A Study of the Structure of Splenic Sinuses in Man and in the Albino Rat With the Light Microscope and the Electron Microscope

Abstract

The splenic sinuses are the first collecting vessels of the spleen. They follow a tortuous course, ramifying extensively in the red pulp. They vary in development and prominence from species to species (23) but in human beings and in rats they are well developed and constitute a great part of the volume of the entire organ. They are thin-walled structures consisting only of endothelial cells and a delicate supporting connective tissue, the reticulum. Sinal endothelial cells are reticular cells flattened to endothelial form and, as such, represent a portion of the reticulo-endothelial system. They are relatively undifferentiated cells, differing from common endothellum in being phagocytic and, at least under certain conditions, hematopoietic.It is a matter of dispute whether the normal sinal wall is anatomically closed or open. Moreover, it is uncertain whether the endothelium of the splenic sinuses is anatomically continuous with that of the terminal arterial branches or whether these arterial endings open upon the red pulp. This subject has been reviewed by Mall (15), Klemperer (8), Knisely (9), Snook (23), Bj6rkman (1) and Weiss (27).The characteristics of splenic sinuses have been studied by traditional methods of sectioning and staining (14,15,17,23), by tra~sillumination of living exteriorized spleen (9,10,13, 20), and by intravascular injection of various substances (1,14,15). The present work represents a study of the structure of splenic sinuses with the light microscope and the electron microscope, utilizing tissue obtained from children and albino rats. It has been undertaken as part of a larger program of study of the cells of the connective tissues with emphasis on the functions and potentialities for differentiation of reticular cells. It has also been motivated by the hope that study of splenic sinuses with the electron microscope would contribute to the solution of the problem of an "open" vs. a "closed" sinai circulation.

The Red Pulp of the Rabbit Spleen Studied under the Scanning Electron Microscope

“…From the present view-point of cytology, however, it seems probable that the transverse bridges in the sinus As far as the authors know, this was recognized in none of the previous transmission electron microscope studies (WEISS, 1963;GALINDO and FREEMAN, 1963;THOMAS, 1967 The present study strongly suggests that the openings of the sinus wall of the rabbit are permanent structures, though it is likely that their size and shape may vary in accord with alterations of blood pressure in the sinus (OBERNIEDERMAYER, 1926;KNISELEY, 1936;BJORKMAN, 1947). A possible contractility of the endothelial cells (WEIDENREICH, 1901;FOOT, 1925;v.…”

“…The views on the structural relation of the sinus to the cord of Billroth are also controversial. WEISS (1957) declared the latter to be nothing but collapsed sinuses, though this opinion was revised in his later paper (WEISS, 1963). Some authors recognized no difference between the sinus and cord channels with regard to the nature and arrangement of their lining cells (GALINDO and FREEMAN, 1963;ROBERTS and LATTA, 1964), although this view was opposed by other authors (BURKE and SIMON, 1970;HIRASAWA and TOKUHIRO, 1970).…”

“…A possibility cannot be eliminated that some granular substances on the cell surface may represent trace of blood plasma coagulated by fixation and attached to the surface by drying. The tiny pits found on the cell surface may possibly repretent pinocytic caveolae, which have been recognized by transmission electron microscopy (WEISS, 1963;HIRASAWA and TOKUHIRO, 1970).…”

“…A possible contractility of the endothelial cells (WEIDENREICH, 1901;FOOT, 1925;v. HERRATH, 1935) (WEISS, 1957(WEISS, , 1963STOECKENIUS, 1958 and others).…”

“…Since the studies by WEISS (1957WEISS ( , 1963 some electron microscopists have believed that the sinus wall is formed by longitudinally elongated cells lying against one another's lateral surfaces and that potential gaps between them may allow migration of blood cells through them. WEISS (1957WEISS ( , 1963WEISS ( , 1966, JUNG (1958) and THOMAS (1967) recognized occasional gaps filled neither by a blood cell nor by an endothelial cell, whereas many other authors showed none of such fenestrations. SIMON and PICTET (1964), PICTET and his co-workers (1969) indicated a more constant occurrence of fenestrations through which the sinus lumen is continuous to the cord of Billroth.…”