The bladder is a distensible, hollow organ found in the pelvic region of the human body. Above it are two tube-like structures known as ureters that connect the bladder to each kidney. Below the bladder is a tube called the urethra that runs to the outside of the body.
Urine Storage
One of the main functions of the bladder is storage of urine that is produced by the kidneys. The urine runs through each of the ureters and is subsequently stored in the bladder for excretion. The bladder can hold varying amounts of urine in different individuals before it sends a signal the brain that urination will soon be necessary. The bladder has two sphincters known as the internal and external sphincters that open to expel the urine when the time has come. The external sphincter is different in that it is controlled voluntarily, which allows humans to urinate at our own convenience.
Urine Voiding
When the bladder fills up, it stretches and activates certain receptors in the bladder wall. This results in a reflex contraction of the bladder as well as opening of the internal sphincter. When urination is desired, the external sphincter is voluntarily opened, which results in expulsion of the urine into a structure known as the urethra. The urethra carries the urine to the outside of the body, where it is then excreted.
Antibacterial Properties
Urine that collects in the bladder has a risk of being colonized by bacteria with a risk of resulting infection. One of the primary ways the body prevents this infection is regular voiding of the urine, which obviously rids the body of any bacteria that might be collecting. In addition, the bladder has additional intrinsic antibacterial properties such as reduction in bacterial adherence to bladder wall and immune cell activity. These are some of the various ways that the bladder fights infection and bacterial colonization of the urine and bladder wall.
References
- Campbell-Walsh Urology, 9th Edition; Wein; 2007
- Urological Research; Antibacterial Activity of the Bladder Mucosa; Schlager, T et al. Volume 21; September 1993
