Because endocrine cells do not release hormones unidirectionally into a duct, they do not show polarity and are not organized into discrete secretory units, such as tubules or acini. Rather, endocrine cells frequently form plates or cords, interspersed with abundant, large-bore, fenestrated capillaries. Pars distalis of adenohypophysis 400x
Peptide-secreting cells >
Peptides form one major classification of hormones. Peptide-secreting cells possess all the organelles needed to produce proteins for export: RER, Golgi apparatus, and secretory granules. Therefore, these cells stain intensely and appear grainy when seen with the light microscope.
- Golgi apparatus >
The Golgi apparatus is responsible for packaging the secretory protein into vesicles. The Golgi appears as an unstained area of the cytoplasm adjacent to the nucleus in these cells.
- Secretory granules >
The content of the secretory granules will cause them to stain differentially. In this image, some cells contain granules that stain with hematoxylin; in other cells, the granules stain with eosin. Secretory granules may be positioned around the entire circumference of the cell, thus validating the lack of polarity in endocrine cells.
Endocrine glands are highly vascular and possess wide-bore, fenestrated capillaries, which facilitate the uptake of hormone into the blood stream.