CHAPTER LXXXVII 



THE PITUITARY BODY 



Structural Relationships 



Situated at the base of the brain and lying in the sella turcica, the pituitary body 

 in man does not weigh much more than half a gram. It is connected with the brain by 

 a funnel-shaped stalk, the infundibulum. On account of a natural cleft, which runs 

 across the gland in an oblique plane, it is an easy matter to split it into two portions, 

 an anterior, or pars glandularis, and a posterior, or pars nervosa. This cleft in the 

 case of man is usually found to be more or less broken up into isolated cysts containing 

 a colloid-like material, and it represents the remains of the original tubular structure 

 from which the pars glandularis is developed; namely, a pouch growing out from the 

 buccal ectoderm. 



On histologic examination it will be found that the pars glandularis consists of masses 

 of epithelial cells with large sinus-like blood capillaries lying between them. These 

 blood vessels are very numerous, so that in an injected gland this portion of the pituitary 

 stands out very prominently. The vessels are derived from about twenty small arterioles 

 that converge toward the pituitary from the circle of Willis, and enter the gland by the 

 infundibulum or stalk by which the gland is connected with the base of the brain. Three 

 types of cell can be differentiated: nonstaining (chromophobe) and granular (chroma- 

 phil), of which latter there are cells with acid-staining and others with base-staining 

 granules, the former being by far the more numerous (Schafer). In some animals such 

 as the cat, the cells of the pars anterior are arranged around the blood sinuses in rows 

 as in a columnar epithelium. The cells with acid-staining granules are said to become 

 much increased in number in pregnancy and also in the enlarged gland of acromegaly 

 (see page 816). After thyroidectomy it has been observed that colloid-like masses ac- 

 cumulate in the pars glandularis, the cells sometimes arranging themselves around these 

 masses as in the thyroid gland. The colloid, however, contains no iodine. 



The posterior part of the gland, or pars nervosa, is composed almost entirely of 

 neuroglia, cells, and fibers, usually with some hyaline or granular material lying be- 

 tween them, particularly in the neighborhood of the infundibulum, into which it may be 

 traced. It is believed that the active principle of the gland is represented by this ma- 

 terial. The blood supply of the pars nervosa is relatively scanty. 



Between the pars nervosa and the intraglandular cleft above referred to is a layer 

 of cells differing from those of either the anterior or the posterior lobe. This layer of 

 cells constitutes the so-called pars intermedia. The cells are somewhat like those of the 

 pars glandularis, except that they are distinctly granular, the granules being of the neu- 

 trophile variety, that is to say, they stain with neither basic nor acid dyes. Well-defined 

 vesicles, containing an oxyphile colloid material which is believed to furnish the 

 active principle of the posterior lobe, are- of ten found between them. Although well 

 separated by the cleft from the pars glandularis, the pars intermedia is not well separated 

 from the pars nervosa, because many of its cells extend for some distance into the latter 

 between the neuroglial fibers. Certain of the cells in the pars intermedia may be seen 

 in various stages of conversion into globular hyaline bodies, or a granular mass of ma- 



806 



