Question

fill in the blank question
mucous membranes secrete which coats the interior walls of structures open to the outside and protects the body from invasion by bacteria

Explanation:

Mucous membranes are known for secreting mucus. Mucus forms a protective layer on the inner - walls of body structures like the respiratory and digestive tracts that are open to the outside environment, acting as a barrier against bacteria.

Answer:

mucus