Final answer:
The concentration of urine is determined by the reabsorption of water and solutes in the nephron tubules, adjustments made in the ascending loop of the nephron, and the role of the collecting ducts in maintaining normal osmolarity. ADH regulates urine concentration by stimulating the reabsorption of water through aquaporin channels in the collecting ducts.
Step-by-step explanation:
The extent to which urine becomes concentrated is determined by several factors. One major factor is the reabsorption of water and solutes in the nephron tubules. As the forming urine enters the ascending loop of the nephron, adjustments are made to the concentration of solutes, creating concentrated urine.
In addition, the collecting ducts play a major role in maintaining the body's normal osmolarity. If the blood becomes hyperosmotic, the collecting ducts recover more water to dilute the blood, resulting in concentrated urine. Conversely, if the blood becomes hyposmotic, the collecting ducts recover less water, leading to dilute urine.
This regulation of urine concentration is controlled by the hormone ADH (vasopressin), which is released by the posterior pituitary gland. ADH stimulates the insertion of aquaporin channels in the collecting ducts, allowing for the reabsorption of water and subsequent concentration of urine.