The integumentary System I
Touch your fingertips, your arm, and your face. The soft tissue
you feel is the outermost layer of your skin. Skin is the largest
2'
organ of your body. It is part of the integumentary (ihn teh gyuh
MEN tuh ree) system, which includes all the external coverings
of the body, including the skin, nails, and hair.
Functions of the Integumentary System
Recall that skin is part of your body's first line of defense. It
helps protect your body from harmful substances in the external
environment. It keeps your body from drying out in sunlight and
wind. Skin also protects the cells and tissues under the skin from
damage. Too much exposure to the Sun can damage skin. The
damage can result in sun burns or skin cancer. Skin can be
protected by using sun block and regulating the amount of time
it is exposed to the Sun.
Pore
Close your eyes and feel the surface of your desk and the
objects on top of it. Even with your eyes closed, you can tell the
difference between the desk, a book, paper, and pencils. You can
feel these differences because your skin has special cells called
sensory receptors that detect texture. Sensory receptors also
Sweat
detect temperature and sense pain. The more sensory receptors
gland
there are in an area of skin, the more sensitive it is.
Figure 10 During exercise, sweat
evaporates and blood vessels
enlarge. This releases thermal
energy.
Skin helps control body temperature. When you exercise, sweat
comes from tiny holes, or pores, on the skin's surface. Sweating is
one way skin lowers your body temperature, as shown in Figure 10.
As sweat evaporates, excess thermal energy leaves the body and
the skin cools. Another way that skin lowers body temperature is
by releasing thermal energy from blood vessels. Has your face
ever tffrned red while exercising? This happens because blood
e two
I
ys';skinhelps
control body
k
temperature.
vessels near the skin's surface dilate, or enlarge.
If your skin is exposed to sunlight, it can make vitamin D. Your
body needs vitamin D to help it absorb calcium and phosphorus,
which are needed for healthy bones. Your skin is not the only
u
o
_=
source of vitamin D. Vitamin D is usually added to milk, and it is
found naturally in certain types of fish.
0
Normal cellular processes produce waste products. The skin
helps eliminate these wastes. Water, salts, and other waste products are removed through the pores. This removal occurs all the
time, but you might only notice it when you sweat during
exercise.
452 Chapter 11
You shed about 600,000 flakes of skin ever
You get an entirely new layer of skin about every
20-30 days.
Epidermis
Dermis
tFatty layer
[
Figure 11 Skin has three layers, each with different functions.
Structures of the Skin
The skin that you see and feel on your body is the outermost
layer of skin. Below it are two other layers of skin. These layers,
12. Why is fiexib ty of
shown in Figure 11, differ in structure and function.
the skin important?
Epidermis
The epidermis (eh pub DUR mus) is the outermost layer of skin
and the only layer that comes into direct contact with the outside
environment. The epidermis is tough but thin. The epidermis on
your eyelids is thinner than a sheet of paper. Cells of the epidermis are constantly shed and replaced by new cells. One important function of the epidermis is the production of melanin
(MEH luh nun). Melanin is a pigment that protects the body by
absorbing some of the Sun's damaging ultraviolet rays.
Dermis
Below the epidermis is the dermis. The dermis is a thick layer
of skin that gives skin strength, nourishment, and flexibility. The
dermis contains sweat glands, blood vessels, nerves, hair follicles,
and muscles, as shown in Figure 11. When the muscles in the
dermis contract, you get goose bumps.
\
Fatty Layer
The innermost layer of skin insulates the body, acts as a protective padding, and stores energy. This layer is sometimes called
the fatty layer. It can be very thin or very thick, depending on its
location on the body.
,.
Lesson 11:1 Transport and Defense A53