Endocrine System Diseases
Endocrine system diseases are pathological processes of the endocrine glands and diseases resulting from abnormal level of available hormones. The endocrine glands are located in various places throughout the body. They manufacture hormones, which, when released, travel in the bloodstream to reach another gland or part of the body. These hormones regulate body functions in numerous ways. Basically, most overproduction of a hormone known as hyper-, is caused by a tumor or tumors of one of the endocrine glands. Underproduction of a hormone resulting in a deficiency, or hypo-, is usually of unknown cause, or idiopathic. There is some evidence that hormone deficiencies are caused by an autoimmune disease, in which the body attacks its own endocrine system for unknown reasons. In general, endocrine diseases of the dog are treatable either by removal of the tumor or by medication. Left untreated, most endocrine system diseases will cause death within a period of 1 to 2 years. Diagnosis of endocrine diseases is most often made by means of a combination of clinical signs and blood tests.
Located under a dog's chin, thyroid gland makes two main hormones, T4 and T3. The most common problem associated with the thyroid gland is underproduction that results in hypothyroidism. In contrast, hyperthyroidism is marked by overproduction of these hormones. Although rare, hyperthyroidism is often the result of thyroid cancer and, although it can sometimes be successfully treated with radiation and/or chemotherapy, the dog is already too ill for treatment.
The four parathyroid glands lie in the soft tissue around the thyroid gland and secrete parathyroid hormone, which is important in regulation of blood calcium. A deficiency of this hormone (hypoparathyroidism) causes the blood calcium to drop. The decrease in calcium level causes tetany, a disease marked by muscle twitch and spasmes similar to those seen in epileptic seizures. A tumor of a parathyroid gland will cause hyperparathyroidism, a disease characterized by deposition of the excess blood calcium in the kidneys leading to kidney failure.
The adrenal glands are located at the front of each kidney and are divided into two parts, similar to a plum or peach: the inner part corresponding to the pit and the outer to the flesh of the fruit. Each part makes different hormones. The outer part (adrenal cortex) manufactures cortisol/cortisone and aldosterone. Too much cortisone (hyperadrenocortisism) results in Cushing's disease. A deficiency of cortisone and aldosterone is hyperadrenocortisism (Addison's disease). Both diseases are quite common in the dog. The inner part of the adrenal gland is called the adrenal medulla; it produces adrenaline, or epinephrine. A deficiency of adrenaline won't cause any signs. Too much adrenaline can be produced by a very rare tumor called pheochromocytoma that will cause a dog to develop a rapid heartbeat, nervousness, and fever.
Pancreas consists of two parts: endocrine gland and exocrine gland. The endocrine part of the pancreas makes many hormones, the most important of which is insulin. Not enough insulin will result in diabetes mellitus. An overproduction of insulin can be caused by insulinomas (cancers of the pancreas), which occur in older large breed dogs. Signs of this disorder are similar to those found in hypoglycemia.
Gonads include both testicles in males and ovaries in females. In the male, the testicles make testosterone, which is necessary for fertility. A testicular cancer usually makes female hormones, causing a male dog to act more like a female.
Located at the base of the brain, the pituitary gland is known as the "master gland" because it controls and regulates the functions of many of the other glands through the action of its six major types of hormones. Adrenocorticotrophic hormone (ACTH) is released from the pituitary and regulates the adrenal cortex, which manufactures cortisone. A deficiency of this hormone is very unusual, but if there were one, the signs would be similar to those of Addison's disease. An excess will cause the most common type of Cushing's syndrome. Thyroid stimulating hormone (TSH) stimulates the thyroid gland to make T4 and T3. An excess or deficiency of TSH has not been very well defined, but occasionally a tumor on the pituitary can destroy the TSH-producing cells, resulting in an underactive thyroid gland. A deficiency of the growth hormone (GH) in a young dog will result in a dwarf, which happens very rarely. A tumor of the GH-producing cells has never been recorded; however, a condition is seen in older, unspayed female dogs where too much progesterone and estrogen can stimulate GH cell hyperplasia (production of too many GH cells, forcing GH levels to go up and causing acromegaly). Other hormones secreted by the pituitary gland are follicular stimulating hormone (FSH) and luteinizing hormone (LH), both of which are important to stimulating ovaries and testicles. Excess or lack of these hormones are rare and don't seem to cause any serious problems. The sixth hormone is prolactin, which is very important to milk secretion in lactating females.