Structure and Function of the Endocrine System in Dogs - Page 2

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Structure and Function of the Endocrine System in Dogs

By: Dr. Bari Spielman

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What Are Common Diseases of the Endocrine System?

Diseases of the endocrine system can arise with either overproduction or underproduction of hormones. There are numerous diseases of the endocrine system in dogs.

  • The hypothalamus produces several hormones that tell the pituitary gland to secrete its hormones. The hypothalamus also produces antidiuretic hormone (ADH).

    Diseases of the hypothalamus usually result in decreased function of the pituitary gland. The end result is less secretion of several pituitary hormones such as growth hormone, ACTH, or thyroid stimulating hormone.

    Diabetes insipidus is a disease where the kidneys are unable to retain water because of a lack of antidiuretic hormone. Animals with diabetes insipidus, also known as water diabetes, are profoundly thirsty and urinate excessive amounts.

  • The endocrine disorders associated with the pituitary gland fall into two types: under production of hormones (hypofunction of the gland), and excessive production of hormones (hyperfunction of the gland).

    Undersecretion of pituitary growth hormone (GH) is not very common in the dog, but can occur in both puppies and adult dogs. Insufficient production of growth hormone in puppies results in dwarfism. When the production of GH is abnormally low in the adult dog, hair loss is the major symptom.

    Overproduction of growth hormone causes a disorder called acromegaly. Acromegaly in the dog usually develops as a side effect to the long-term administration of progesterone drugs, but can also develop from a pituitary tumor. Affected dogs develop blunt and broad faces with excessive skin folds on the face and neck. They may develop enlargement of the abdomen, lethargy, weight gain and neurologic signs.

  • There are a number of common disorders associated with the thyroid gland.

    Hyperthyroidism arises when the thyroid gland becomes overactive and excessive amounts of the hormone thyroxine (T4) are released. Too much thyroxine in the body causes multiple clinical signs, including weight loss, increased appetite, vomiting, diarrhea, high blood pressure and sometimes, excessive activity. Hyperthyroidism is uncommon in the dog and most often arises from a cancerous tumor of the thyroid gland.

    Hypothyroidism is a common disorder of dogs. It may arise with immune destruction of the thyroid gland. Some breeds of dogs are predisposed to this condition. With hypothyroidism the thyroid gland does not produces normal amounts of T4. Hypothyroid dogs often become sluggish and gain weight. They seek out warm places, have thin hair coats, and may develop neurologic and other signs.

  • Parathyroid gland diseases are uncommon in the dog, and may reflect either hypofunction or hyperfunction of the parathyroids.

    Undersecretion of parathyroid hormone is called hypoparathyroidism. This condition may develop in young dogs, and may be due to immune destruction of the glands. Because parathyroid hormone is needed to maintain normal calcium levels in the body, hypoparathyroid dogs exhibit signs associated with low calcium. Signs include seizures, muscle twitching and tremors, trouble walking and weakness.

    Oversecretion of parathyroid hormone, or hyperparathyroidism, also results in abnormal calcium levels in the body. This condition may arise with either benign or cancerous tumors of the gland. Calcium levels in the body become very elevated, and may result in kidney damage with increased urination, vomiting, loss of appetite, lethargy and muscle weakness.

  • There are several endocrine disorders of the pancreas.

    Diabetes mellitus (or sugar diabetes) is an important disease of the endocrine portion of the pancreas. This common disorder of dogs arises with underproduction or inappropriately low secretion (release) of insulin. Insulin is the hormone that controls blood sugar and the usage of blood sugar by various organs in the body. Inadequate production of insulin causes the blood sugar to increase. Signs associated with elevated blood sugar include increased thirst and urination, weight loss despite a normal appetite, muscle weakness and development of cataracts.

    Insulinomas are insulin-secreting tumors of the pancreas. Excessive amounts of insulin cause profound hypoglycemia (low blood sugar), and this often results in weakness, disorientation and seizures.

    Other hormone secreting tumors may also develop in the pancreas, but they are rare in the dog.

  • The adrenal glands produce several hormones, but the most common disorders of this gland result in changes in cortisol levels. Cortisol is the cortisone hormone.

    The most common disease of the adrenal gland involves the overproduction of cortisol, also known as hyperadrenocorticism (hypercortisolism) or Cushing's disease. Cushing's disease is usually seen in middle aged to older dogs and often arises secondary to an overproduction of the hormone ACTH by the pituitary gland. A tumor of the adrenal gland may also result in too much cortisol secretion. Excessive drinking, urinating, increased appetite, panting, hair loss and a pot-bellied appearance are typical signs of too much cortisol production.

    A less common disease of the adrenal gland is hypoadrenocorticism or Addison's disease. Addison's disease is seen more commonly in dogs than cats and is caused by a deficiency of two hormones, cortisone and aldosterone. Aldosterone regulates sodium and potassium levels in the body. Dogs with Addison's disease are often weak, have low heart rates, vomiting, diarrhea, low blood sugar, and may be collapsed.

    A tumor of the adrenal gland, called a pheochromocytoma, is a rare cause of high blood pressure in the dog. This tumor causes the overproduction of epinephrine hormone in the dog. It occurs primarily in older dogs.

  • Other less common endocrine disorders involve changes in the amount of circulating fat (lipid) in the body, the underproduction or overproduction of red blood cells, and various functions of the reproductive system.

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