318 ANIMAL BIOCHEMISTRY 



thyroid gland that very skillful surgery is required to separate them. In 

 human beings there are at least four types of parathyroid tissues or 

 glands. Two of these, the internal parathyroids, are embedded in the 

 thyroid glands, and two others, the external parathyroids, lie behind 

 the thyroid gland. 



When the parathyroids are removed, experimental animals die 

 within 2 weeks with many typical symptoms, the most distinctive of 

 which is an increase in blood phosphorus and a lowering of blood 

 calcium, accompanied by characteristic muscle contractions (tetany). 



The administration of parathyroid hormone (parathormone) re- 

 lieves tetany, increases blood calcium, decreases blood phosphorus, and 

 increases the phosphatase activity of blood serum. Occasionally a 

 tumor develops on the parathyroid glands, causing hyperparathyroid 

 activity. This is known as von Recklinghausen's disease. In this dis- 

 ease, bones become decalcified and blood calcium values are ab- 

 normally high. 



The parathyroid hormone is protein in nature and has a rather 

 large molecular weight of 500,000 to 1,000,000, although an active 

 fraction with a weight of 20,000 g./mole has been isolated. 



The biochemical mechanism involved in calcium-phosphorus control 

 has not been elucidated. 



Pituitary gland. This small gland, also called the hypophysis, is 

 situated at the base of the brain. Anatomically it consists of three 

 structures, the anterior lobe, the intermediate lobe or pars intermedia, 

 and the posterior lobe. The anterior lobe is the largest and most im- 

 portant portion of the gland, although the posterior lobe is also sig- 

 nificant from the standpoint of endocrine activity. Not much is known 

 regarding the hormone-producing characteristics of the pars inter- 

 media. One hormone, intermedin, has been isolated which, when 

 injected into a minnow, causes a red color at the point of attachment 

 of the thoracic, abdominal, and anal fins. No function has been sug- 

 gested for this hormone in higher animals. 



So many imjwrtant physiological functions have been attributed to 

 the pituitary gland that it is difficult to formulate a satisfactory sum- 

 mary of its more important functions. If the pituitary is removed, a 

 series of abnormalities becomes evident. Young mammals cease to 

 grow, and physical and mental activities are retarded. If the gland is 

 removed from the mature mammal, other endocrine glands tend to 

 atrophy and diminish in hormone production. This is true for the 

 thyroid, the parathyroids, the adrenals, the testes, and the ovaries. 

 Appetite decreases, followed by loss of weight, and protein, fat, and 

 carbohydrate metabolism becomes abnormal. In other words, this 



