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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. |
Epithelial Membranes
Epithelial membranes consist of epithelial tissue and the
connective tissue to which it is attached. The two main types
of epithelial membranes are the mucous membranes and serous
membranes
Mucous Membranes
Mucous membranes are epithelial membranes that consist of
epithelial tissue that is attached to an underlying loose
connective tissue. These membranes, sometimes called mucosae,
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.
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 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 Membranes
Connective tissue membranes contain only connective tissue.
Synovial membranes and meninges belong to this category.
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.
Meninges
The connective tissue covering on the brain and spinal cord,
within the dorsal cavity, are called meninges. They provide
protection for these vital structures.
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