Answer
An epithelial membrane may be considered an organ or a complex of two main tissues that covers and protects other tissue, or that lines cavities and provides lubrication and protection for other organs and tissues. There are three main types of epithelial membranes:cutaneous membranes, serous membranes and mucous membranes. All three types have two main types of cells--epithelial cells of the upper layer or layers of the membrane, and a lower connective tissues layer or lamina propria.
Work Step by Step
One classification of mucous membranes is serous type, cutaneous type and mucous secreting type.
An example of the cutaneous type is the skin. This comprises an superficial epidermal layer and a deeper connective tissue layer called the dermis. The epidermis consists of keratinized squamous epithelial cells. The epidermis binds and supports the dermis and contains its blood supply. Epithelial membranes may have dry or wet surfaces. In the case of the skin the superficial layer is usually dry. Serous epithelial membranes are wet. They continuously produce secretions of watery fluids of
varying viscosities, and compositions, but of lower viscosity than the viscosity of mucous secretions. Cavities that do not open to the exterior usually have serous linings. Thus the pleural cavity and the peritoneal cavity are lined with serous membranes. Visceral layers of serous membranes also cover the lungs, the heart and the GI organs, In addition serous membrane covers the mediastinum. The main function of the serous membrane is that of lubrication and reduction of friction. Mucous membrane is the second type of wet epithelial membranes. Mucous membranes also consist of epithelial outer layers and inner connective tissue layer. The epithelium may vary greatly from simple stratified , through pseudostratified columnar to ciliated pseudostratified columnar. As in the other types, there is always a lamina propria of connective tissue to stabilize the epithelium, and to provide the blood supply. Mucous secretions are produced by globlet and other cells of the epithelium. The viscous sticky fluid serves the body in several ways: mucous keeps the epithelial cells from becoming dry; it is a protection against germs; tight junctions of the epithelial cells guard the homeostatic integrity of the cytosol; respiratory tract mucus traps particles and keeps them out of the lungs. In addition, the mucous epithelium of the digestive tract secretes enzymes and absorbs digested nutrients. In general, mucous membranes line cavities that open directly to the exterior, for example GI tract, the respiratory tract and the urinary tract.
