ELECTRON MICROSCOPIC STUDY OF LYMPHATIC CAPILLARIES IN THE REMOVAL OF CONNECTIVE TISSUE FLUIDS AND PARTICULATE SUBSTANCES

Abstract

The removal of connective tissue fluids by the lymphatic capillaries is of fundamen­tal importance in the normal maintenance of fluid balance for body tissues. In addition to restoring extravascular proteins back to the blood stream, the lymphatic capillaries are important in the response of the organism to infection and in the spread of disease to various parts of the body. The early studies of Hudack and McMaster (16) and Drinker and Field (10) clearly demonstrated that an intradermal injection of vital dyes or colloidal opaque particles readily passed from connective tissue spaces into lym­phatic capillaries. More recent studies (6, 19, 20) indicate that fluids and particulate substances gain entrance into lumina of lymphatics via one of two pathways, i.e. (1) across the intercellular cleft of patent junction and (2) across the lymphatic endothelium within pinocytotic vesicles.

In order to gain additional information on the mechanisms involved in this transfer of fluids and particulate substances into lymphatics, the present study was designed to investigate this problem by studying the fate of particulate substances after their injection into the connective tissue. Since intradermally injected colloidal particles are not engulfed by endothelia of blood capillaries, but are rapidly ingested by those of the lymphatics, the latter are identified by the presence of opaque particles within the endothelium as well as their lumina. This communication is concerned with the fine structure of lymphatic capillaries and the transport of various colloidal particles across the lymphatic endothelium of dermal tissue.