The thyroid is a small gland that lies just under the skin below the Adam's apple in the neck. Hypothyroidism occurs when the thyroid gland cannot produce adequate amounts of thyroid hormone. This paper will look at congenital hypothyroidism - the form of hypothyroidism present at birth.
The thyroid gland secretes thyroid hormones which control the speed at which the body's chemical functions proceed. Thyroid hormones control the metabolic rate by stimulating almost every tissue in the body to produce proteins, and by increasing the amount of oxygen that cells use. The thyroid gland needs iodine to function correctly, and this is obtained from the diet. Thyroid hormone production is controlled by a feedback mechanism via the pituitary gland (Berkow, Beers & Fletcher, 1997). First the hypothalamus, located in the brain just above the pituitary gland, secretes thyrotropin-releasing hormone; this causes the pituitary gland to produce thyroid-stimulating hormone; thyroid-stimulating hormone induces the thyroid gland to produce thyroid hormones. When the amount of circulating thyroid hormones reaches a certain level in the bloodstream, the pituitary gland produces less thyroid-stimulating hormone; when the blood level of thyroid hormones drops, the hypothalamus senses this and produces more thyrotropin-releasing hormone, which stimulates the pituitary to produce more thyroid-stimulating hormone. This is known as a negative feedback system.
Thyroid hormones exist in two forms: thyroxine (T4), which is produced in the thyroid gland and has only a slight effect on metabolism; and triiodothyronine (T3), the most active hormone, which is formed in the liver and other organs from thyroxine. For normal thyroid function, a number of factors must function cooperatively: the hypothalamus, the pituitary gland, the thyroid hormone-binding proteins in the blood, and the conversion in the liver and other tissues of T4 to T3.
The...