This week we are going to learn about
skin!
I thought that this background kind of looked like a close-up
view of skin,
so I chose to stick with it for this entire unit!
You have already learned about the epidermis. And
you have found out that the dermis is made up of dense, irregular connective tissue.
Once two or more tissues come together for a common function, that is an organ;
therefore skin is considered an organ of your body. In this week's web pages, you
will learn about the details of the composition of this organ. You will also learn
about what it does for our bodies and how it can repair after injury.
Welcome to the first organ we're studying!
Some details of the skin tissues and the hypodermis are
offered for you in this web page. In order to find out more about the accessory
organs, function, and repair of skin you will have to follow the links at the top of this
page.
Note that by "accessory organs" of skin, I
mean hair, nails, glands, and sensory endings.
Skin = epidermis + dermis
The hypodermis is not officially considered a
part of skin. But it always lies below it.
About the
dermis (click to see an image of skin)...
You already know that the dermis is made up of dense irregular
connective tissue. Here are some other facts about the dermis:
 | The dermis contains blood vessels
|
Blood vessels run through the
dermis... of course, you knew this because connective tissues in general
are highly vascularized. In the dermis, the blood vessels supply both the dermis and the epidermis with nutrients. In order to
supply the epidermis, the blood vessels run all the way to the most superficial aspect
of the dermis. Arteries and veins are the blood vessels indicated in the figures in
your book-- you will learn more about these next semester... It is customary to draw
arteries as red and veins as blue.
The dermal blood vessels have a role in temperature regulation, as
you will see on the "Skin Functions" page.
| Fingerprints are due to dermal papillae
|
The most superficial aspect of the dermis is thrown into ridges.
These ridges are called dermal papillae. Because the
epidermis lies right on top of the dermal papillae, it is forced to follow their
curvature. Thus, we have fingerprints (and skin prints all over).
Here are a fun
website and a more
informative website that tell about fingerprints.
| The dermis contains the nerve endings for skin
sensation
|
There are three types of nerve endings: Meissner's
corpuscles, Pacinian corpuscles, and free nerve endings.
These nerve endings enable us to sense light touch, deep pressure, pain, and
temperatures (hot or cold). Meissner's corpuscles are for light touch and lie
immediately beneath the basement membrane of the epidermis. Pacinian corpuscles are
for deep pressure, and lie deeper in the dermis, even into the hypodermis. Free
nerve endings are for pain and temperature, and these endings lie at the superficial
aspect of the dermis-- they may even send tiny little processes into the epidermis (REALLY
tiny).
For another drawing/photo of these items, check out Figures 12.1 and
12.2 on pages 434 - 435. If you read about these items at all in chapter 12, keep in
mind that "sensory nerve fibers" only means the process of the touch or pressure
nerve that eventually ends in either Meissner's or Pacinian corpuscles.
We will come back to learn more about these when we get to chapter 12.
| The dermis contains exocrine glands
|
You can find out more details about this in the "Skin Glands" web page.
| Sweat Glands:
|
Sweat glands secrete wastes and are involved in temperature
regulation. Some sweat glands, in certain regions of the body, secrete smellier
wastes and contribute to our body odor.
| Sebaceous Glands:
These glands secrete oily waste, called sebum. This keeps our
skin smooth and protected.
|
| The dermis is where hair and nails are
produced
|
You can read more about this in the "Hair and Nails" web page.
| The dermis contains muscle
|
Small muscles called arrector pili, are found in
the dermis. These muscles, made up of smooth muscle, pull on the hairs in hairy skin
and make them stand up on end. This helps with temperature regulation in the body.
Click
here to see one!
| Dermal extracellular matrix fibers help
maintain skin structure
|
Elastin and collagen are important for maintaining the structure of
skin-- they keep it stretchable and help it hold up through numerous insults.
However, as extracellular fibers, they are vulnerable to damage. The sun and time
can wear away at these fibers. Also, through time, as we age, our fibroblasts do not
produce the same amounts of elastin and collagen. These problems show up as wrinkles
and older skin.
About the hypodermis...
| It contains much adipose tissue
|
The adipose tissue helps to insulate our bodies, preventing
excessive heat loss.
| The hypodermis contains larger blood vessels
|
The blood vessels in the hypodermis supply the blood vessels in the
dermis with blood. You probably are already aware of the fact that the blood vessels
in the hypodermis are larger-- have you ever noticed the difference in bleeding between an
entirely superficial cut and a deeper cut? Of course you have!
Funny bumpersticker I saw:
Did you ever stop to think... and forget to start again?
|
