244 The Vertebrate Organ Systems 



THE ANTERIOR LOBE 



Due to the fact that the anterior lobe, through its secretions, affects 

 different processes and other endocrine glands, it has been called the 

 "master gland" of the body. While this is a dramatic term, it is not 

 entirely in accord with the facts. All the glands composing the endo- 

 crine system have reciprocal effects upon one another, and this gland 

 is but one of this important system. 



Actually the anterior lobe does secrete a number of different hor- 

 mones. Three types can be recognized : the grozvth hormone, the 

 trophic hormones, and the lactogenic hormone. 



The Function of the Growth Hormone. — Like so many of the 

 endocrine secretions, the control of growth as exercised by this gland 

 was not apparent until abnormal conditions were studied. The normal 

 growth process is an extremely complex one, involving the orderly 

 progression of many processes. In fact the whole process is rather 

 poorly vmderstood, and the part played by this growth hormone is 

 not at all clear. 



Yet when this hormone is not secreted in proper amounts, the 

 effects are startling to say the least. If the hormone secretes exces- 

 sively (hyperactivity) during the growth period, excessive growth 

 occurs, even resulting in gigantism. Hypoactivity produces equally 

 pronounced effects : such individuals fail to grow properly and are 

 known as dtvarjs. Clearly this malfunctioning is the reason for some of 

 the inhabitants of circus side shows. 



Hyperactivity also may occur after full adult growth is attained. 

 In such a case, the condition known as acromegaly develops. In this 

 condition, portions of the skeleton have overgrowths. Thus the supra- 

 orbital ridge thickens, the lower jaw protrudes, the digits broaden, and 

 the soft tissues of the lips, nose, forehead, and scalp may thicken. 



The Function of the Trophic Hormones.— Those hormones of 

 the anterior pituitary which influence other endocrine glands are known 

 as the trophic hormones. Several of these are quite well known and 

 possibly there are others whose functions still remain to be discovered. 



The gonadotropic factors are those which influence the ovaries or 

 testes. Here it is apparent that there are at least two factors. The 

 first of these, designated as FSH (follicle stimulating hormone), stimu- 

 lates the production of follicles and ova in the female and the sperm 

 of the male. The second hormone, known as LH (the luteinizing 



