Final answer:
The gland that surrounds the urethra below the bladder trigone is called the prostate gland.
Step-by-step explanation:
The gland that surrounds the urethra below the bladder trigone is called the prostate gland. The prostate gland is a walnut-sized organ located just below the bladder and surrounds the urethra. It secretes a slightly alkaline fluid that constitutes close to 30 percent of the total volume of semen.