one way is the nose ,the hair and the mucous in a person's noes prevents microbes from getting in by trapping them.
White blood cells
the diesease microbes stick to it before it enters the body!
They do not stop it but the mucus and motion of the cillia remove said microbes and dust should they get into the lungs.
Skin prevents microbes from entering your body...
Eat beans and fart regularily. Honestly , there's a constant exchange of microbes, bacteria, fluides and gasses between the insides and outsides of your body. A couple of microbes will not change a thing if your immune system is not compromised ...
whashing offten
Mucus, produced by the body's mucous membranes, is a sticky substance that can trap microbes like bacteria and viruses. This helps to prevent harmful pathogens from entering and infecting the body.
your stomach acids fight it off and they kill the microbes. in a way this is good and bad because if it kills the bad microbes then it kills the good microbes in our body aswell!
You can not. These organs have outlets to the outside and they can not be kept sterile. Your body does try to remove things by making mucous which more or less traps things like bacteria and even pollen and sweeps them away.
Microbes do often get into cuts, but at some point the cut will get sealed by clotting blood, or even by hardening lymph if there isn't enough blood. You can also put on a dressing (such as a band-aid) to keep out microbes.
In the human body, the primary line of defence is the skin. The skin stops most of the microbes from entering the interiors of the body. If however, the pathogen is able to gain access into the body, the lymphatic system comes into play. The pathogen is eliminated before it begins to cause any more trouble.
I'd assume your skin