Download Structure and Movement The Skin Functions of the Skin

Structure and Movement
The Skin
Functions of the Skin
When you touch your face or arm, you are touching the
outer layer of your skin. Skin is the largest organ of the body.
It is part of the integumentary (ihn teh gyuh MEN tuh ree)
system. The integumentary system is made up of all of the external
coverings of the body, including the skin, nails, and hair. Like your
bones and muscles, skin has many different functions in
your body.
Protection
Skin covers your bones and muscles. Skin protects them
from the outside environment. It keeps your body from
drying out in sunlight and wind. Skin also protects the cells
and tissues under the skin from damage. Skin keeps dirt,
bacteria, viruses, and other substances from entering your
body.
Imagine you closed your eyes and felt two objects—a
brick and a piece of paper. You would be able to feel the
difference. The brick would feel rough, and the paper would
feel smooth. Your skin has sensory receptors that detect
texture. Sensory receptors in the skin also detect temperature
and sense pain. The more sensory receptors there are in an
area of skin, the more sensitive the skin is.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Sensory Response
Temperature Regulation
Skin helps control body temperature. Skin has tiny holes,
or pores, on its outer surface. When you exercise, sweat
comes from these pores. Sweating is one way that skin
maintains normal body temperature. As sweat evaporates,
excess thermal energy leaves the body and the skin cools.
Another way the skin maintains body temperature is by
releasing thermal energy from blood vessels. When your
body temperature begins to increase, such as when you are
exercising, blood vessels near the skin’s surface dilate, or
enlarge. This increases the surface area of the blood vessels
and releases more thermal energy.
Production of Vitamin D
If your skin is exposed to sunlight, it can make vitamin D.
Your body needs vitamin D to help it absorb calcium and
phosphorus. Vitamin D also helps bones grow.
Elimination
Normal cellular processes produce waste products. The
skin helps eliminate, or get rid of, some of these wastes.
Water, salts, and other waste products are removed through
the pores of the skin. Elimination occurs all the time, but
you probably only notice it when you sweat.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Structures of the Skin
The skin that you see and feel on your body is the outermost layer of your skin. Below it are two other layers of skin.
Each layer, as shown in the figure below, has a different
structure and function.
You shed about 600,000 flakes of skin every hour.
You get an entirely new layer of skin about every
20–30 days.
The fatty layer acts
as a shock absorber,
protecting the body
from injury.
Pore
Melanin
Epidermis
Sweat
gland
Nerve
Blood
vessels
Oil gland
Hair
follicle
Muscle
Your body’s dermis contains about
three million sweat glands.
Dermis
Fatty layer
Epidermis
The epidermis (eh puh DUR mus) is the outermost layer of skin
and the only layer in direct contact with the outside environment. The
epidermis is thin but tough. The epidermis on your eyelids
is thinner than a sheet of paper. Cells of the epidermis are
constantly shed, or gotten rid of, 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 tissue that gives skin strength, nourishment, and flexibility. The
dermis contains sweat glands, blood vessels, nerves, hair
follicles, and muscles. When the muscles in the dermis
contract, you get goose bumps.
Fatty Layer
The innermost layer of skin is sometimes called the fatty
layer. It insulates the body, keeping it warm. It also acts as a
protective padding and stores energy. This layer can be thin
or very thick, depending on where it is on the body.
Skin Injuries and Repair
Bruises
A bruise is an injury where blood vessels in the skin are broken, but
the skin is not cut or opened. The broken blood vessels release
blood into the surrounding tissue, forming the bruise.
Bruises usually change color as they heal. This change in
color is due to chemical changes in the blood under the
skin’s surface.
Cuts
When you break one or more layers of skin, a cut results.
Cuts often cut blood vessels, too. Blood that flows from a cut
usually thickens and forms a scab over the cut. The scab
helps keep dirt and other substances from entering the body.
Skin heals by making new skin cells that repair the cut.
Some cuts are too large to heal naturally. If that happens,
stitches might be needed to close the cut while it heals.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Skin is often injured because it is exposed to the outside
environment. You might have injured your skin by falling
down or bruising it. Your body has different ways to repair
skin. The type of repair depends on the type of injury and
how serious it is.
Burns
A burn is an injury to your skin or tissues that can be
caused by touching hot objects. Touching extremely cold
objects, chemicals, electricity, radiation (such as sunlight), or
friction (rubbing) can also cause burns. The three degrees, or
levels, of burns are described in the table below.
Burn Type
Description
Symptoms
Healing Time
First-degree
burn
damages top
layer of skin
pain, redness,
swelling
5–7 days
without
scarring
Second-degree
burn
damages top
and lower
layers of skin
pain, redness,
swelling,
blistering
2–6 weeks with
some scarring
Third-degree
burn
damages all
three layers of
skin and sometimes the tissue
below skin
black or white
charred skin,
might be numb
as a result of
damaged
nerves
several months
with scarring,
might need
surgery
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Healthy Skin
One way to keep your skin healthy is to protect it from
sunlight. The ultraviolet (UV) rays in sunlight can cause
permanent damage to the skin. Damage to the skin can
include dry skin, wrinkles, and skin cancer. You can protect
your skin from the UV rays in sunlight by using sunscreen.
You can also wear clothing, such as a hat or long-sleeved
shirt, to protect your skin.
Another way to keep your skin healthy is to eat a
balanced diet. You can also use gentle soaps to clean your
skin and lotion to keep your skin moist.
The Skin and Homeostasis
You have read that the skin can make vitamin D and that
it protects the body from outside substances. Both of these
functions help regulate the body’s internal environment.
The skin also works with other body systems to maintain
homeostasis. The skin and circulatory system help cool the
body when it becomes overheated. The skin also works with
the nervous system and muscular system to help the body
react to stimuli. For example, if you touch a hot pan,
receptors in your skin sense pain. This triggers nerve cells to
send a message to your brain. Your brain then sends a
message to your muscles to move your hand away.