You swallow a fish bone which pierces the mucus membrane of your oral cavity. which line of defense has been breached?

In the given case, the first line of defense is breached.  

The first line of defense involves the chemical and physical barriers, which are always prepared and ready to fight against the infections of the body. These are the surface barriers, which inhibit the admittance of pathogenic components.  

It comprises the tears, skin, cilia, mucus, urine flow, stomach acid, bacteria that are helpful, and white blood cells known as neutrophils.  

frogs. the lower the ph the higher the acid content. frogs have the highest tolerance in this scenario.