Introduction to the Endocrine System
In a healthy dog, the endocrine system is a finely tuned “machine", composed of different “parts" (the organs) that communicate with each other via chemical signals called hormones in order to keep each other in check. One of the main organs of the endocrine system, the pituitary gland, is located in the brain and, among other hormones, secretes adrenocorticotrophic hormone (also known as ACTH). As the name implies, this hormone’s action is directed towards the adrenal glands, located far from the pituitary gland, in the area of the kidneys.
As a result of the presence of ACTH in the blood, the adrenal glands secrete glucocorticoids, or cortisone-like chemicals; specifically, they secrete cortisol. Cortisol is involved in many important processes in a healthy body, like the regulation of fat metabolism, immune responses, blood sugar levels and kidney functions. The fine-tuned endocrine system makes sure that just the right amount of cortisol is in the blood; indeed, high levels of cortisol in the blood are a signal for the pituitary to stop secreting ACTH. No more ACTH, no more cortisol. If cortisol levels are low, the pituitary steps up its secretion of ACTH. Therefore, both the adrenal glands and the pituitary glands are constantly communicating with each other to ensure a “dynamic equilibrium" of cortisol in the blood.