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It seems that when a urinary tract infection happens, bacteria will cause inflammation to the lining of the urinary tract, and this will cause bleeding.

What is the exact process for the inflammation to cause bleeding? Is it because the lining expands too much and the tissue tears as a result? Or do bacteria interfere otherwise with the cells of the lining?

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The process by which bacteria in a UTI cause bleeding is that the bacteria cause inflammation of the lining of the urinary tract. The inflammation can cause the blood vessels in the lining to become more permeable, allowing blood to leak into the urine.

Inflammation causes blood vessels to become more permeable by increasing vasodilation, weakening the endothelium, and releasing inflammatory cytokines such as histamine and bradykinin. This leads to increased vascular leakage and disabled intercellular junctions, resulting in increased paracellular permeability (see references 1 and 2).

The increased permeability of the blood vessels can also make them more fragile and prone to rupture, leading to further bleeding. In addition, bacterial toxins produced during a urinary tract infection (UTI) damage the cells of the urinary tract lining by inducing host cell damage and releasing essential nutrients that promote bacterial survival. This can cause additional bleeding (see reference 3).

In some cases, severe UTIs can also spread to the bladder or kidney, where they can cause more tissue damage and increase the risk of bleeding, which makes treatment of these infection important (also reference 3).

References:

  1. Inflammation
  2. Vascular permeability—the essentials
  3. Urinary tract infections: epidemiology, mechanisms of infection and treatment options
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  • $\begingroup$ Upvoted this last Feb. but just noticed first sentence of last paragraph. Just fyi in case you want to correct it. Usually when we dx "UTI", it's a bladder infection. That's usually not serious at all (except to the poor soul who has it) and it's as common as dirt. When it's in another part of the urinary tract, while technically a UTI, it's either urethritis (far less common unless it's from an STD) or pyelonephritis (less common but still common.) I've only seen ureteritis once in my career. Delete once you've read this. $\endgroup$ Jun 24, 2023 at 2:06

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