What part of the kidney is responsible for filtering blood?

The correct choice, nephrons, are the functional units of the kidney that play a crucial role in the filtration of blood. Each kidney contains approximately one million nephrons, and they are responsible for removing waste and excess substances from the blood while retaining necessary components like proteins and blood cells.

The filtering process occurs through the glomerulus, a network of tiny blood vessels where blood plasma is initially filtered. The filtered fluid then passes through various tubules within the nephron where further processing, reabsorption, and secretion occur, ultimately leading to the formation of urine.

In contrast, the renal pelvis is more of a collection area for urine before it moves to the ureter. The ureter itself is a tube that transports urine from the kidney to the bladder and is not involved in the filtering process. The medulla, which is the inner part of the kidney, contains structures associated with the nephrons and plays a role in urine concentration but does not filter blood directly. Thus, the nephrons are essential for kidney function and maintaining body fluid balance through their filtering capabilities.