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🫀anatomy and physiology ii review

Juxtamedullary nephron

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

A juxtamedullary nephron is a type of nephron in the kidney characterized by its long loop of Henle that extends deep into the medulla. This structure plays a crucial role in concentrating urine and regulating water balance in the body. The juxtamedullary nephron is essential for maintaining proper osmotic balance due to its ability to create a hyperosmotic environment in the renal medulla, which aids in the reabsorption of water from urine.

5 Must Know Facts For Your Next Test

  1. Juxtamedullary nephrons make up about 15-20% of all nephrons in the kidneys, while the majority are cortical nephrons.
  2. The long loops of Henle in juxtamedullary nephrons enable them to generate a greater osmotic gradient, allowing for more efficient water reabsorption.
  3. These nephrons play a critical role during dehydration, as they help conserve water and produce concentrated urine.
  4. The vasa recta, a specialized set of blood vessels, surround the loops of Henle in juxtamedullary nephrons, facilitating the exchange of water and solutes.
  5. The macula densa, part of the juxtaglomerular apparatus, monitors sodium concentration in the distal convoluted tubule and regulates blood pressure through renin secretion.

Review Questions

  • How do juxtamedullary nephrons contribute to urine concentration compared to cortical nephrons?
    • Juxtamedullary nephrons have longer loops of Henle that extend deep into the medulla, creating a more significant osmotic gradient than cortical nephrons. This gradient allows for enhanced reabsorption of water, which leads to more concentrated urine. In contrast, cortical nephrons have shorter loops and are primarily involved in the initial filtration process and less in concentrating urine.
  • Discuss the role of the vasa recta associated with juxtamedullary nephrons and how it influences kidney function.
    • The vasa recta are specialized blood vessels that supply juxtamedullary nephrons, playing a vital role in maintaining the osmotic gradient established by their long loops of Henle. By allowing countercurrent exchange, these vessels help preserve the concentration gradient in the renal medulla, which is crucial for water reabsorption. This interaction ensures that the kidneys can effectively concentrate urine and manage fluid balance within the body.
  • Evaluate the significance of juxtamedullary nephrons during periods of dehydration and their impact on overall homeostasis.
    • During dehydration, juxtamedullary nephrons are essential for conserving water and maintaining homeostasis by producing highly concentrated urine. Their ability to create a strong osmotic gradient enables effective reabsorption of water back into circulation. This process helps regulate blood volume and pressure while ensuring that essential electrolytes remain balanced. The functioning of these nephrons becomes critical to prevent dehydration-related complications, thus playing a significant role in overall fluid homeostasis.