The thyroid gland is responsible for cellular metabolism in the body. A decrease in the thyroid hormones causes a lower cellular metabolic rate and this affects the body's ability to function properly.
There are two types of hypothyroidism that can affect dogs. The first is called primary or acquired hypothyroidism, which is the most common form of this disorder. Primary hypothyroidism occurs by either one of two methods: when the thyroid gland is attacked by the body's immune system, or when the thyroid gland atrophies, or wastes away, for unknown reasons. The end result in both cases is the inability of the thyroid gland to secrete important hormones that regulate the body's metabolism.
The second type of hypothyroidism is called secondary hypothyroidism, which involves the destruction or malfunction of the pituitary gland in the brainstem. A poorly functioning pituitary gland is unable to produce the TSH hormone that stimulates the thyroid gland's production of the thyroid hormones. When TSH is not produced, neither will the thyroid hormones.
