Sean, a 42-year-old single father, goes to his physician complaining of nausea and chronic fatigue. He reports having felt fatigued and listless for about half a year, but he had attributed this to stress. He has lost considerable weight and, strangely, his skin has a healthy tan, even though he spends long hours at work and rarely ventures outside. His doctor finds very low blood pressure and a rapid, weak pulse.

Blood tests show that Sean does not have anemia, but his plasma glucose, cortisol, and Na+ are low, and his plasma K+ is high. His doctor orders an ACTH stimulation test, in which Seans secretion of cortisol is measured after he is given a synthetic form of ACTH.

(a) What would account for Seans low plasma Na+ and high plasma K+?

(b) What is the reason for doing an ACTH stimulation test?

(c) What gland is primarily affected if ACTH does not cause a normal elevation of cortisol secretion? What is this abnormality called?

(d) What gland is primarily affected if ACTH does cause an elevation of cortisol secretion?