Pathophysiology
Clinical meaning
Urinary tract infections (UTIs) occur when pathogenic microorganisms colonise and multiply within the urinary tract. UTIs are classified anatomically: lower UTIs include cystitis (bladder infection) and urethritis (urethral infection), while upper UTIs refer to pyelonephritis (kidney infection). The distinction is clinically important because pyelonephritis carries significantly greater morbidity and can progress to urosepsis. The urinary tract has several defence mechanisms against infection. The unidirectional flow of urine physically flushes bacteria from the tract. The ureterovesical junction has a valve mechanism preventing reflux. Urine itself has antibacterial properties: low pH, high osmolality, high urea concentration, and the Tamm-Horsfall protein that binds bacteria. The bladder epithelium (urothelium) secretes IgA antibodies and antimicrobial peptides. Complete bladder emptying with each void is critical as residual urine serves as a growth medium. Most UTIs are ascending infections. Bacteria from the perineal and periurethral area ascend the urethra to the bladder. The female urethra is anatomically shorter (3-4 cm vs 20 cm in males) and located closer to the vaginal and rectal flora, explaining the dramatically higher UTI prevalence in women (50% of women will experience...