Polyarteritis nodosa

Light micrograph of a small muscular renal artery in polyarteritis nodosa. There is diffuse inflammation of the adventitia and marked thickening of the inner layers by loose connective tissue (arrows). The lumen (L) is significantly narrowed. Involvement of a vessel this large would be unusual in microscopic polyarteritis or granulomatosis with polyangiitis.

Light micrograph of a normal glomerulus. There are only one or two cells per capillary tuft, the capillary lumens are open, the thickness of the glomerular capillary wall (long arrow) is similar to that of the tubular basement membranes (short arrow), and the mesangial cells and mesangial matrix are located in the central or stalk regions of the tuft (arrows).