What are the membranes that line the body cavities opening to the outside of the body called?

Mucous membranes are specialized tissues that line body cavities and canals that open to the outside environment. They are critical for protecting the body and maintaining moisture in areas like the respiratory, digestive, and urogenital tracts. These membranes secrete mucus, which serves several functions, such as lubricating surfaces, trapping pathogens and particles, and keeping tissues moist.

In contrast, serous membranes line closed body cavities, like the abdominal and thoracic cavities, and do not open to the exterior. Synovial membranes line joints and produce synovial fluid, whereas connective membranes generally provide structural support but do not have the same specific function as mucous membranes. This distinction is essential in understanding how different membranes serve various roles in the body's overall protection and functionality.