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The urinary tract system is a group of organs of the body, which are responsible for the excretion of urine. In humans, the urinary system includes 2 kidneys, a pair of tube-like structures, called the ureters, which connect the kidneys to the bladder. The bladder is connected to the urethra, which delivers the urine to the outside of the body. The primary function of the urinary tract system is to remove substances from the blood, to form urine and help to regulate various metabolic processes.

(Click an organ above to see its description.)

Urethra

Function
In females, the urethra is a tube that conveys urine from the urinary bladder to the outside of the body. In males, the urethra also functions as a urinary canal and as a passageway for cells and secretions from various reproductive organs.

Structure
The wall of the urethra is lined with mucous membranes and contains a relatively thick layer of smooth muscle tissue. It also contains numerous mucous glands, called "urethral glands", that secrete mucous into the urethral canal. The smooth muscle fibers within the urethra run longitudinally. In females, the urethra is about 4 cm long. It passes forward from the bladder, descends below the symphysis pubis, and empties into the labia minor. Its opening is located above the vaginal opening and about 2.5cm below the clitoris. In males, the urethra can be divided into four sections: the prostatic urethra, the membranous urethra, the bulbar urethra and the penile urethra. The end of the urethra, called the urethral meatus, is located on the head (glans) of the penis.