Structure and Movement

Transcription

1 Structure and Movement The Skin Key Concepts What does the skin do? How do the three layers of skin differ? How does the skin interact with other body systems? What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After 5. Skin helps regulate body temperature. 6. Skin is made of two layers of tissue. Main Idea and Details As you read, circle each heading that contains the word skin. Then, underline one sentence from each paragraph that follows that heading and its subheadings and teaches you something about skin. Reading Check 1. Explain What would happen to your body if you had no 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. Sensory Response 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. 236 Structure and Movement Reading Essentials

2 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. 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 days. The fatty layer acts as a shock absorber, protecting the body from injury. Sweat gland Nerve Blood vessels Hair follicle Pore Melanin Muscle Oil gland Your body s dermis contains about three million sweat glands. 2. Explain how the skin regulates body temperature. Visual Check 3. Name three structures found in the dermis layer of skin. Fatty layer Reading Essentials Structure and Movement 237

3 Math Skills The ratios 5 1 and 25 5 are equivalent, so they can be written as the proportion 5 1 = When ratios form a proportion, the cross products are equal. In the above proportion, 5 5 = You can use cross products to find a missing term. For example, if each 1 cm 2 of skin contains 300 pores, how many pores are there in 5 cm 2 of skin? 1 cm pores = n 5 pores cm2 1 n = n = 1500 pores 4. Using Proportions The palm of the hand has about 500 sweat glands per 1 cm 2. How many sweat glands would there be on a palm measuring 7 cm by 8 cm? 5. Contrast How do the skin s three layers differ? Make a half-book to record information about the different types of skin injuries and how the body repairs them. Skin Injuries and Repair Fat layer 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. 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 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. 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. 238 Structure and Movement Reading Essentials

4 Burns A 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 s. The three degrees, or levels, of s are described in the table below. Burn Type Description Symptoms Healing Time Reading Check 6. Identify Name three causes of s to the skin. First-degree damages top layer of skin pain, redness, swelling 5 7 days without scarring Second-degree Third-degree damages top and lower layers of skin damages all three layers of skin and sometimes the tissue below skin pain, redness, swelling, blistering black or white charred skin, might be numb as a result of damaged nerves 2 6 weeks with some scarring several months with scarring, might need surgery Visual Check 7. Explain If swelling and blisters appear on the surface of a ed area of skin, what degree of would it be? 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. 8. State Give two examples of how the skin interacts with other body systems to help maintain homeostasis. Reading Essentials Structure and Movement 239

5 Mini Glossary bruise: an injury where blood vessels in the skin are broken, but the skin is not cut or opened dermis: a thick layer of skin that gives the skin strength, nourishment, and flexibility epidermis (eh puh DUR mus): the outer layer of skin and the only layer in direct contact with the outside environment integumentary (ihn teh gyuh MEN tuh ree) system: made up of all of the external coverings of the body, including the skin, nails, and hair melanin (MEH luh nun): a pigment that protects the body by absorbing some of the Sun s damaging ultraviolet rays 1. Review the terms and their definitions in the Mini Glossary. Write two or three sentences that explain how the terms integumentary system, epidermis, dermis, and bruise are related. 2. Rewrite each phrase shown below in the correct part of the Venn diagram to compare and contrast the epidermis and the dermis. Both can be ed by extreme heat thick, middle layer of skin thin, top layer of skin 3. How does the number of sensory receptors affect an area of skin? What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? ConnectED Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson s resources. END OF LESSON 240 Structure and Movement Reading Essentials