THE ENDOCRINE SYSTEM 211 



Hypothyroidism or functional insufficiency of thyroid activity 

 produces three pathological conditions that have been known for 

 a long time, viz., endemic goiter, cretinism, and myxedema. The 

 thyroid gland is enlarged in endemic goiter, but the enlargement 

 is due to an abnormal increase in number of the thyroid cells 

 (hyperplasia) to compensate for a subnormal secretion of effective 

 thyroid hormone; the diminished amount of effective thyroid 

 hormone being the result of insufficient iodine in the food and 

 water. Endemic goiter can be controlled by adding iodine in the 

 form of iodides to food and water. Cretinism is a long-known 

 pathological condition in human beings, marked by atrophy 

 (degeneration) of the thyroid gland and retardation of growth 

 in all parts of the body, including the nervous system and the 

 reproductive organs. Myxedema results from a marked thyroid 

 deficiency in adults and is characterized by reduced metabolism, 

 and general ill health, mental and physical. Usually the skin is 

 thick and dry and the hair falls out. Both cretinism and 

 myxedema respond favorably to the administration of thyroid 

 gland or thyroxine if continued throughout life. 1 



Hyperthyroidism refers to an increased functional activity of 

 the thyroid gland, which, in exceptional cases only, may result in 

 an enlargement, also called a goiter. In Graves' disease or 

 exophthalmic goiter, metabolism, nervous irritability, rate of 

 heart beat, and blood pressure are increased. The skin is moist 

 and flaccid. Surgical removal of a part of the thyroid gland may 

 correct the condition, though not always since nervous factors 

 seem to be involved in addition to hyperthyroidism. 



In general, the thyroid hormone serves to stimulate metabolic 

 processes by maintaining the rate of oxidation at a certain level. 

 Increased thyroid activity raises the level, and decreased activity 

 lowers it. Removal of the thyroid, therefore, has some effect on 

 every organ in the body. However, the functional activity of 

 the thyroid seems to require for its full accomplishment the 

 presence of the thyrotropic hormone from the anterior pituitary 



lobe. 



The colloid content of the follicles of the thyroid gland varies 

 in amount under different functional states. If anterior pituitary 

 lobe is implanted in a normal animal, the contents of the follicles 



J For a different view regarding the cause of goiter see H. M. Jones, The 

 Cause of Goitre, Chicago, 1937. 



