Disorders of Cortisol Secretion

To help you further understand how negative feedback regulation must be considered when diagnosing endocrine disorders, I have diagrammed how hormone secretion changes. These figures apply to the disorders shown in the table on the lecture outline.

Cushing's Syndrome

In the diagnosis of Cushing's Syndrome, one must first establish that there is hypercortisolism. Cortisol secretion varies extensively during the day, but there is a roughly circadian pattern in which cortisol secretion is at its lowest around midnight, thus cortisol levels are measured at this time. ("Circadian" means "about a day".) The level of ACTH is used to distinguish between primary hypercortisolism and Cushing's disease due to a pituitary adenoma.

adrenal tumor cushing's disease

Adrenal Insufficiency

Primary adrenal insufficiency is referred to as Addison's disease. Addison's disease usually has an autoimmune cause, but can also result from tuberculosis. Note that the damage in Addison's disease will affect both the zona glomerulosa and the zona fasciculata, so there is hyposecretion of both cortisol and aldosterone. While it is true that decreased negative feedback will cause increased ACTH secretion, in practice physicians will actually use a challenge test to make the diagnosis. The challenge test determines the ability of the adrenal gland to respond to exogenously administered ACTH with increased cortisol secretion.

Secondary adrenal insufficiency is known by the appropriately descriptive term hypopituitary adrenal insufficiency. This disorder can result as a consequence of medical therapy with glucocorticoids, as diagrammed below.

addison's disease
              adrenal insufficiency

For further information regarding disorders of cortisol secretion (and a quiz), refer to the Negative Feedback Regulation page.