Answer:
The correct answer is nephron loop. The mechanism that establishes the medullary osmotic gradient depends most on the permeability properties of the nephron loop.
Step-by-step explanation:
The nephron loop is the portion of the nephron that follows the proximal convoluted tubule. It is located mainly in the renal medulla. Water moves by osmosis thanks to an osmotic gradient, in other words, it moves from a space with a lower concentration of solutes (hypotonic solution) to a space with a higher concentration of solutes (hypertonic solution) to try to dissolve it. Among the functions of the nephron loop is the creation of the medullary osmotic gradient by the countercurrent multiplier mechanism. Osmolarity is an intensive property that requires one or more "sources" of osmoles, capable of creating a gradient. In the nephron loop there are several sources of this type: a) the system that transports NaCl in the thick portion of the ascending limb b) the passive Na + outflow from the thin portion of the ascending limb c) the Na + outflow and of urea from the collector.