What role do kidneys play in urine formation?

The kidneys play a crucial role in urine formation primarily by filtering and converting plasma into urine. This process begins in the nephron, the functional unit of the kidney, where the blood plasma is filtered through glomerular membranes. During this filtration process, various substances, including water, electrolytes, and waste products like urea, are removed from the blood.

Once the plasma is filtered, the kidneys engage in reabsorption and secretion processes. Reabsorption allows the body to reclaim necessary substances such as glucose and certain ions, while secretion helps eliminate additional wastes. The outcome of these processes is the formation of urine, which is then transported to the bladder for eventual elimination from the body.

The other options do not accurately represent the kidneys' primary function in urine formation. For instance, while the kidneys do have some role in detoxifying substances, this is not specifically about urine formation but rather about overall kidney function. Similarly, the kidneys do play a part in regulating blood pressure through fluid balance and the renin-angiotensin-aldosterone system, but this is not directly related to the formation of urine itself. Lastly, storage of urine occurs in the bladder, not in the kidneys. Overall, the focus on the kidneys converting plasma to