[Ultramicroscopic studies on the drainage system of the human corpus luteum]

The granulosa lutein cells of the human corpus luteum have a specialized system of drainage with a particularly formed extracellular space, by which the steroids pass into the capillary vessels. The extracellular space consists of two partial systems: First one finds, similar to the bile capillaries of the liver, lacune-like widnings of the intercellular space, where numerous microvilli of the lining cells are to be found and which are lined by desmosomes and invaginations of the cell membrane. Second there exist relatively wide canals limited by a granular membrane forming a network of their own among the lutein cells. Both systems contact without direct communication. We believe that first the steroids pass into the intracellular lacunes by diffusion or active transport from where they reach the membrane-lined canals by help of the network they pass on to the pericapillar space from where they diffuse into the blood vessels.