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Structure and Function of the Urinary System

Ureter, Urinary Bladder, and Urethra

The ureters move urine to the urinary bladder by peristalsis.

The urinary bladder is a saclike organ that collects urine from the kidneys and is able to store it for a period of time until it is disposed of via urination. It serves as a temporary storage reservoir and sits just below the peritoneal cavity near the pelvic floor and behind the pubic bone. In women, it is positioned in front of the uterus, separated from the uterus by a space called the vesicouterine pouch.

The bladder is about the size of a grapefruit but can stretch as needed. The wall of the bladder is less than one-quarter of an inch thick. The walls are lined with a mucous membrane made up of transitional epithelial cells. Transitional epithelial cells have the ability to stretch to accommodate fluid accumulation in the bladder. When the bladder is empty, the mucosal lining has numerous folds called rugae. As the bladder fills with urine, the bladder walls expand. The typical human bladder generally holds around 10 to 16 ounces of fluid for up to five hours comfortably, but it can hold more for longer periods when needed.

Urine travels from the kidneys through the ureters. A ureter is a tube that carries urine from the kidney to the bladder. Urine collects in the bladder until such time as it is excreted during urination. During urination, the detrusor muscles of the bladder contract to squeeze the urine out. The opening at the bottom of the bladder empties urine into the urethra. The urethra is a tube that carries urine from the bladder to the external urethral orifice and out of the body.

Structure of the Urinary Bladder

Urine produced by the kidneys moves through the ureters and enters the bladder. The bladder serves as a temporary storage and collection area for urine. When ready to be released from the body, urine leaves the bladder through the urethra and is eliminated.