Morphologic features of lymph vessels in caprine hemal nodes

The distribution and characteristics of lymph vessels in caprine hemal nodes were studied after glutaraldehyde fixation and epoxy resin embedding. Histologically, the lymph vessels were characterized by thin walls and wide lumens containing inspissated lymph in which a few cells were suspended. The lymph vessels contrasted sharply with adjacent blood sinuses that were filled with elements of circulating blood. A circumferential lymph vessel in the cortex joined radial branches in the medulla that met at the hilum to drain through a large efferent lymph channel. Ultrastructurally, the lymph vessel wall comprised endothelial cells supported by a continuous basal lamina, collagen fibrils, and adventitial reticular cells. The cytoplasm of endothelial cells had fenestrations, plasmalemma-associated vesicles, vacuoles, and focal splits that enclosed large compartments. Many compartments contained erythrocytes and lymphocytes. Modifications of the endothelial cells signified their endowment with features that favored transendothelial transport. The distribution of lymph vessels and the finding of only efferent lymph channels are related to the roles of hemal nodes in blood storage by hemoconcentration and in immune defense mechanisms.