There are defense mechanisms in our body that protect us naturally from urinary tract infections and infections in general.

External defenses against urine infection

In order for the infection to develop, bacteria must be able to reach the urinary system.

Under normal conditions, they are stopped by some barriers encountered during their way to the bladder.

• pubic hair: the first obstacle encountered by bacteria is hair which represents a mechanical barrier for the passage of bacteria (it happens in the nose too where they prevent the entrance of foreign bodies in the nasal cavities or eyelashes)
• vulvo/vaginal bacterial flora: the extremely acid environment of the vulva, and especially of the vagina, favors the reproduction of the normal bacterial flora that prevents the proliferation of pathogenic microorganisms
• estrogen: in addition to low the pH, estrogen increases the ability of the vulvar and vaginal walls cells to prevent bacteria from “sticking” and, therefore, multiplying

Internal defenses against urine infection

Once these external barriers are overcomed, bacteria encounter numerous internal defenses:

• once bacteria reach the urethra, they still need to reach the bladder to cause cystitis. The urinary flow will hinder them by dragging them out
• if they manage to reach the bladder, its constant emptying is a defense mechanism that prevents bladder colonization
• the urothelium is composed of transition cells (which are constantly renewed) where microorganisms adhere. These cells have a very short life cycle and, when they die, they detach from the urothelium and are expelled with the urinary flow (the famous “desquamating epithelial cells” of the urine test) together with the germs adhered to them
• phagocyte cells are present in the urothelium; they can”eat” foreign agents. The urinary flow also drags these phagocytes with the germ they have “eaten” out
• Glycosaminoglycans (GAG) are present either in free form in the urine or as part of the urothelium. Those who are free, they join bacteria lectins preventing them from adhering to the bladder wall, being expelled by urination. GAGs that cover the urothelium, however, act as a shield against the infectious attack, protecting the delicate structures of the urothelium, preventing the inflammatory process and pain. In this case, bacteria remain attached to the GAGs, but don’t cause damage since they don’t reach the urothelial cells
• anti-reflux mechanisms prevent the urinary flow from going against the current, hindering the appearance of pyelonephritis
• urine contains bacteriostatic substances (which prevent bacterial multiplication) and bacteriolitics (which eliminate bacteria): organic acids, urea, ammonium, antibodies and lysozyme
• urine also contains a renal origin glycoprotein (Tamm Horsfall). It is the most abundant protein in urine and has a key role in the defense of the urinary tract. It attracts bacteria and adheres to their lectins preventing them from adhering to the bladder walls
• hormones also influence the bladder walls. Estrogens reduce the adhesiveness of urothelium

The absence or diminution of one or more body defense mechanisms facilitates the appearance of an infection of the urinary tract.