What is the skin and what does it do?
Every square inch of skin contains thousands of cells and hundreds of sweat glands, oil glands, nerve endings, and blood vessels. Skin is made up of three layers: the epidermis , dermis , and the subcutaneous tissue .
The upper layer of our skin, the epidermis, is the tough, protective outer layer. It is about as thick as a sheet of paper over most parts of the body. The epidermis has four layers of cells that are constantly flaking off and being renewed. In these four layers are three special types of cells:
 Melanocytes produce melanin , the pigment that gives skin its color. All people have roughly the same number of melanocytes; those of dark-skinned people produce more melanin. Exposure to sunlight increases the production of melanin, which is why people get suntanned or freckled.
 Keratinocytes produce keratin , a type of protein that is a basic component of hair and nails. Keratin is also found in skin cells in the skin's outer layer, where it helps create a protective barrier.
 Langerhans cells help protect the body against infection.
Because the cells in the epidermis are completely replaced about every 28 days, cuts and scrapes heal quickly.
Below the epidermis is the next layer of our skin, the dermis, which is made up of blood vessels, nerve endings, and connective tissue. The dermis nourishes the epidermis.
Without certain molecules in the dermis, our skin wouldn't stretch when we bend or reposition itself when we straighten up. These two types of fibers in the dermis, collagen and elastin , help the skin stretch and reposition itself when we move. Collagen is strong and hard to stretch and elastin, as its name suggests, is elastic. In older people, some of the elastin-containing fibers degenerate, which is one reason why the skin looks wrinkled
(most wrinkles are caused by sun exposure, though!).

The dermis also contains a person's sebaceous glands. These glands, which surround and empty into our hair follicles and pores, produce an oil called sebum (pronounced: seebum) that lubricates the skin and hair. Sebaceous glands are found mostly in the skin on the face, upper back, shoulders, and chest.
Most of the time, the sebaceous glands make the right amount of sebum. As a person's body begins to mature and develop during the teenage years, though, hormones stimulate the sebaceous glands to make more sebum. This can lead to acne when pores become clogged by too much sebum and too many dead skin cells. Later in life, these glands produce less sebum, which contributes to dry skin in older people.
The bottom layer of our skin, the subcutaneous tissue , is made up of connective tissue, sweat glands, blood vessels, and cells that store fat. This layer helps protect the body from blows and other injuries and helps it hold in body heat.
There are two types of sweat-producing glands. The eccrine glands are found everywhere in our bodies, although they are mostly in the forehead, palms, and soles of the feet. By producing sweat, these glands help regulate body temperature, and waste products are excreted through them.
The other type of sweat-producing gland, the apocrine glands, develop at puberty and are concentrated in the armpits and pubic region. The sweat from the apocrine glands is thicker than that produced by the eccrine glands. Although this sweat doesn't smell, when it mixes with bacteria on the skin's surface, it can cause body odor. A normal, healthy adult secretes about half a liter of sweat daily, but this may be increased by physical activity, fever, or a hot environment.

Questions: Answer on a piece of loose-leaf in your binder please.
1. What are the names of the three layers of skin?
2. What types of cells can you find in the top four layers of our skin? What role do these specialized cells play?
3. How often are epidermal cells replaced?
4. What is the function of the dermis?
5. What two fibers can you find in the middle layer of the skin? What role do these specialized fibers play?
6. What types of glands surround our hair follicles? What do these glands do?
7. Why do some teens have problems with acne? What types of glands are primarily responsible for this skin condition?
8. What is the bottom layer of the skin? Which four items make up this bottom layer?
9. What are eccrine glands and what do they do?
10. What are apocrine glands? Where are they located on our body?