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
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.
Mucous Membranes
Mucous membranes are epithelial membranes that consist of a mucousforming 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
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
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
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.
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 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.