Correct Option
The correct option is Vasa recta.
Explanation
The nephron, the functional unit of the kidney, is associated with a specific arrangement of blood vessels. The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule known as peritubular capillaries. The arrangement of these capillaries varies between cortical and juxtamedullary nephrons.
Detailed Analysis
- Vasa recta (Correct): In juxtamedullary nephrons, a minute vessel from the peritubular capillary network runs parallel to the long Loop of Henle, extending deep into the renal medulla. This U-shaped capillary network is called the vasa recta. It plays a critical role in the countercurrent mechanism, which is essential for concentrating urine.
- Afferent arteriole (Incorrect): This is the vessel that carries blood into the glomerulus for filtration. It does not run parallel to the Loop of Henle.
- Peritubular capillary (Incorrect): While the vasa recta originates from the peritubular capillaries, the term "peritubular capillaries" generally refers to the network surrounding the Proximal Convoluted Tubule (PCT) and Distal Convoluted Tubule (DCT) in the cortex. In cortical nephrons, the vasa recta is either absent or highly reduced.
- Venule (Incorrect): Venules are small blood vessels that collect blood from capillaries. While the vasa recta eventually drains into venules, the specific capillary network parallel to the Loop of Henle is distinctively termed the vasa recta.
Key Takeaway: The vasa recta is a specialized U-shaped capillary network found in juxtamedullary nephrons that runs parallel to the Loop of Henle and is fundamental to the maintenance of the medullary osmotic gradient.