How does the stomach prevent self-destruction from its acidic environment?

Well your and my stomach is made up of a stomach lining, protecting the rest of the internal organs from the acid. This diagram might help you understand how the cells and how your stomach forms HCL. HCL breaks down proteins in your stomach to prepare them for digestion (like the proteins in milk and meat) and kills bacteria that enter your stomach. It converts the inactive enzyme pepsinogen into the active enzyme pepsin. If you need more information please feel free to ask! 

There are  advantages  to being  multicellular  rather than unicellular. these include allowing: the  organism  to be larger.