The Urinary System

Learn about the Urinary System and the process of urination, also called micturition!

The Urinary system is made up by the urethra, the urinary bladder, ureters and the kidneys. The urethra is a narrow tube which connects the bladder to the body's environment. Sphincter muscles around the urethra partly controls the release of urine from the bladder and out of the body. When the bladder is empty these sphincters contract and the detrusor muscle is relaxed. When releasing urine the autonomic nervous system takes over and the sphincter relax while the detrusor muscle contracts.

The Bladder is an organ that is hollow so that it can hold urine, and expand with the filling of urine into the bladder. A smooth muscle known as the detrusor muscle is situated on the bladder. When the urine is released through the urethra the bladder collapses. Once the bladder contains about 300 mL (half the maximum size) nerves on the bladder starts to send messages to the brain via the spinal cord, creating an urge to urinate.

The Kidneys filter the blood and excrete urine. Via the ureters the urine passes to the bladder. Normally the kidneys will excrete about 1000-1500mL urine a day.