What structure is responsible for connecting the kidney to the bladder?

The structure responsible for connecting the kidney to the bladder is the ureter. The ureters are two muscular tubes that transport urine from the kidneys, where it is produced, to the urinary bladder, where it is stored before being expelled from the body. Each kidney has its own ureter; these tubes are essential for the urinary system's function.

The ureters are lined with smooth muscle, which helps propel urine through peristaltic contractions. This is important for ensuring that urine flows in one direction—from the kidneys to the bladder—without any backflow. The ureters play a vital role in maintaining the body’s fluid balance and excretion processes.

In contrast, functions of the other structures mentioned differ greatly from that of the ureters. The urethra is the tube responsible for carrying urine from the bladder to the outside of the body; the aorta is a major blood vessel that carries oxygenated blood from the heart to the rest of the body; and the renal capsule is a protective fibrous outer layer surrounding each kidney. Thus, focusing on the ureter clarifies its specific role in connecting the kidney to the bladder.