The Endocrine System 243 



The Effect of Hypoactivity. — If the ovaries are removed in an 

 immature female, the secondary sexual characters fail to develop. 



THE PITUITARY GLAND 



The pituitary gland has been a familiar structure to anatomists 

 for many hundreds of years. Galen (200 A.D.) theorized that this 

 gland filtered the waste materials from the brain, and this idea was 

 perpetuated in the name given by Vesalius, which means phlegm 

 or mucus. 



This gland is located at the base of the brain in a special bony 

 pocket, the sella turcica, of the sphenoid bone (Fig. 44). It is directly 

 below the hypothalamus, just behind the optic chiasma. In the adult 

 human being it weighs about 0.6 gram in the male and slightly more in 

 the female. 



Both embryologically and histologically the gland is differentiated 

 into two distinct parts. The anterior lobe originates as a dorsal out- 

 pocketing from the embryonic mouth cavity ; the posterior lobe arises as 

 a down pocketing from the ventral floor of the brain. The original 

 connection of the mouth to the anterior lobe disappears, but the 

 connection of the posterior lobe to the brain persists as the slender 

 infundibular stalk. Part of the third ventricle of the brain extends 

 through this stalk into the posterior lobe. 



In most vertebrates a third region can be seen between the two 

 main lobes. This is the narrow intermediate lobe. This intermediate 

 portion is more of a transitional zone than a true lobe although it 

 is quite conspicuous in some animals. 



Although the entire gland is quite richly supplied with blood, the 

 anterior lobe receives the greatest amount and the intermediate lobe 

 the least. 



Histologically, the parts of this gland are quite distinct. The 

 anterior lobe is composed of irregular masses and cords of epithelial 

 cells which are separated by small sinuses and are supported by con- 

 nective tissue elements. Three different types of cells are recognizable 

 depending upon their reactions to different stains. The cells compos- 

 ing the posterior lobe are characterized by branching cells in addition 

 to many nonmyelinated nerve fibers. Within the intermediate lobe 

 the cells are chiefly either granular or nongranular basophilic cells. 

 In human beings, the nongranular cells are occasionally grouped into 

 follicles. This latter lobe is not always clearly defined. 



