M em branes • Figure 3.28
There are three major types of membranes: mucous, serous, and synovial.
Mucous membranes line
body cavities that open
to the outside.
b. Serous membrane
Serous membranes line
cavities that do not open
directly to the outside.
Membranes Cover or Line Parts
of the Body
Membranes are flat sheets of pliable tissue that cover
or line a part of the body. An epithelial membrane is
composed of an epithelial layer and an underlying con-
nective tissue layer. The principal epithelial membranes
of the body are mucous membranes, serous membranes,
and the cutaneous membrane or skin. The skin will be
discussed in detail in Chapter 4. Another type of mem-
lines joints and contains con-
nective tissue but no epithelium. Let’s look at the various
types of membranes (Figure 3.28).
A mucous membrane (
), or mucosa (
), lines a body cavity that opens directly to the out-
side. Mucous membranes line the entire digestive system,
respiratory system, and reproductive system and much of
the urinary system. The epithelial layer of a mucous mem-
brane secretes mucus, which has the following functions:
Prevents cavities from drying out
Traps particles in the respiratory passageways
Lubricates and absorbs food as it moves through the
Secretes digestive enzymes
The connective tissue layer of the mucous membrane (are-
olar connective tissue) helps bind the epithelium to the
underlying structures, provides it with oxygen and nutri-
ents, and removes wastes via its blood vessels.
A serous membrane, or serosa (
), lines a
body cavity that does not open directly to the outside,
82 CHAPTER 3
Cells and Tissues