Fine Structure of Mouse Renal Glomerulus

Present concepts of glomerular structure stem from the classical paper of Bowman (7) who described in 184:~ the vascular pattern of the kidney and the connection between the glomerulus and the renal tubule. Details of the large literature dealing with the structure of the renal glomerulus up to the year 1930 can be found in the reports of McGregor (27) and von Mbllendorff (32). Outstanding is the description of Zimmermann (54) who, in 1933, presented many details of the fine structure of the mammalian glomerulus as seen with the light microscope. The glomerulus has also been studied recently with the electron microscope (Pease and Baker (41), Dalton (9), Oberling et al. (34), Rinehart et al. (46, 47), Reid (44), Hall et al. (15-18), Fawcett (13), Mueller et al. (33), Pease (39, 40), Rhodin (45), Policard et al. (42)). Especially noteworthy have been the studies of Hall, who first recognized that the endothelial lining of the glomerular capillary is fenestrated or perforated with comparatively large pores several hundred Angstrom units in diameter, and who noted that the urinary filtration surface was covered with elongated cellular processes of cells which he termed "podocytes," but which have been known to histologists since Gerlach (14) as epithelial cells--a term used in the present study, in honor of its long historical usage. Hall (15) noted slits between the long processes of his "podocytes," or epithelial cells, and postulated that urinary filtration took place through the large pores of the endothelial cells and the slits between the processes of the epithelial cells. Between these two cells Hall reports a structure which he called "lamina densa," which appears to be nothing but a dense central layer of the basement membrane of the light microscopists such as McGregor (27), von MSllendorff (30-32), Bargmann (1-3), Borst (6), Zimmermann (53, 54), McManus (28, 29), Bensley and Bensley (4), and Ohmori (35) have also described. Through this structure, Hall postulated, filtration must occur. These important observations on the urinary