THE ABSORPTION OF PARTICLES BY THE LYMPHATICS OF THE DIAPHRAGM

¹ Sir William Dunn School of Pathology, Oxford

The absorption of particles from the peritoneal cavity by the terminal lymphatics, or lacunes, of the rabbit's diaphragm has been studied with the light and electron microscopes. Absorption occurs predominantly through those parts of the peritoneal surface of the diaphragm which overlie the lymphatic lacunes. These parts are referred to as the lacunar roofs.

The mesothelial cells of the roofs have features which distinguish them from mesothelial cells elsewhere on the peritoneal surface of the diaphragm. The cells are more closely set, stain more darkly, and separate from each other more readily, particularly at the base of the intercellular junctions. They are supported by a lattice of coarse and fine fibres. In the meshes of this lattice mesothelial and lymphatic endothelial cells are separated only by the basement membrane of the mesothelium which in places may be incomplete.

Erythrocytes pass through the roof into the lumen of the lacune through gaps which are formed by separation of the mesothelial cells and of the endothelial cells at the intercellular junctions. Particles of India ink and colloidal particles of thorium dioxide and saccharated iron oxide enter the intercellular spaces of the mesothelium and spread freely within the meshes of the fibre lattice. These particles appear to pass through the mesothelium by a predominantly extracellular pathway and probably enter the lymphatic lumen through temporary channels which are formed by separation of endothelial cells at the intercellular junctions.

Absorbed colloidal particles accumulate in the cytoplasm of mesothelial and lymphatic endothelial cells in the roofs and a proportion of absorbed material may be transported intracellularly through these two layers in cytoplasmic vesicles. Lymphatic endothelial cells at other sites in the diaphragm can take up colloidal particles from the lumen of the lymphatics.

Note:

We are indebted to Dr. G. A. Meek for the electronmicrograph illustrated in fig. 48 and for his advice on the preparation of specimens for electron microscopy. We thank Mrs. J. Tucker, Miss M. Hoffmann and Messrs. D. W. Jerrome and J. H. D. Kent for their technical assistance, Mr. F. Bradley for his help with the photography, and Miss C. Court for the drawings of figs. 1 and 2.

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