Inner area of the renal medulla, light micrograph. 0.5 micrometre thick section of material embedded in plastic, stained with toluidine blue. In the medulla, in addition to the collecting ducts, there are two other types of tubes that are difficult to distinguish between. The first, abundant here, is lined by a very squamous simple epithelium, in which the nuclei are prominent. They are Henle's loops. The second are capillaries whose thin endothelium is difficult to distinguish even at this magnification, although the presence of blood cells inside allows them to be easily identified.