Mechanisms of Endocrine Control

Leda is a 38-year-old woman who began to experience weight gain, mood swings, and weakness. When her periods became irregular, she went to her physician. Leda’s physician heard the symptoms Leda was concerned about and then ordered a 24-hour free cortisol urine test and an overnight dexamethasone suppression test and measured her serum ACTH levels. The results indicated that Leda had Cushing disease, a condition caused by the hypersecretion of ACTH by the anterior pituitary and resulting in elevated cortisol levels. To confirm the diagnosis, Leda’s physician ordered a cranial MRI to identify the presence of a pituitary tumor.

  1. The dexamethasone test involves the administration of a      synthetic glucocorticoid ( i.e., cortisol). Knowing what you do about      negative feedback mechanisms, how might this test be used to assess      pituitary function?
  2. Describe how the steroid hormones, like cortisol, are      metabolized in the body. What are the advantages of using a 24-hour urine      test to measure this hormone?
  3. Protein-based and steroid-based hormones trigger      cellular responses in different ways. What are the differences between the      mechanism of action of ACTH and cortisol on target cells?