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THYROID GLAND The thyroid gland, shaped like a butterfly, lies in the anterior part of the neck, below the larynx (fig. 1-47). It consists of two lobes, one on each side of the upper trachea, connected by a strip of tissue called the isthmus. The thyroid secretes the iodine containing hormone thyroxin, which controls the rate of cell metabolism. Excessive secretion of thyroxin raises the metabolic rate and causes hyperthyroidism. This condition is characterized by a fast pulse rate, dizziness, increased basal metabolism, profuse sweating, tremors, nervousness, and a tremendous appetite coupled with a loss of weight.
Figure 1-47.-Major endocrine glands. Iodine is essential for the formation of thyroxin. Simple goiter, a diffuse and painless enlargement of the thyroid gland, was once common in areas of the United States where the iodine content of the soil and water was inadequate. In simple goiter, the gland enlarges to compensate for the lack of iodine. To prevent formation of a simple goiter, iodine- containing foods, such as vegetables, iodized salt, and seafood, should be eaten. A condition known as hypothyroidism is caused by an insufficient secretion of thyroxin. The patient exhibits a decrease in basal metabolism, and sweating is almost absent. There may be a weight gain and constant fatigue. The heart rate may be slow, and a simple goiter may form. There may also be personality changes characterized by slow, lethargic mental functioning. Hypothyroidism during childhood can lead to the development of cretinism. Cretinism is a condition characterized by retarded mental and physical development. |
 
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