Urine is formed after a process of glomerular filtration in the kidneys. This urine is then conducted through the ureters, twin muscular tubes that connect the kidneys to the bladder, a storage chamber. The bladder is a muscular chamber that expands as urine fills it. From the bladder, a muscular tube, the urethra connects to the outside. The urethra , an internal sphincter at the junction of the urethra and bladder, and an external sphincter comprising the pelvic floor muscles, keep the urine in the bladder till it is ready to expel the urine. For urination, the bladder walls contract and the urethra and sphincter muscles relax, to allow urine to flow out from the urethra.
