CHAPTER LXXXIV. 



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 de- 

 veloped; namely, a pouch growing out from the buccal ectoderm. 



On microscopic examination it will be found that the pars glandularis 

 consists of masses of epithelial cells with large sinus-like blood capil- 

 laries 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 (chromaphobe) and granular (chromaphil), of which latter 

 there are cells with acid-staining and others with base-staining granules, 

 the former being by far the more numerous (Schafer). 60 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 772). 

 After thyroidectomy it has been observed that colloid-like masses ac- 

 cumulate in the pars glandularis, the cells sometimes arranging them- 

 selves around these masses as in the thyroid gland. The colloid, how- 

 ever, 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 between them, particularly in the neighborhood 



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