MORPHOLOGICAL FEATURES OF LYMPHATIC AND MESOTHELIAL COMMUNICATIONS IN THE BROAD LIGAMENT OF THE PIG

Abstract

The broad ligament containing uterine, paraovarian, and oviduct lymphatics was examinedin the pig in various phases of the estrous cycle using light, scanning and transmission electronmicroscopy. The architecture of these regions differed and was independent of the lymphangionsof the precollector and collector lymphatic vessels. Lymphangions were separated frommesothelium by connective tissue and/or muscle layers; however, in the vicinity of the thin walledparaovarian sac, large lymphangions were often compressed between two epithelial layers.Numerous lymphatic lacunae were in direct contact with the peritoneal and paraovarian saccavities. The mesothelial lining of the broad ligament and the external and internal epithelium ofthe pig paraovarian sac displayed two distinct cell types. Only smaller cuboidal cells withprominent microvilli extended above the lymphatic endothelium. The surfaces of these cells werediscontinuous and showed: 1) lymphatic stomata, 2) small pores or fenestrae, 3) a superficialnetwork of epithelial-free communications with underlying connective tissue to the paraovariansac in the postovulatory period independent of the lymphatic vasculature, and 4) endothelial(instead of epithelial) cells with crevice-like discontinuities in large portions of the internal sacsurface during the follicular phase of estrus. Numerous lymphatic stomata had orificescomposed of flattened cuboidal cells while lymphatic endothelial cells were characterized bymacula or zonula adherent connections formed within rims of various sizes (up to 50 µm indiameter). During estrus, there were circular (0.5-2.0 µm) and irregular (to 10 µm)interendothelial openings in stomatal orifices with migrating cells.These morphologic findings suggest that absorption and passage of fluid, particles andcells between cavities and the lymphatic lumen in areas of the paraovarian lymphatic plexus inthe pig is feasible.