A dog's pituitary gland produces the hormone ACTH, which stimulates the adrenal glands to secrete cortisol. Cortisol helps regulate body weight, mineral balance, the structure of connective tissue, the production of white blood cells, and skin health. When cortisol levels are low, the pituitary gland secretes ACTH. When cortisol levels are high, the pituitary gland stops secreting ACTH. Based on this information, which of the following would most likely be the cause of elevated levels of cortisol in a dog?
A. Undersized adrenal glands
B. An excess of ACTH
C. An inactive pituitary gland
D. An immune response to the excess level of cortisol