314 ANIMAL BIOCHEMISTRY 



of glucose is used to overcome the excess. Insulin shock therapy has 

 been reported beneficial in the treatment of schizophrenia, but the 

 results are still in doubt. 



Insulin functions in stimulating the normal oxidation of sugar and 

 the normal deposition of glycogen in liver and muscle. It is not essen- 

 tial in the known schemes of glycolysis since glycogen deposition can 

 occur in the muscles of pancreatectomized dogs. Also, the synthesis of 

 glycogen in vitro by isolated enzyme systems does not require, or re- 

 spond to, insulin. An earlier, attractive suggestion that insulin is di- 

 rectly involved in the glucokinase system is not supported by experi- 

 mental evidence, although an indirect role through counteraction of 

 the inhibitory influence of the adrenohypophysis and the adrenal 

 cortex has not been eliminated. The suggestion has also been made 

 that insulin is necessary for oxidative phosphorylation. Here again, 

 direct involvement has not been demonstrated in in vitro systems. 

 Insulin has been implicated in glucose transport across cell membranes. 

 Glycogen formation by rat hemidiaphragms is stimulated by insulin 

 addition. At the same time, lactic acid production is not affected. This 

 observation has led to the suggestion that the glycolytic pathway stimu- 

 lated by insulin is a route separate and distinct from the classical 

 Embden-Meyerhof pathway. 



Until more knowledge is available it will be impossible to define 

 the function of insulin in metabolism. The role of this hormone may 

 well be multiple in nature. 



Adrenal glands. The adrenal glands, sometimes called the suprare- 

 nal glands, are small bodies, one situated on the upper end of each 

 kidney. In human beings each gland weighs about 3 g. The adrenal 

 consists of an inner portion, the medulla, an offshoot of the sym- 

 pathetic nervous system, and an outer portion, the cortex. Each 

 anatomical portion has its own endocrine characteristics. 



ADRENAL MEDULLA. Two hormones are secreted by the medulla: 

 adrenaline, or epinephrine, and noradrenaline, or norepinephrine. 

 The chemical structures of these two hormones are closely related to 

 that of the amino acid, tyrosine. 



CH.— CH— COO- 



1 ■ 1 



o 



H 



tyrosine 



