A frontal section through the cortex and medulla of an unembalmed kidney obtained from autopsy is shown here. The visible hilar region consists of minor calyces (grey/white) surrounded by yellow in appearance adipose tissue. The outer part of the kidney has a reddish-brown appearance; this is the cortex. It is easily distinguished from the inner portion, the medulla, which is further divided into an outer portion (OM), identified here by the presence of straight blood vessels, the vasa recta (VR), and an inner portion (IM), which has a lighter and more homogenous appearance. The medulla consists of renal pyramids, which have their base facing the cortex and their apex in the form of a papilla (P) is directed towards the hilum. The pyramids are separated, sometimes only partially as in this figure, by cortical material that is designated the renal columns (RC). The majority of the outer part of the pyramid on the left, has not been included in the plane of
Cortex and medulla, kidney, human, H&E ×20.
A histologic section including the cortex and part of the medulla is shown here. Located at the boundary between the two (partly marked by the dashed line) are numerous profiles of arcuate arteries (AA) and arcuate veins (AV ). The most distinctive feature of the renal cortex, regardless of the plane of section, is the presence of the renal corpuscles (RC). These are spherical structures composed of a glomerulus (glomerular vascular tuft) surrounded by the visceral the section. The papillae are free tips of the pyramids that project into the first of a series of large urine collecting spaces referred to as the minor calyces (MC); the inner surface of the calyx is white. The minor calyces drain into major calyces, and in turn, these open into the renal pelvis, which funnels urine into the ureter.
An interesting feature in this specimen is that the blood has been retained in many of the vessels, thereby allowing for visualization of several renal vessels in their geographic location. Among the vessels that can be identified in the cut face of the kidney shown here are the interlobular vessels (IV) within the cortex; the arcuate veins (AV) and the arcuate arteries (AA) at the base of the pyramids; the interlobar arteries (ILA) and veins (ILV) between renal pyramids and, in the medulla, the vessels going to and from the capillary network of the pyramid. The latter vessels, both arterioles and venules, are relatively straight and are designated collectively as the vasa recta (VR). (Specimen courtesy of Dr. Eric A. Pfeifer, Mayo Clinic, Rochester, MN).
and parietal epithelium of Bowman’s capsule. Also seen in the cortex are groups of tubules that are more or less straight and disposed in a radial direction from the base of the medulla (arrows); these are the medullary rays. In contrast, the medulla presents profiles of tubular structures that are arranged as gentle curves in the outer part of the medulla, turning slightly to become straight in the inner part of the medulla. The disposition of the tubules (and blood vessels) gives the cut face of the pyramid a slightly striated appearance that is also evident in the gross specimen (see figure above).
KEY AA, arcuate arteries AV, arcuate veins ILA, Interlobar artery ILV, Interlobar vein IM, inner medulla IV, interlobular vessels MC, minor calyx OM, outer medulla P, papilla RCol, renal column RC, renal corpuscles VR, vasa recta arrows, medullary rays dashed line, boundary between cortex and medulla