Endothelial cells in the rectal venous plexus. An electron microscopic study

The endothelial cells of the rectal venous plexus were studied by electron microscope. The endothelial cytoplasm contained numerous specific granules, intracytoplasmic filaments, and 'anchoring filaments'. The present observations suggest that specific endothelial granules are formed in the Golgi apparatus. Thin 50-70 A and thick filaments 100-120 A were found in the endothelial cytoplasm. Also anchoring filaments between the plasma membrane of the endothelial cells and the underlying basement membrane (or subendothelial microfibrils) were present. The cytoplasmic filaments as well as the anchoring filaments are thought to be a support for the endothelial cells, functioning as a cytoskeleton.