Membranes

1. Membranes Body membranes are thin sheets of tissue that cover the body, line body cavities, and cover organs within the cavities in hollow organs. They can be categorized into epithelial and connective tissue membrane. There are three types of epithelial membranes: 1. Mucous membranes 2. Serous membranes 3. The Cutaneous membrane There are two types of connective tissue membranes: 1. The Synovial membrane 2. Meningeal membranes

2. Epithelial Membranes Epithelial membranes consist of epithelial tissue and the connective tissue to which it is attached. The three main types of epithelial membranes are the mucous membranes, serous membranes and the cutaneous membrane. Mucous membranes exhibit a variety of covering epithelia, i.e., stratified squamous, simple columnar or pseudostratified columnar. These epithelia contain mucous producing cells. Mucous provides a physical barrier to microbes. These membranes line internal spaces of the body that open to the outside. Serous membranes line body cavities (peritoneum) and surround organs such as the lung (pleura) and heart (pericardium). The fluid produced by these membranes reduces friction between internal organs. The cutaneus membrane is the skin. This highly specialized membrane will be discussed more completely later in the course.

3. Mucous Membranes Mucous membranes are epithelial membranes that consist of a mucous-forming epithelium that is attached to an underlying areolar connective tissue. The connective tissue layer is called the lamina propria. These membranes line the body cavities that open to the outside. The entire digestive tract is lined with mucous membranes. Other examples include the respiratory, excretory, and reproductive tracts. Pseudostratified epithelium Lamina propria

4. Serous Membranes Serous membranes line body cavities that do not open directly to the outside, and they cover the organs located in those cavities. Serous membranes are covered by a single layer of squamous cells and a thin layer of serous fluid that is secreted by the epithelium. Serous fluid lubricates the membrane and reduces friction and abrasion when organs in the thoracic or abdominopelvic cavity move against each other or the cavity wall. Serous membranes have special names given according to their location. For example, the serous membrane that lines the thoracic cavity and covers the lungs is called pleura. Connective tissue Simple squamous

5. Cutaneous Membrane – The Skin The skin, a cutaneous membrane is covered with a stratified squamous epithelium, called the epidermis, which manufactures a tough, waterproof protein called keratin. The underlying layer of connective tissue is called the dermis. The dermis contains various nerve endings and glands manufacturing sweat and oil. The dermis is richly endowed with reticular fiber and collagen. The surface of the skin is dry. Stratified squamous Epithelium Dermis

6. Connective Tissue Membranes Connective tissue membranes contain only connective tissue. Synovial membranes and meninges belong to this category. Synovial membranes are located within the joint capsules of free moving joints of the body. These membranes produce synovial fluid which serves to lubricate the joint. The meninges are a series of three membranes that surround the brain and spinal cord. They protect these organs and keep them bathed in cerebrospinal fluid.

7. Synovial Membranes Synovial membranes are connective tissue membranes that line the cavities of the freely movable joints such as the shoulder, elbow, and knee. Like serous membranes, they line cavities that do not open to the outside. Unlike serous membranes, they do not have a layer of epithelium. Synovial membranes secrete synovial fluid into the joint cavity, and this lubricates the cartilage on the ends of the bones so that they can move freely and without friction.

8. Meninges The meninges are three connective tissue membranes that lie just external to the brain and spinal cord. From external to internal, the meningeal layers are the Dura mater, the Arachnoid and the Pia mater.