This mechanism is finely tuned, and as the levels of T3 and T4 rise in the bloodstream the production of TSH from the pituitary gland is reduced. Conversely, as the levels of T3 and T4 fall, the pituitary gland secretes more TSH to increase the activity of the thyroid gland. It is essential that the blood levels of the hormones T3 and T4 produced by the thyroid are maintained within narrow limits. Disorders of the thyroid gland Disorders of the thyroid gland are often unnoticed in the early stages, because the symptoms can be slow to develop. Close family and friends may not be aware of the changes but someone who has not seen the patient for a year or longer is more likely to notice.
Disorders normally result from underactivity or overactivity of the thyroid gland.
Underactivity of the thyroid gland Hypothyroidism or myxodoema affects about one per cent of the adult population. It is more common in women than men, usually affecting them between the ages of 30 and 60 years. Occasionally they may lose weight because of faulty metabolism. Their faces often become full and puffy, particularly in the areas around the eyelids and the outer third of their eyebrows may lack hairs. Head and body hair becomes scanty and thin, lacking its natural lustre, and nails may be slow growing and develop ridges.