THE ULTRASTRUCTURE OF THE BLOOD VESSEL WALL IN THE PITUITARY GLAND OF THE DOMESTIC FOWL

SUMMARY Ultrastructural features of adenohypophysis blood capillaries in the domestic fowl were examined. The very flattened endothelial cells exhibit organelles and fenestrations comparable to those found in other fenestrated endothelia. The borders of adjacent cells, overlapping for short distances, are joined by button-like and/or adhesion-plaque junctions. The abluminal course of the endothelial plasmatic membrane is regular, unlike the luminal surface which appears polymorphic on account of microvilli and vacuoles protruding into the capillary lumen. The epithelial cell basal lamina, a loose network of collagen microfibrils and the endothelial basal lamina usually separate secreting cells from endothelium; pericytes, lying in a split in the endothelial lamina, intervene between the above mentioned perivascular components; rarely, the basal laminae alone are found.