers only to hypercortisolism secondary to excess production of ACTH from a corticotroph pituitary adenoma. This causes the blood ACTH levels to be elevated along with cortisol from the adrenal gland. The ACTH levels remain high because a tumor causes the pituitary to be unresponsive to negative feedback from high cortisol levels. Cortisol can also exhibit mineralocorticoid activity in high concentrations, worsening hypertension and leading to hypokalemia (common in ectopic ACTH secretion).
Cushing's syndrome pathophysiology
Adrenal insufficiency pathophysiology
Acromegaly pathophysiology
Sheehan's syndrome pathophysiology
Cushing's syndrome other diagnostic studies
Adrenocortical carcinoma risk factors
Cushing's syndrome causes
Adrenal atrophy pathophysiology