This photomicrograph shows a small portion of the pars distalis (PD); the remainder reveals the pars intermedia (Pl ) of adenohypophysis. The pars distalis shown here contains numerous capillaries filled with red blood cells, thus producing the pars distalis (PD) and the pars nervosa. It borders a small cleft (Cl ) that constitutes the remains of the lumen of Rathke’s pouch. The pars distalis, the anterior lobe of the gland, is its largest part. It contains a variety of cell types that are not uniformly distributed. This accounts for differences in staining (light and dark staining areas) that are seen throughout the pars distalis.
Each of the components of the adenohypophysis; i.e., the pars distalis, pars tuberalis, and pars intermedia, when examined at higher magnification, exhibit features at the cellular level that aid in their identification. These features are described in the following figures as well as those on Plate 81.
basophilic. Chromophobes (C ) are also very numerous in this field. The cytoplasm stains poorly in contrast to that of the acidophils and basophils. The cells are arranged in cords and clumps, between which are capillaries (Cap), some of which can be recognized, but most are in a collapsed state and difficult to visualize at this magnification.
basophils, though, typically, one cell type outnumbers the other in a given region). Chromophobes (C) are also relatively numerous at this site. In this particular region, the chromophobe nuclei are readily apparent, but the cytoplasm of the cells is difficult to discern.
the bright red appearance. The pars intermedia contains a number of small cysts (Cy). The cells that make up the pars intermedia, which is relatively small in humans, consist of small basophils and chromophobes. The basophils have taken up the blue stain, thus making them prominent. To the extreme right is a less cellular area, the pars nervosa (PN ).
KEY A, acidophils B, basophils C, chromophobes Cap, capillaries Caps, capsule Cl, cleft Cy, cysts PD, pars distalis PI, pars intermedia PN, pars nervosa PT, pars tuberalis
The parenchyma of the pars distalis consists of two general cell types: chromophobes and chromophils. Chromophobes stain poorly; chromophils stain well. Chromophils are further subdivided into acidophils and basophils. Basophils stain with basic dyes or hematoxylin, whereas the cytoplasm of the acidophil stains with acid dyes such as eosin. The cytoplasm of basophils also stains with the periodic acid-Schiff (PAS) reaction because of the glycoprotein in its secretory granules. Acidophils can be further subdivided into two groups on the basis of special cytochemical and ultrastructural features. One group, called somatotropes, produces the growth hormone, somatotropic hormone (STH); the other group of acidophils, called lactotropes, produces the prolactin (PRL). The groups of basophils can also be distinguished with the  electron microscope and with special cytochemical procedures. One group of thyrotropes produces the thyroid-stimulating hormone (TSH); another group of  gonadotropes produces the gonadotropic hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH); and a third group of corticotropes produces adrenocorticotropic hormone (ACTH) and lipotropic hormone (LPH). Chromophobes are also a heterogeneous group of cells. Many are considered to be depleted acidophils or basophils.
Pars distalis, pituitary, human, Mallory ×360; inset ×1200.