The Vascular Arrangements of the Mammalian Spleen

Abstract

1. The circulation through the splenic pulp is an open one, but the Malphigian follicles have closed capillaries. The rate of flow is sluggish in certain areas, notably about the follicles. 2. The ellipsoids are collections of intensely phagocytic mononuclear cells, occurring at or near the termination of the penicillar arteries of the spleen of certain animals. These cells are embedded in a fine reticular framework which acts as a filter for foreign particles. 3. Ellipsoids do not occur in the rabbit. 4. The size of the ellipsoids depends largely upon the need for such tissue at the time. 5. They are not perfect one‐way valves. 6. In the spleen of the cat and dog phagocytosis of Indian ink particles is carried on largely by cells of these structures. 7. After phagocytosis and migration of the phagocytes, regeneration of the ellipsoids occurs by proliferation of the cells at the termination of the penicillus. 8. Marked hyperplasia of the ellipsoids may result from injection of suitable amounts of foreign particles. I wish to express my thanks to Professor JOHN TAIT for assistance during the prosecution of this investigation and in preparation of the manuscript. The expenses of the research were in part defrayed by a grant from the James Cooper Fund of McGill University for Research in Experimental Medicine.

Periarterial macrophage sheaths (Ellipsoids) in cat spleen—an electron microscope study

“…Schweigger-Seidel (1863), after observing that various substances injected into the splenic artery were trapped in the irregular spaces of the sheath, proposed that the structure was primarily a filtration apparatus. The porosity of the capillary wall and the propensity of injected particles to accumulate first in the PAMS were confirmed by later studies (Tait and Cashin, 1925;Mills, 1926;Robinson, 1926;Solnitzky, 1937). Communication of the capillary lumen with the intercellular spaces of the PAMS and the spaces of the red-pulp reticular meshwork also has been shown by plastic casts of the splenic arterial vasculature examined by scanning electron microscopy (Ohta et al, 1977).…”

“…As Schweigger-Seidel(1863) recognized over 100 years ago, PAMS are fine filters capable of efficiently clearing blood of particulate material. Following injection of such colloidal suspensions as trypan blue or India ink, heavy concentrations of particles are localized to the PAMS (Tait and Cashin, 1925;Mills, 1926;Solnitzky, 1937). In contrast, particles in red pulp are distributed about arterial endings in animals that lack PAMS (Mills, 1926;Weiss, 1962).…”

“…sheath (Mills, 1926), sheath of Schweigger-Seidel (Solnitzky, 1937), housses urterielles, and manicotti pericupillari (Dustin, 1975). All of these terms fail to impart information regarding the composition or function of the structure.…”

“…Indeed, the term "ellipsoid is the least appropriate, since it indicates only one of several possible shapes. There is variation in shape and size among the species and even within an individual (Mills, 1926;Solnitzky, 1937;Snook, 1950;Jacobsen, 1971). We have found that these cellular nodules on arterial capillaries consist of a meshwork of stromal cells, reticular cells, and extracellular material with reticular fibers, whose interstices are filled with macrophages.…”

“…The nature and function of the PAMS were important considerations in many light-microscopic studies of the spleen. The divergent opinions resulting from these investigations are reviewed by Tait and Cashin (1925), Mills (1926), and Solnitzky (1937). Despite many points of controversy among early investigators, most agreed that the vessel within the sheath was porous, since the passage of fluid, cells, and particles through the wall of the capillary was demonstrated repeatedly by injection techniques.…”