Urinary System

**Urinary system**: The urethra is the only urinary structure that differs significantly between males and females, largely because of its dual role in males for transporting both urine and semen. The urethra originates from the trigone area at the base of the bladder. Urination is controlled by an involuntary internal sphincter of smooth muscle and a voluntary external sphincter of skeletal muscle. The shorter female urethra contributes to a higher incidence of bladder infections in females. In males, the urethra also receives secretions from the prostate gland, Cowper’s gland and seminal vesicles in addition to sperm. The bladder, largely retroperitoneal, can hold approximately 500–600 mL of urine. Micturition, the process of urinary voiding, involves both involuntary and voluntary actions. Voluntary control of micturition requires a mature and intact sacral micturition center and functional spinal cord. Loss of micturition control, known as incontinence, results in involuntary voiding when the bladder contains about 250 mL urine. The ureters, which are retroperitoneal, connect the renal pelvis of the kidneys to the trigone area at the base of the bladder. A thick muscular wall of longitudinal and circular smooth muscle in the ureters propels urine toward the bladder through peristaltic contractions. *LICENSES AND ATTRIBUTIONS CC licensed content, Shared previously, Virus Infections and Hosts, Authored by: OpenStax College. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/contents/0QN1UvTH@2.4:QeFp89FH@4/Gross-Anatomy-of-Urine-Transpo* ## Keywords excretory system wastes kidneys ureters bladder urethra