PROBLEM 6. Hormones Help Regulate Cell Activities 



sufficient calcium salts in the blood. A 

 lack of calcium salts in the blood due to 

 an undersecretion of the parathyroids is 

 dangerous. It causes a certain kind of 

 convulsion or muscle spasm. 



The sex organs, of which you will 

 read more in a later unit, secrete hor- 

 mones into the blood besides performing 

 the function of reproduction. These 

 hormones are responsible for the devel- 

 opment of the characteristics that dis- 

 tinguish males from females. See Figure 

 244. 



The thymus is often mentioned as a 

 ductless gland. There is no clear-cut 

 evidence, however, that it is a ductless 

 gland. It lies behind the upper part of 

 the breast bone. It is comparatively large 

 in young children and grows smaller 

 with age. Its use in the body is not defi- 

 nitely known. 



Year by year new hormones are added 

 to the list of those you have read about. 

 It may well be that as investigation con- 

 tinues other organs may be found to 

 serve as ductless glands. This is a com- 

 paratively new field and much research 

 must still be done before scientists can 

 understand how the complex activities 

 of the cells in all parts of the body are 

 regulated. You will find a review table 

 on hormones at the end of this problem. 



How a complex animal lives and grows. 

 Let us sum up very briefl\' the most im- 

 portant points in this unit. The body of 

 a complex anirnal such as ours has many 

 parts and billions of cells. All the cells 

 are supplied with soluble food and with 

 oxygen. All produce CO.., H.O, urea, 

 uric acid, and other salts in the process 

 of oxidation. The blood and lymph bring 

 the needed substances to the cells and 



BLOODHOUND 



RUSSIAN WOLFHOUND 

 Fig. 245 Certain differences between dogs may 

 be caused by differences in the activities of 

 ductless glands. Can you state ivhat abnormal 

 gland condition fuigbt have produced each of 

 the three breeds of dogs shown above? Do you 

 k7iow ajiother breed in which you iJiight sus- 

 pect ductless glands to have played a part? 



(.AMERICAN MUSEUM OF NATURAL HISTORY) 



