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| Thyroid gland and its hormones |
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The thyroid gland lies as separate lobes on both sides of the trachea. It is the only gland that can produce and store a lot of excess hormone. It is responsible for releasing the two thyroid hormones T3 and T4. The difference between the two is one iodine atom (3 in T3 and 4 in T4). They are responsible for the consumption of oxygen and generation of heat. This increases the basal metabolic rate, increasing the metabolism of carbohydrates and lipids.
Thyroglobulin produced in the body is a precursor to T3 and T4. It requires iodine to make the conversion. This is why table salt that we use is �iodized.� When the body lacks sufficient iodine, thyroglobulin builds up in the thyroid gland, causing a lump on either side of the neck, which is called goiter. Some people have the misconception that the iodine in salt �wreaks havoc on your thyroid.� It is the opposite. The sodium in salt can cause excess water buildup in the body, which causes pressure on arteries, which can lead to heart disease. |
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| Endocrinology |
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| The hormones are regulated by negative feedback. Thyroid stimulating hormone (TSH) is released by the anterior pituitary gland in response to thyrotrophin-releasing hormone (TRH) from the hypothalamus (above the pituitary). TSH stimulates the release of T3 and T4. As the levels of T3 and T4 increase, they in turn inhibit the release of TSH (negative feedback). T3 and T4 do not act on TRH. |
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| Conditions |
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Hypothyroidism is a deficiency in thyroid hormone levels in the blood caused by an under active thyroid hormone. The inverse is hyperthyroidism. Hypothyroidism is not uncommon in humans, dogs (especially greyhounds like my own), and in older horses. Some symptoms are weight gain (�hypo� like hippo, a way to remember the difference) and hair loss. Young mammals that are deficient generally have decreased development both bodily and mentally. Hyperthyroidism is easily detected with a simple blood test and treated with T4 supplementation. Generally speaking, it is usually a chronic disorder, but not serious if on regular supplementation. The output of the hormone may change slightly, but only occasionally does it begin secreting sufficient amount to stop supplementation.
Hyperthyroidism is more common in cats. This can be treated with a cream that is placed in the ear, which slows the secretion of the hormone. Something to note if you are giving your cat this type of treatment is to ensure that you do not get it on your skin and the previous cream should be cleaned off of the ear before applying more. The excess cream on the ear from previous treatments will inhibit the penetration of the chemical into the patient�s skin. |
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