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A cortical nephron is a nephron whose renal corpuscle lies relatively superficially in the renal cortex and whose Loop of Henle is usually shorter than that of a juxtamedullary nephron. The contrast concerns the position of the corpuscle and the depth of the loop. It does not mean that every part of a cortical nephron is confined to cortical tissue.^[ref]

A useful reconstruction starts at a glomerulus and follows the continuous tubule. A loop can enter the outer renal medulla and return to the cortex even though its corpuscle is superficial. A single transverse section through a tubule does not reveal either its complete path or the depth of its originating corpuscle. Thus anatomical tracing provides information beyond simply counting circular profiles in a histology image.

Both nephron classes perform glomerular filtration and tubular processing. Their different arrangements contribute differently to the medullary concentrating system, rather than dividing the kidney into a filtration-only class and a concentration-only class. Studies sampling visible surface tubules must also identify which nephrons are accessible before treating those samples as representative of all nephron types.^[ref]

A juxtamedullary nephron is a nephron whose renal corpuscle lies in the deep renal cortex, near its boundary with the renal medulla, and whose long Loop of Henle extends into the medulla. “Juxtamedullary” describes the location of the corpuscle relative to that boundary; it does not place the corpuscle at the renal papilla. A more superficial cortical nephron generally has a shorter loop.^[ref]

The long loop brings tubular fluid through different levels of the medullary concentrating environment. The associated renal vasa recta supply blood while supporting countercurrent exchange, and the loop's segment-specific transport contributes to countercurrent multiplication. The same anatomical arrangement connects local membrane transport to the whole kidney's ability to conserve water.

For a reconstruction exercise, mark the position of one renal corpuscle, then follow its tubule rather than classifying it from a single cross-section. A deep-running loop can belong to a corpuscle that remains in cortical tissue. Conversely, a superficial tubular sample alone does not tell an experimenter how deeply the loop runs. Anatomical tracing therefore supplies information that a concentration measurement at one site cannot.