FIGURE F20.2.1 • Photomicrograph of a glomerulus in Goodpasture syndrome. a. In this Mallory trichome-stained specimen obtained from a kidney biopsy, the collagen molecules in the mesangial matrix and glomerular capillaries are stained dark blue. The bright red stain within the renal corpuscle represents fibrin, which leaked out of the glomerular capillary loops into the urinary space. A cellular crescent (outlined in dashed line) is formed by deposition of fibrin infiltrated by macrophages and proliferated parietal cells of the Bowman capsule. The light blue color surrounding the glomerulus is reflective of edematous reaction containing cells mediating inflammatory reactions. Note the basal lamina of a parietal layer of the Bowman capsule. 320. b. This immunofluorescence image of the renal corpuscle shows the glomerular basement membrane labeled with antibodies directed against human IgG and visualized with secondary antibodies conjugated with fluorescent dye. In Goodpasture syndrome, IgGs bind to the NC1 domain of type IV collagen (3 chain) found in the GMB. Note the irregular thickness pattern of the GBM surrounding capillary loops. The remaining space is occupied by the cellular crescent. 360. (Courtesy of Dr. Joseph P. Grande.) endothelial cell foot processes of podocytes glomerular basement membrane endothelial cell fenestrae of endothelial cell mesangial cell mesangial matrix foot processes of podocytes
FIGURE 20.16 • Schematic diagram showing the relationship between the intraglomerular mesangial cells and the glomerular capillaries. The mesangial cell and its surrounding matrix are enclosed by the basal lamina of the glomerular capillaries. Note that the mesangial cells are in the same compartment as the endothelium and that they can be intimately associated with the basal lamina as well as with the endothelial cells. (Modified from Sakai T, Kriz W. The structural relationship between mesangial cells and basement membrane of the renal glomerulus. Anat Embryol 1987; 176:373–386.) vascular pole of the renal corpuscle is the terminal portion of the distal straight tubule of the nephron. At this site, the wall of the tubule contains cells that are referred to collectively as the macula densa. When viewed in the light microscope, the cells of the macula densa are distinctive, in that they are narrower and usually taller than other distal tubule cells (see Fig. 20.7). The nuclei of these cells appear crowded, even to the extent that they appear partially superimposed over one another, thus the name “macula densa.”
In this same region, the smooth muscle cells of the adjacent afferent arteriole (and, sometimes, the efferent arteriole) are modified. They contain secretory granules, and their nuclei are spherical, as opposed to the typical elongate smooth muscle cell nucleus. These juxtaglomerular cells (see Fig. 20.7) require spe cial stains to reveal the secretory vesicles in the light microscope.
The juxtaglomerular apparatus regulates blood pressure by activating the renin–angiotensin–aldosterone system.