484 METABOLISM, NUTRITION, AND DIET 



The more important organs which, according to our present views, 

 produce internal secretions are as follows: thyroid, parathyroid; pituitary 

 posterior lobe, pituitary anterior lobe; thymus; suprarenal cortex, supra- 

 renal medulla and chromamne tissues; the islands of Langerhans of the 

 pancreas; duodenal mucosa; liver; kidney; testicular interstitial tissue; 

 ovary interstitial tissue and corpus luteum; placenta, and fetus. 



THE FUNCTION OF THE THYROIDS. 



The Thyroid and Accessory Thyroids. 



The thyroid glands with certain structures called accessory thyroids 

 are situated in the neck to either side of the trachea. The gland consists 

 of two lobes, one on each side of the trachea extending from the thyroid 

 cartilage to the level of the clavicle or lower. Often the lobes are con- 

 nected across the mid line by a middle bar or isthmus. The thyroid is 

 covered by the muscles of the neck It is highly vascular and varies 

 greatly in size especially in different parts of the country. The gland 

 vessels are each lines with a single layer of cubicle cells producing different 

 sized follicles filled with a transparent colloid material containing nucleo 

 albumen and the specific secretion of the gland. 



The accessory thyroids are detached portions of thyroid tissue in the 

 neighborhood of the lateral lobes. They are not different in function from 

 the rest of the gland. 



The Function of the Thyroids. 



The thyroids now are known to secrete a specific chemical hormone 

 which tremendously influences the rate of metabolism of the body as a 

 whole. This secretion is produced by the cells of the follicle and diffuses 

 out into the lymph and blood stream on the one hand or into the colloid 

 material on the other. Ultimately, however, it enters the blood stream 

 and is generally distributed throughout the body. 



It has been a long and difficult task to determine the influence of the 

 thyroid upon metabolic processes. This is due in part to the fact that the 

 early work did not distinguish between the thyroids and parathyroids, and 

 in the later work it has been found extremely difficult to eliminate the 

 parathyroids without injury to the thyroids. 



The present view is that the thyroid hormone increases the rate 

 of metabolism throughout the body. This it does largely by virtue of the 

 fact that the iodine containing compound acts as a deamidizer thus 

 hastening nitrogen elimination and the process dependent upon nitrogen- 

 ous metabolism. This last conception rests chiefly on the work of Kendall, 



