system
Given the following post, respond as if you're commenting on Reddit:
human
By what mechanism(s) do our orifices resist infections that cuts in our skin do not have?
gpt
There's several:

* Friendly bacterial flora. They are capable of "out-competing" the bad bacteria in places like your mouth and anus. If the area is already colonized, it makes it that much more difficult for pathologic bacteria to colonize. A good example showing this is that if you wipe out someone's natural flora with antibiotics, they have a susceptibility to c. diff, which is a pathologic bacteria

* Physical mechanisms. The urethra is probably the best example of this. When you urinate, it flushes out bacteria. Things like a catheter that take away that natural flushing mechanism and can lead to UTIs. Women have a shortened urethra, which also leads them more susceptible to UTIs than men.

* Chemical mechanisms. Two examples of these are saliva in your mouth and vaginal secretions. They create a chemically unfavorable environment(pH, denaturing enzymes) that combat bacteria.

* Your actual cellular immune system. Places like your GI tract contains MALT, or Mucosa-associated lymphoid tissue. MALT is a highly concentrated area of immune tissue which helps fight pathologic bacteria

* Antibodies. Mucosal surfaces like the GI tract contain high concentrations of IgA immunoglobins, which bind to pathogens and prevent infections

Sterile environments like the bloodstream and unnatural orifices(skin cuts) lack some of these barriers which can lead to infection. edit: **Just some clarification -- the sterile parts of your body DO have protective systems(including antibodies and the cellular immune system), but lacks some of the other ones. This is why you don't get an infection every time you get a cut.**