Final answer:
Nephrons with long loops of Henle that extend into the renal medulla are called juxtamedullary nephrons. They are important for urine concentration, and they differ from cortical nephrons, which have shorter loops and are mostly situated in the renal cortex.
Step-by-step explanation:
Nephrons that are located close to the medulla of the kidney and have long loops of Henle that extend deep into the medulla are known as juxtamedullary nephrons. These nephrons play a crucial role in the concentration of urine. About 15 percent of nephrons in the kidneys are juxtamedullary nephrons. In contrast to cortical nephrons, which have short loops of Henle that mainly reside within the renal cortex, juxtamedullary nephrons have long loops of Henle that plunge into the renal medulla, making them essential for the kidney's ability to concentrate urine effectively.
The loop of Henle in the juxtamedullary nephrons is specialized for the recovery of Na+ and water, contributing to the urine concentration process. As the filtrate passes through the loop of Henle, the osmolarity changes, allowing the kidney to produce urine that can be either very concentrated or very dilute, depending on the body's needs. This function is supported by the vasa recta, which is part of the peritubular capillary network associated with juxtamedullary nephrons.