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Where is the thyroid gland and what does it do?

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Question: Where is the thyroid gland and what does it do?
Diseases of the thyroid gland are common in dogs and cats (humans, too). Dogs with thyroid disease are more commonly hypothyroid (underactive gland) and cats with thyroid disease are more commonly hyperthyroid (overactive gland). This article discusses thyroid anatomy, common conditions and treatment options for dogs and cats with thyroid disease.
Answer: What is the thyroid gland, and what does it do?
The word "thyroid" is of Greek orgin, and means "shield-shaped".1 The thyroid glands are a pair of butterfly-shaped glands at the base of the neck, where the trachea (windpipe) enters the chest. The thyroid secretes and regulates hormones responsible for metabolism and organ function. The thyroid gland is regulated by brain (hypothalamus and pituitary).

What are common problems with the thyroid gland?
The two most common problems with the thyroid gland are hypothyroidism (underactive gland) and hyperthyroidism (overactive gland). Inflammation, other disease proceseses, tumors, anatomical problems, nutrient imbalances, and medications are a few of the many causes of thyroid problems.

What are common signs seen with HYPOthyroidism?
People and animals with a low functioning thyroid gland usually have a reduced level of metabolism. Common signs include:

  • weight gain
  • poor hair coat and hair loss
  • depression
  • poor body condition and reduced muscle tone
  • prone to illness
  • lethargy, seeks warmth to maintain body heat
  • slow heart rate

Hypothyroidism is more commonly seen in dogs, with some breeds (i.e. Golden Retrievers) more prone to being hypothyroidism than other breeds.

What is the treatment for hypothyroidism in dogs?
Treatment is to give replacement thyroid hormones daily in the form of a pill.

What are common signs seen with HYPERthyroidism?
People and animals with a overly active thyroid gland usually have a increased level of metabolism. Common signs include:

  • weight loss
  • increased appetite
  • increased activity
  • vomiting and diarrhea
  • increased thirst and urination
  • always "hot" -- seeking cooler temperatures
  • fast heart rate

Hyperthyroidism is more commonly seen in cats, especially senior cats. Some cats do not show the signs mentioned above, and they are termed "Apathetic Hyperthyroid" cases.

What is the treatment for hyperthyroidism in cats?
There are three treatment options for hyperthyroidism in cats: medical (pills), surgery (removal of the thyroid gland) and radioactive iodine treatment (medicine to selectively kill the diseased thyroid cells). These treatment options will be discussed in detail in the upcoming article in this series.

Related Reading:
Apathetic Hyperthyroidism - Personal story of my cat, Herman
From the About.com Veterinary Medicine Guide, Janet Tobiassen DVM
Feline Hyperthyroidism
From the About.com Cats Guide, Franny Syufy
Feline Hyperthyroidism FAQ
From the About.com Thyroid Guide, Mary Shomom

References:
Thyroid1 Chicago Manual Style (CMS): thyroid. Dictionary.com. Dictionary.com Unabridged (v 1.1). Random House, Inc. http://dictionary.reference.com/browse/thyroid (accessed: October 01, 2007).

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