Understanding the urinary tract
There are two kidneys, one on each side of the tummy (abdomen). They make urine which drains down tubes called ureters into the bladder. Urine is stored in the bladder. It is passed out through a tube (the urethra) which carries urine from the bladder when we go to the toilet.
What causes a urine infection?
Most urine infections are caused by germs (bacteria) which come from your own bowel. They cause no harm in your bowel but can cause infection if they get into other parts of your body. Some bacteria lie around your back passage (anus) after you pass a stool (faeces). These bacteria can sometimes travel to your urethra (the tube from the bladder that passes out urine) and into your bladder. Some bacteria thrive in urine and multiply quickly to cause infection.
Women are more prone than men to urine infections, as their urethra is shorter and opens nearer the anus. Pregnant women are also more prone than non-pregnant women to urine infections. This is partly due to the hormonal changes of pregnancy which affect the urinary tract and tend to slow down the flow of urine. It also may be that the enlarged womb (uterus) presses on the bladder and prevents it draining as well. If urine does not drain quickly from the bladder, germs are more able to multiply and cause an infection.
Less commonly there may be other causes of a urine infection. If you have to have a tube (called a catheter) passed into your bladder, it is easier for germs to directly reach your bladder, and this may make urine infection more likely. Occasionally for people whose immune systems are not working well, the infection may spread through the bloodstream rather than up the urinary tubes.
Did you find this information useful?
- Management of suspected bacterial urinary tract infection in adults; Scottish Intercollegiate Guidelines Network - SIGN (updated guidelines 2012)
- Guidelines on Urological Infections; European Association of Urology (2015)
- Urinary tract infection (lower) - women; NICE CKS, July 2015 (UK access only)
- Vazquez JC, Abalos E; Treatments for symptomatic urinary tract infections during pregnancy. Cochrane Database Syst Rev. 2011 Jan 19 (1):CD002256. doi: 10.1002/14651858.CD002256.pub2.
- Schneeberger C, Geerlings SE, Middleton P, et al; Interventions for preventing recurrent urinary tract infection during pregnancy. Cochrane Database Syst Rev. 2012 Nov 14 11:CD009279. doi: 10.1002/14651858.CD009279.pub2.