4.7 Tissue Membranes

Mucous Membranes

- Consists of epithelial cells, their basement membrane, a thick layer of loose connective tissue called the lamina propria, and sometimes a layer of smooth muscle cells. - Mucous membranes line cavities and canals that open to the outside of the body, such as the digestive, respiratory, excretory, and reproductive passages. - Many, but not all, mucous membranes contain goblet cells or multicellular mucous glands that secrete a viscous substance called mucus. - The functions of the mucous membranes vary, depending on their location, and include protection, absorption, and secretion. For example, the stratified squamous epithelium of the oral cavity performs a protective function, whereas the simple columnar epithelium of the small intestine absorbs nutrients and secretes digestive enzymes and mucus. - Mucous membrane also lines the nasal passages. When that membrane becomes inflamed, we experience the "runny nose" characteristic of the common cold or an allergy.

Serous membranes

- Consists of three components: a layer of simple squamous epithelium called mesothelium, its basement membrane, and a delicate layer of loose connective tissue. - Serous membranes line cavities, such as the pericardial, pleural, and peritoneal cavities, that do not open to the exterior. - Serous membranes do not contain glands, but they secrete a small amount of fluid called serous fluid, which lubricates the serous membranes, making their surfaces slippery. - Serous membranes protect the internal organs from friction, help hold them in place, and act as selectively permeable barriers to prevent large amounts of fluid from accumulating within the serous cavities.

Membrane

- Is a thin sheet of tissue that covers a structure or lines a cavity. - Most membranes are formed from a superficial epithelial tissue and the connective tissue on which it rests. - The skin, or cutaneous membrane, is the external membrane. - The three major categories of internal membranes are mucous, serous, and synovial membranes

Synovial membranes

- Is made up of only connective tissue. - Synovial membranes consist of modified connective tissue cells, either intermixed with part of the dense connective tissue of the joint capsule or separated from the capsule by areolar or adipose tissue. - Synovial membranes line freely movable joints. They produce synovial fluid, which is rich in hyaluronic acid, making the joint fluid very slippery, thus facilitating smooth movement within the joint.