tIssUes, orGans, and orGan systeMs 75What are the functions of membranes?- Membranes protect and sometimes lubricate many body
surfaces and cavities. - The various epithelial membranes (mucous, serous, and
cutaneous) consist of epithelium overlying connective tissue.
Most contain glands. - Synovial membranes consist only of connective tissue. They line
joint cavities and produce fluid that lubricates the joint.
taKe-hoMe Messagethat prevent chafing between adja-
cent organs or between organs and
the body wall.
A third type of epithelial mem-
brane, the cutaneous membrane,
is familiar to you: It’s your skin (Fig-
ure 4.8C). This membrane’s tissues
are part of one of the body’s major
organ systems, the integumentary
system—the topic of Section 4.9.Membranes in joints
consist only of connective
tissue
A few membranes consist only of
connective tissue. These synovial
membranes (Figure 4.8D) line cavi-
ties of the body’s movable joints. They contain cells that
secrete fluid that lubricates the ends of moving bones or
prevents friction between a bone and a moving tendon.n Thin, sheetlike membranes cover many body surfaces and
cavities. Some provide protection. others both protect and
lubricate organs.A membrane is a thin, sheetlike tissue covering. In the body
we find two basic types—epithelial membranes and con-
nective tissue membranes.
in epithelial membranes, epithelium pairs
with connective tissue
Epithelial membranes consist of a sheet of epithelium atop
connective tissue. Examples are mucous membranes,
also called mucosae (singular: mucosa). These are the pink,
moist membranes lining the tubes and cavities of your
digestive, respiratory, urinary, and reproductive systems
(Figure 4.8A). Most mucous membranes, like the lining of
the stomach, contain glands and are specialized to secrete
substances, absorb them, or both. Some of the glands are
single cells. For example, goblet cells—so named because
their shape resembles a stemmed glass—secrete mucus.
Other mucous membranes have no glands. The mucous
membranes lining the urinary tract (including the tubes
that carry urine out) are like this.
Serous membranes are epithelial membranes that
occur in paired sheets. Imagine one paper sack inside
another, with a narrow space between them, and you’ll
get the idea. Serous membranes don’t have glands, but the
layers do secrete a fluid that fills the space between them.
Examples include the membranes that line the chest cav-
ity and enclose the heart and lungs (Figure 4.8B). Among
other functions, serous membranes help anchor internal
organs in place and provide lubricated smooth surfaces
tissue Membranes: thin, sheetlike Covers
Figure 4.8 Membranes cover many body surfaces and line body cavities. (A, B, D: © Cengage Learning; C: Fabian Cevallos/Sygma/Corbis)
A Mucous membrane B Serous membrane C Cutaneous membrane (skin) D Synovial membrane4.7
cutaneous membrane
Skin, a type of epithelial
membrane.
mucous membrane
Epithelial membrane that
lines tubes and cavities of
the digestive, respiratory,
urinary, and reproductive
systems.
serous membrane Type
of epithelial membrane that
occurs in paired sheets.
Serous membranes secrete
fluid that fills the space
between the sheets.
synovial membrane
Connective tissue mem-
brane that lines joint
cavities.Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).