Which organ is primarily responsible for filtering blood in the urinary system?

The kidneys are the primary organs responsible for filtering blood in the urinary system. They perform the essential function of removing waste products and excess substances from the bloodstream, which are then excreted as urine. The kidneys continuously filter blood through a network of tiny structures called nephrons, where they regulate water, electrolytes, and other substances to maintain homeostasis in the body. This filtration process is crucial for detoxifying the blood and regulating blood pressure and fluid balance.

The other options do not serve the primary function of filtering blood. The ureters are tubes that carry urine from the kidneys to the urinary bladder, while the urinary bladder is a storage reservoir for urine before it is expelled from the body. The urethra is the tube through which urine is discharged from the bladder. None of these structures carry out the filtration process that the kidneys do.