The endocrine system consists of the organs that produce hormones. Hormones help to regulate body functions, from hair growth to reproduction and everything in between!
Most of these endocrine organs are regulated themselves by an internal feedback system. When enough of a hormone is produced, the organ receives a signal and production stops for a while. When the level drops, the organ gets the signal to produce again.
The endocrine system includes some organs that also belong in other systems, such as the pancreas and the reproductive organs, as their main functions are not just hormone production. Other glands, such as the thyroid, parathyroid, adrenal, and pituitary, are mainly hormone producers.
The thyroid is a two-lobed gland lying by the trachea in the neck. This gland is responsible for making the thyroid hormones that can be so important to a dog's health. Thyroid hormones help regulate a dog's metabolic rate (how fast calories are burned), influence coat growth, and are important for fertility and physical activity levels.
Dogs often have too little thyroid hormone. Dogs with low thyroid levels may be inactive and overweight, with poor coats. Males may be sterile, and females may have trouble conceiving and carrying a litter to term.
The two small parathyroid glands lie next to the thyroid. While small in size, these glands produce important hormones, such as parathormone, which regulates the metabolism of calcium. Calcium is important for bone growth, nerve function, and muscle function. Too much or too little can have disastrous consequences!
If your dog has surgery on the thyroid or in this area of the neck, your veterinarian will closely monitor your dog for a few days to be sure the parathyroid was not damaged. Calcium metabolism must be carefully regulated for good health.
The adrenal glands are another pair of small but mighty endocrine glands. These glands are located next to the kidneys. They produce three classes of hormones.
The glucocorticoids, such as Cortisol, act on carbohydrates and help with stress and inflammation. The catecholamines, such as epinephrine (adrenaline), prepare dogs for fight or flight by dilating arteries, increasing heart rate, and opening airways. Finally, the mineralocorticoids, such as aldosterone, regulate sodium and potassium levels in the body.
Various other hormones, including some of the reproductive hormones, are also manufactured here as well as in the reproductive organs.
The pituitary is a two-part gland located at the base of the brain. The adrenal glands and thyroid all get their working orders from the front part of the gland, the anterior pituitary. In addition, the anterior pituitary produces growth hormone, which acts directly on cells.
The posterior pituitary isn't nearly so busy. Its primary productions are oxytocin, which stimulates uterine contractions at labor and milk letdown for nursing, along with antidiuretic hormone, which acts via the kidneys to regulate how much water is resorbed.