The trigone is a muscular triangular area at the base of the bladder, located between the ureteral openings and the neck of the bladder.
The urethra is the hollow passage or tube, connected to the neck of the bladder, which carries the urine from the bladder to the outside of the body when you urinate. In women the urethra is short, but in men it is longer since it passes through the penis. In men, the urethra also transports seminal fluid to the outside of the body during ejaculation.
The urethral sphincter is a ring of two muscles which normally close off the bladder so that urine cannot escape. When you need to urinate and are ready to do so, the sphincter relaxes and allows the urine to pass out of the body.
The prostate is a walnut-shaped gland in men that surrounds the urethra at the bladder neck. The prostate supplies the fluid that mixes with semen to form seminal fluid.
The pelvic floor is a sling or hammock comprising a combination of muscles, ligaments and connective tissues that support the organs located in the pelvis including the bladder, rectum, uterus and vagina. It helps to hold these organs in place and to control the muscles that open and close the anus and urethra.
The balloon-like bladder has a wall made of muscle (the detrusor) that can stretch and contract as it stores and empties urine. The ureters carry urine into the bladder from the kidneys and, as the bladder fills, the muscle in the bladder wall relaxes to allow the bladder to expand. When you feel the need to urinate and go to the toilet, the detrusor muscle then contracts to expel the urine out of the bladder into the urethra where the sphincter muscle relaxes to allow the urine to pass through.