31 Skin: It Has You Covered-Mid

Skin It Has You Covered FOCUS Question What are the functions of your skin?

Your Amazing Skin! Skin Your body is covered in it. But what is skin, and why do you need it? Skin is the body's largest organ. An organ is a part of the body that has a specific and important function, such as your heart or lungs. Skin is a part of the excretory system, the system that rids the body of waste. But it does much more than that. Skin covers and protects your muscles, bones, blood vessels, and other parts of the body It protects your body. from the outside world. It keeps most fluids inside the body and germs out. It's a waterproof coat, and it keeps the body from getting too hot or too cold. Skin also allows us to sense the outside world. Math Moment Skin makes up about 15 of a person's body weight. If a person weighs 160 pounds. about how much does their skin weigh? (Hint: Multiply by 0.15 to solve the problem.)

On the Surface Skin covers your whole body, but it is thicker in some places and thinner in others. The area around your eyes and eyelids has the thinnest skin. The bottom of your feet and palms of your hands have the thickest skin. All skin is divided into three layers: the epidermis the dermis, and the hypodermis. The epidermis is the thin outer layer. It is composed of dead, flattened cells at the surface of the body Epidermis cells are constantly dying, flaking off, and being replaced by cells from below. Washing your skin helps remove the dead cells. We replace our epidermis about every thirty-five days.

Did you know that your nails and hair are part of your skin? Like all skin, they contain keratin, a type of protein produced in the epidermis. Keratin gives your body a strong, flexible covering. It helps make skin waterproof and keeps out germs and chemicals from the environment. The epidermis also produces a substance called melanin. Melanin protects skin from the harmful ultraviolet rays of the Sun. It also gives skin color. People born with darker skin produce more melanin than people with lighter skin When exposed to sunlight, your skin. produces more melanin and becomes a darker color. Do You Know? Freckles are small groups of cells that contain more melanin. People with lighter skin are more likely to form freckles.

Below the Surface The dermis is the middle layer of your skin (see diagram on page 3). It contains collagen, a type of tissue that connects the body together. Collagen makes skin firm but allows it to stretch and return to its shape like a rubber band. Tiny holes in the dermis, called pores, extend up into the epidermis. Some pores contain hair follicles—small tubes in the skin that hold each hair's root. Sebum is a kind of oil that moves up through the pores. Sebum keeps the skin moist, helps make it waterproof, and helps protect it from germs. Do You Know? Too much sebum can block pores with oil, dirt, and dead epidermis cells. and then become infected. The results are pimples Washing your skin to remove extra sebum can help keep pimples from forming.

Blood vessels in the dermis provide nutrients to the skin. These blood vessels, along with sweat glands, help control your body's temperature. When your body is too warm, the blood vessels expand to release heat at your body's surface. The sweat glands release water through pores. Water evaporating from your skin's surface cools the body. The dermis also has receptors and nerve endings that sense pressure, touch, pain, and temperature. The hypodermis (see diagram on page 3) is the deepest layer of skin. It attaches the dermis to muscles and bones. The hypodermis stores fat for quick energy. Fat also provides padding and insulates the body from temperature changes.