Endocrine Medical terms: Gland, Hormone 

What is a gland? 

A gland is a group of cells that produces a hormone - for example, estrogen - that leaves the gland and affects other cells. There are several types of glands: endocrine, exocrine, autocrine, and paracrine. 

What does a gland do? 
Glands work like the nervous system—they coordinate activities throughout the body. While the nervous system acts quickly but for a short period, glands and their secretions act slowly and cause changes that last for longer periods. Together, nerves and glands coordinate all major activities, including digestion and reproduction. 

What is an Endocrine Gland?
Endo means within, and endocrine system glands secrete materials that are picked up by blood and carried within the body. Endocrine glands are different from the exocrine glands, which have ducts. Exocrine glands produce substances like milk or sweat, which travel through ducts to the outside of the body. Endocrine glands produce substances like insulin, estrogen, and testosterone. 

What is a hormone?
Hormone means “to excite.” A hormone is a chemical that’s made in one place and carried by the blood to another place where it is active. Glands make hormones. For example, endocrine glands in the pancreas produce insulin. The insulin is picked up by the blood and carried to cells, which are then able to use sugar for energy. 

Hormones are often called chemical messengers.


Examples of Endocrine Glands and their Hormones 
Gland:   Hormone Secreted:

adrenal cortex
adrenal medulla
pancreatic islet cells


antidiuretic hormone 
insulin and glucagon
parathyroid hormone
growth hormone, antidiuretic hormone, oxytocin


  • Glands & hormones influence all bodily functions

  • Death occurs if glands don’t function properly

Pet Health 101
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The endocrine glands provide the body with chemicals called hormones. Once produced, hormones enter the bloodstream and most (other than prostaglandin) produce an effect elsewhere in the body. Not all cells within the body are affected by hormones, and only some cells of a particular organ may respond to a specific hormone.

Some hormones control the release of other hormones. For example, the pituitary gland located at the base of the brain produces many hormones. These hormones act on other glands such as the adrenal glands and cause them to release their own hormones. The pituitary gland is called "the master gland" as it provides more kinds of hormones than any other gland. Pituitary hormones control the hormone release from other endocrine glands, including the thyroid, parathyroid, adrenal, ovaries, testicles, and pancreas.

The pituitary gland produces growth hormone, which controls growth; prolactin, which stimulates the mammary glands to produce milk; and thyroid-stimulating hormone (TSH), which stimulates the thyroid gland. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are two hormones produced by the pituitary gland which control heat cycles and ovulation. The pituitary gland also produces adrenocorticotropic hormone (ACTH) which causes the adrenal gland 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.

As one can see, hormones play a very complex role in regulating the body's functions.

Race Foster, DVM
Marty Smith, DVM
Drs. Foster & Smith, Inc. 
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The endocrine system consists of glands located throughout the body, which secrete hormones directly into the blood. A hormone by definition is a substance that is secreted by a gland but exerts its effect elsewhere in the body. These glands include the pituitary gland in the brain, the thyroid and parathyroid glands in the neck, the Islets of Langerhans on the pancreas, the adrenal glands near the kidneys and the ovaries or testicles depending on the sex of the dog. Each of these glands secretes one or more hormones designed to produce a specific effect in the body. Dysfunction of any of these glands will produce serious systemic problems.


Diabetes is a complex, systemic disease resulting from a failure of cells in the Islets of Langerhans to produce insulin, the hormone that helps sugar move into living cells for the production of energy. Without insulin, glucose (sugar) will build up in the bloodstream and body cells will begin utilizing fats and proteins as their primary energy source. Left untreated, diabetes will be fatal, as complications from abnormal metabolism will take their toll on the internal organ function of the dog.

Clinical signs of diabetes include increased thirst, increased urination, increased appetite and weight loss. Cataracts may develop quickly in some patients. In untreated, advanced cases, an unusual odor from the mouth, weakness, depression and vomiting may also be noted. Most dogs are obese prior to the onset of clinical signs but then loose weight as the disease progresses. Because much sugar is passed in the urine, a lower urinary tract infection may occur. Diagnosis is based on history, physical examination and complete blood and urine testing. ((Cataract))

A common complication is that of Diabetic Ketoacidosis, which occurs in cases of long standing, untreated diabetes or where regulation of the disease is not proceeding well. As fats in the body are being utilized as a primary energy source, certain fats are metabolized into ketones. These ketones further impair metabolism and lead to acidification of the blood making the dog even more ill. Some dogs may decompensate and die in a short period of time if prompt, aggressive treatment is not undertaken.


Virtually all cases of diabetes in dogs are insulin dependent, which means that giving insulin shots is the only way to treat the disease. While oral medications are available for humans, these generally have little value in the dog. For general, uncomplicated diabetes mellitus, insulin injections on a set schedule, feeding a lower calorie, high fiber diet prescribed by your veterinarian, regular controlled exercise and spaying your female dog if that has not been done are all important components to treatment.

Most people are able to learn to give the injections at home and become real "pros" in only a short period of time. Daily collection of urine and adjustment of the insulin dose will be prescribed; a fixed daily dose rarely gives top quality results. The urine will contain sugars in proportion to how much sugar is in the blood. By monitoring urine sugar, the amount of insulin needed for optimal results can thereby be calculated. Periodic blood testing at your doctor's office will also be needed to check actual blood sugar levels and monitor internal organ function.

There are dozens of different types of insulin, which each act a bit differently inside the dog. Also, not every dog responds the same; some may be resistant to the insulin and some may metabolize the insulin at different rates. Adjustments based on the response to the injections or running serial glucose tests to calculate the insulin metabolism may all need to be performed. Adjustments in diet or exercise levels may also come into play. The bottom line is that diabetes can be controlled with many dogs having very good quality of life, but in some, the process of regulation may involve a bit more work.

Treatment of Diabetic Ketoacidosis is slightly more difficult. More severe systemic involvement produces the need for intensive care to restabilize the patient and restore normal metabolism. Most dogs are hospitalized, placed on intravenous fluids, electrolytes and bicarbonate therapy to counteract the acidosis of the blood. Regular insulin, which is more rapid acting, will be given, then later when the patient stabilizes, longer lasting insulin treatment will start. Careful care and monitoring is essential for these patients, but if successful, most dogs can return to normal home insulin therapy.


Low production of thyroid hormone is a common disorder in the dog. Golden Retrievers, Doberman Pinschers, Cocker Spaniels, Dachshunds, Irish Setters and the Miniature Schnauzer are all commonly affected but any breed can have the disorder. Most dogs are middle-aged when the onset of symptoms is noticed. Thyroid hormone is responsible for controlling the metabolic rate of cells in the body. When the hormone is absent, the normal function of most every cell in the body declines.

The loss of function of the thyroid gland may occur due to loss of thyroid tissue for various reasons or due to low production of a stimulating hormone by the pituitary gland in the brain. No matter what the cause, the resultant disease is the same, with symptoms ranging from mild to severe.

Clinical signs of hypothyroidism include mild to extreme weight gain, lethargy, reluctance to exercise, cold intolerance and heat seeking, dull coat, increased shedding, loss of hair symmetrically on the body, weakness, skin infections and poor reproductive performance. It is important to note that not all symptoms will be present and the severity will vary greatly between dogs. ((Hypothyroidism))

Diagnosis is based on the history and clinical signs, blood testing, serum thyroid testing, or more specialized thyroid stimulation tests. Many factors and other diseases can influence the production of thyroid hormone. Some dogs have been found to have ordinarily low serum thyroid levels but have normal thyroid function in the body. All these factors should play a role into the final diagnosis of hypothyroidism.


Daily or twice daily oral thyroid replacement works well for most dogs and is relatively inexpensive. Obese dogs should be placed on a reducing diet to speed weight loss and your veterinarian should have several from which to choose. Proper levels of exercise, control of treats a dog receives and regular follow-up exams and monitoring of blood thyroid levels will help provide a good long-term prognosis for most pets.


The adrenal glands secrete several steroidal hormones that perform various functions in the body. Hypoadrenocorticism occurs if the adrenal glands, for whatever reason, decrease or cease to secrete these hormones. The severity of the disease will vary and can mimic other conditions including renal or gastrointestinal disease.

Clinical signs include weakness and collapse, slow heart rate, loss of appetite, vomiting, diarrhea and shock. Not all symptoms will occur in every case, nor with the same severity as previously mentioned. Diagnosis is based on history, clinical signs, blood counts, serum chemistries, urinalysis, X-rays, EKG testing and special testing to determine how the adrenal glands are functioning.


Dogs with mild clinical signs can often be treated with oral prednisolone and flurocortisone in combination to replace missing endogenous steroids. Long term regular blood monitoring will be needed to gauge the amount and frequency of oral medication, but most patients do very well once stabilized.

Dogs that present with severe weakness or acute collapse are in serious condition and require immediate hospitalization. Intravenous fluids to correct fluid and sodium deficits are necessary and injections of dexamethasone and DOCA as initial steroid replacement are needed to stabilize the patient. Most dogs respond well in 24-48 hours and can be switched to oral or injectable medications for long term use. Dogs that have been on medication but stop may collapse as described and need this intensive care to return too normal.


An increase in glucocorticoid (cortisone) output by the adrenal gland is known as hyperadrenocorticism, a disease commonly seen by veterinarians. The abnormalities associated with this condition are due to long term internal exposure to high levels of cortisone. The disease may occur due to pituitary gland dysfunction, adrenal gland tumors and even in conditions where dogs have been taking steroids for long periods of time. Older dogs most commonly acquire this disease.

Canines with Cushing's disease will show signs of drinking and urinating much more than normal, have a bloated and pendulous abdomen, loose hair over both sides of the back and trunk and have increased pigmentation of the skin. They may pant more, have some respiratory difficulty and become somewhat weak. It is not uncommon for these dogs to also develop hypothyroidism or diabetes mellitus. ((Cushings Disease))

Diagnosis is based on these clinical signs, blood, serum and urine analysis, X-rays and special testing of the adrenal and pituitary gland function to secure the diagnosis and pinpoint the cause of the illness.


Long term treatment and management of this syndrome is difficult and sometimes only partially successful. Complications and secondary illness is not uncommon and these need specific treatment. The use of mitotane, which destroys part of the hyperfunctional gland, is commonly used. Ketoconazole, an anti-fungal medication, has also been used with some success. A new drug, Anaparil, will work well in certain cases. Surgical removal of all or part of affected adrenal glands is possible but the surgery is difficult and risky for most surgeons to perform.

Frequent and repeated blood and serum testing, including the adrenal function test is necessary to fine-tune the therapy for optimal results. In the early stages of treatment, tests may be need every few weeks, but your veterinarian will need to individualize a plan to best fit your dog's problem. Secondary diabetes or hypothyroidism needs to be controlled and will only make stabilization more difficult. Long term survival after diagnosis of 1-2 years is considered good.


The parathyroid glands consist of two very small glands on each lobe of the thyroid gland, hence the name. These glands control calcium balance in the body by secreting parathyroid hormone, which increases blood calcium and calcitonin that decreases blood calcium levels. Blood phosphorus levels are partially controlled this way as well and vitamin D also plays a role in this regulatory mechanism.

Conditions of the parathyroid glands are very rare. Hyperparathyroidism may occur if excess parathyroid hormone is secreted. This is usually secondary to parathyroid tumors and the symptoms of illness are usually related to calcium levels in the blood being consistently elevated. Clinical signs include increased thirst and urination, poor appetite, weight loss, lethargy, weakness, muscle twitching, seizures and constipation. Many animals may be without symptoms with the disease being diagnosed during other testing. Often physical examination will be quite normal.

Diagnosis is based on this history, physical examination, blood and serum testing, X-rays, ultrasound and exploratory surgery. Quite a few other conditions may cause abnormal increases in blood calcium levels including various types of tumors, hypoadrenocorticism, renal failure, the increased intake of vitamin D and certain bone diseases. All these need to be explored and ruled out before making a diagnosis of hyperparathyroidism.

Low blood calcium is most commonly associated with eclampsia, or after some type of internal or surgical destruction of the parathyroid and/or thyroid glands. (Hypoparathyroidism) Signs of low blood calcium can be severe and include nervousness, tremors, twitching, muscle spasms, staggering when walking, panting, weakness, increased thirst and urination, vomiting, diarrhea, weight loss, anorexia and depression. Diagnosis is based on this history, physical examination, blood and serum testing, X-rays, ultrasound and exploratory surgery.


Treatment centers first on identification of the primary cause of the calcium variations in the blood. Primary Parathyroid gland tumors may be surgically treated. Dogs with low blood calcium may need intravenous followed by oral calcium and vitamin D supplementation.


The pituitary gland is a small multi-part gland located at the base of the brain near the optic nerves. The pituitary gland's main function is to measure hormone levels in the blood from other endocrine glands and secrete other hormones as needed to turn the various glands on or off as required. The Islets of Langerhans, however, are not regulated in such a fashion.

Disease, dysfunction or tumors of the pituitary gland can lead to dysfunction of any or all of the other endocrine glands producing disease specific for each individual organ. Other conditions such as abnormalities in growth can also occur due to pituitary dysfunction. These conditions are uncommon, diagnosis is complicated and treatment options are often limited to resolving specific endocrine glandular disease.

James W. Day D.V.M., P.C.
Family Vet
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