[Campbell Biology P.1067] Patient X exhibits symptoms of Cushing's syndrome. After administra... | Practice Question

Patient X exhibits symptoms of Cushing's syndrome. After administration of dexamethasone, a drug that blocks ACTH release, their cortisol levels remain high as shown in the graph. Which gland is most likely affected in Patient X?

  • A: Hypothalamus
  • B: Pituitary gland
  • C: Adrenal gland
  • D: Thyroid gland

Explanation

Cushing's syndrome can be caused by excessive activity of either the pituitary or the adrenal gland. Dexamethasone is a synthetic glucocorticoid that normally blocks ACTH release from the pituitary. If the pituitary were the problem, dexamethasone would suppress ACTH, leading to lower cortisol. However, if the adrenal gland itself is hyperactive and producing cortisol independently of ACTH stimulation or even despite suppressed ACTH , then cortisol levels would remain high. The graph shows that in Patient X, dexamethasone administration green bar did not lower cortisol levels compared to when no drug was given orange bar , indicating the adrenal gland is autonomously overproducing cortisol.