The endocrine system consists of many different glands located throughout the body and the chemicals that they produce are called hormones. Once the endocrine glands produce hormones, they enter the bloodstream and are distributed throughout the body. Each hormone has a specific function in the canine body, but simply put, hormones help to regulate the body. Hormones may have an effect on only a single organ or may affect almost every living cell in the dog's body.
The Master Gland
Some hormones control the release of other hormones. For example, the pituitary gland, which is located at the base of the brain, produces many hormones. These hormones act on other endocrine glands such as the adrenal glands and cause them to release their own hormones. The pituitary gland is called "the master gland" as it produces the greatest number of different hormones than any other gland. Pituitary hormones control the hormone release from other endocrine glands, including the thyroid, parathyroid, adrenal glands, ovaries, testicles, and pancreas. The release of hormones from the other endocrine glands is controlled by means of a mechanism called a feedback loop controlled by the endocrine glands, hormone levels, and the target organ.
The Hormones of the Pituitary Gland
The pituitary gland produces many hormones in the dog's body. Some examples of hormones produced by the pituitary gland include growth hormone, which controls growth; prolactin, which stimulates the mammary glands to produce milk; and thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to produce its own hormones. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are two hormones produced by the pituitary gland which control heat cycles and ovulation in female dogs. The pituitary gland also produces adrenocorticotropic hormone (ACTH) which causes the adrenal glands to produce cortisol and other hormones; melanocyte-stimulating hormone (MSH), which affects pigment; and antidiuretic hormone (ADH) which regulates the metabolism of water.
The thyroid gland, once stimulated, produces its own hormone, thyroxine. The ovaries, once stimulated by FSH and LH from the pituitary, principally produce progesterone and estrogens. The testes provide testosterone. The pancreas produces the most well-known hormone of all, insulin, which regulates blood sugar. The adrenal glands, once stimulated by the pituitary hormone, ACTH, produce naturally occurring steroids called corticosteroids, mineralocorticoids, and adrenal sex steroids.
Hormones play a very complex role in regulating the body's functions. Without appropriate levels of hormones, any number of different endocrine diseases could occur. Some endocrine diseases such as diabetes, hypothyroidism, and hyperadrenocorticism are commonly diagnosed in dogs. If you are concerned about your dog's hormone levels, consult with your veterinarian today.
Article by: Race Foster, DVM and Angela Walter, DVM