TEM of several red cells in cross-section within the capillary loop (any of the small blood vessels that carry blood in the papillae of the skin) of a glomerulus from the kidney of a mouse. The hemoglobin-containing red cells appear deeply gray and homogeneous because they contain no nuclei. Blood present in the capillary loop filters materials across the thin cellular processes of the endothelium (the gray amorphous basement membrane which surrounds the cells) and between the foot processes of specialized cells (podocytes) that line the urinary space. Magnification: x14,000.