The Hepatic Sinusoidal Endothelial Cell 



151 



carbohydrate food spontaneously while the protein 

 and the fat was given by stomach tube. After differ- 

 ent lengths of time, usually 1 or 2 hours, the ani- 

 mals are decapitated and specimens from the proxi- 

 mal jejunum are taken for fixation in the usual way. 

 The results obtained are based on studies of speci- 

 mens from 9 animals, 3 for each kind of foodstufT. 



That absorption actually takes place can be ob- 

 served on survey pictures of fat absorption where the 

 cells are crowded with fat droplets. 



In studying the plasma membrane the earlier 

 known distinct, double-contoured structure can no 

 longer be observed. In most places the membrane 

 now appears as a single opaque layer with dilTuse 

 outlines the thickness of which seems to vary with 

 the substance being absorbed. Thus, at carbohydrate 

 absorption the membrane appears thinner than at 

 fat absorption, while the comparatively thickest 



structure is obtained at protein absorption (fig. 2), 

 the total thickness in the last case being about 100 A, 

 i.e. the same as in starving animals. No more exact 

 measurements are performed because of the diffuse 

 outlines of the membrane. 



The results obtained show that absorption from 

 the intestinal lumen occurs through a cell membrane 

 which appears to be able to change its structural 

 organization under different functional states. 



References 



1 . Dalton, a. J., Kahler, H., Strifbich, M. J., and Lloyd, 



B., J. Null. Cancer Inst. 11, 439 (1950). 



2. Grangi K, B. and Baker, R. F., Anat. Record 103, 459 



(1949). 



3. — ibid. 107, 423 (1950). 



4. Zetterqvist, H., The Ultrastructural Organization of the 



Columnar Absorbing Cells of the Mouse Jejunum. 

 Thesis. Karolinska Institulct. Stockiiolm, 1956. 



The Hepatic Sinusoidal Endothelial Cell and Its 

 Histological Relationships' 



H. F. Parks 



Department of Anatomy, University of Rochester School of Medicine and Dentistry. Rochester, !\'ew Yorlc, 

 and the Lalwratory for Biological Ultrastructiire Research of the Department of Anatomy, 



Karolinsl\a Institntet, Stoclxholm 



t/VER since Hoffman and v. Recklinghausen (4) 

 observed the phagocytic character of the endothe- 

 lium of the hepatic sinusoid and v. Kupffer (6) 

 identified his "Sternzellen" as potent phagocytes, 

 this endothelium has been a subject of considerable 

 attention. Failure of silver precipitation methods to 

 demonstrate cell outlines has suggested that the 

 endothelium is either syncytial or discontinuous (2). 

 Finally, the existence of a perisinusoidal space is 

 still being claimed ( I) and denied (3) in contemporary 

 writings. These several points of interest emphasize 

 the need for continued electron-microscopic study 

 of sinusoidal endothelium and its histological rela- 

 tions. 



This report deals with the external shape of sinu- 

 soidal endothelial cells, their relation to one another 

 and to hepatic cells, and to the physiological implica- 

 tions of these relationships. 



The observations herein recorded were made as a 

 companion study to an investigation of phagocytosis 

 also reported in this volume (5). Details of tissue prepara- 

 tion may be found in that paper. 



The endothelial lining of the sinusoid appeared in 

 places as a single sheet of cytoplasm of variable 

 thickness (fig. 1), the thinnest places being less than 

 200 A thick. In other places it was bilaminar, pre- 



^ Partially supported by a grant from the National Science 

 Foundation, Washington, D.C., U.S.A. 



sumably because of extensive overlapping of the 

 cytoplasm of two neighbouring cells (hg. 2). A few 

 sections were seen in which it was tri-laminar and 

 appeared to consist of numerous overlapping sheet- 

 like processes of cytoplasm (described below). 



Shape of cells. — Hepatic sinusoidal endothelial 

 cells of the mouse are very complicated in shape. 

 It will be easily appreciated that no exact description 

 of cell shape can be given because of the limitations 

 of interpretation imposed by the thinness of sections 

 suitable for electron microscopic study; however, cer- 

 tain morphological characteristics have been noted. 



Sinusoidal endothelial cells, at least many of them, 

 are not typical squamous cells like those lining ordi- 

 nary blood capillaries. Irregularity of shape and long 

 cytoplasmic processes are discernible with the light 

 microscope in ordinary histological sections. Finer 

 cytoplasmic extensions have also been seen in this 

 study; sheet-like and trabecular processes. 



The expression "sheet-like" is intended to describe 

 narrower extensions (I to 3 /< wide and .^^ to I n 

 thick) of the usual thin sheet of cytoplasm surround- 

 ing the nucleus of an endothelial cell, (it is of course 

 possible that they are really tangential sections of 

 the periphery of more or less rounded cells.) Such 

 structures were seen apparently hanging free in the 

 lumen, or beneath the main stratum of endothelial 

 cell cytoplasm lining the sinusoid, or actually con- 

 stituting the endothelial lining in places. 



