Tissue Membranes

Tissue membranes are thin sheets of cells that cover and line body surfaces; there are four main types— mucous, serous, cutaneous, and synovial.

Mucous membranes line body cavities that open to the exterior, such as the respiratory tract. These membranes consist of a layer of epithelial cells over a supporting layer of areolar connective tissue, called lamina propria. Mucus or fluids such as urine help to moisten these membranes.

Serous membranes cover closed body cavities and the organs present within them. They comprise a layer of areolar connective tissue that supports the mesothelium. The mesothelium secretes serous fluid that lubricates the membrane's outer parietal and inner visceral layers.

The cutaneous membrane or skin is a dry and relatively waterproof covering for the body surface. It consists of the epidermis— a keratinized stratified squamous epithelium, attached to the underlying thick connective tissue layer called the dermis.

Synovial membranes line free-moving joints. They comprise areolar tissue and synoviocytes that secrete some of the components of synovial fluid— a lubricant for the articulating surfaces.