What type of membranes line body cavities with no openings to the outside?

Serous membranes are specialized tissues that line body cavities that do not have openings to the exterior, such as those found in the thoracic and abdominal cavities. They serve a crucial function by providing a smooth, lubricated surface that allows for the easy movement of internal organs, reducing friction during activities like breathing and digestion.

These membranes consist of a layer of mesothelium (simple squamous epithelium) and underlying connective tissue, producing a serous fluid that fills the space between the visceral layer (which covers the organs) and the parietal layer (which lines the body cavity). This arrangement is vital for protecting organs and facilitating their movement.

In contrast, other types of membranes, such as mucous membranes, line cavities that open to the outside, including the respiratory, digestive, and urogenital tracts. Synovial membranes are found in joint cavities and line the surfaces of joints, producing synovial fluid for lubrication. Cutaneous membranes refer to the skin, which also provides an external barrier, rather than lining internal cavities.