= Juxtamedullary nephron
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.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section25.4: cortical and juxtamedullary nephrons]{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.
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