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diagram of the structure of human skin

The Integumentary System


                    Did you know your skin is the largest organ of

                 your body? Did you know it does much more for

                 you than just cover your body?

      Skin, hair, nails, sweat glands and oil glands make up

your integumentary system. Much of the information you

receive about your environment comes through your skin—an organ that is only a few millimeters thick in most places.


Learning Objectives

By the end of this lesson, students should be able to:

  • List four functions of the skin.

  • Compare and contrast the epidermis and dermis layers of the skin.

  • Describe how the skin heals itself.

  • Explain the ABCDE warning signs of skin cancer.

  • List two ways to protect yourself from damaging effect of the UV rays of the sun.



dermis—the inner layer of the skin; it contains blood vessels, nerves, and sweat glands.


epidermis—the surface or outer layer of skin.


melanin—a chemical produced by melanocytes in the epidermis that give skin its color.


melanocytes—cells in the epidermis that produce melanin.


ultraviolet rays—damaging wavelengths of light from the sun and in tanning salon lights.


Your Skin

  Your skin is composed of two layers—the epidermis (outer layer) and the dermis (inner layer).

   The epidermis is a thin layer of cells that forms a protective layer over the inner dermis. It prevents water loss and prevents disease-causing organisms (pathogens) from entering your body through the skin.


   Melanocytes are cells in the epidermis that contain melanin, a chemical that absorbs light energy and helps protect against the damaging effects of ultraviolet (UV) rays from the sun. Melanin gives the skin color.

   New skin cells are made at the bottom of the epidermis. Older cells are sloughed off and new cells rise to take their places.


   The dermis is a much thicker layer that contains connective tissue, smooth muscle tissue, nerve tissue and blood. This layer also contains a layer of fat tissue which helps retain heat. Other structures include hair follicles, oil glands which secrete oils that keep hair and skin soft and waterproof, and sweat glands which excrete wastes and evaporate water and heat. Nails also come from this layer. Nerve cells in the dermis receive stimuli from the environment and sense pain, temperature and pressure.


   Your skin is much more than a covering for your body. It allows you to maintain a constant body temperature, retain moisture, keep out pathogens (disease-causing organisms), and heal injuries to the layers.


Let’s take a closer look at some of these important functions.
















Image: By Daniel de Souza Telles, File: HumanSkinDiagram.xcf,CC BY-SA 3.0,

Maintaining a Constant Body Temperature

   Your body can maintain almost the same temperature in many different environmental temperatures. It is basically the same normal temperature on a 90 degree summer day and a 40 degree day in the winter. Your temperature does not change with your environment.

How does your body maintain a constant temperature?


Fast Fact: Do snakes sweat? Cold-blooded animals cannot regulate their internal body temperature. Their temperature is, basically, the same as the environment. Cold-blooded animals use strategies such as lying in the sun to warm up or crawling into the shade to cool down. Some cold-blood animals hibernate through the winter.


   Your body heats up when you exercise or when temperatures in your environment increase. To cool you down and help your body maintain a constant body temperature, blood vessels in the skin dilate (get larger). Blood flow increases, and heat is lost through radiation. Glands in the dermis produce sweat if the body overheats. As the sweat evaporates, the body cools. When your internal temperatures are too cool, blood vessels in the skin constrict (get smaller). Blood flow decreases and heat is conserved in the body. These are major ways that humans maintain a constant, warm-blooded body temperature.


How does your skin heal itself?

   You can heal wounds or tears in your skin.  You probably take this for granted, but healing itself is a complicated process. Wounds become inflamed when blood vessels in the wounded tissue release blood and fluids. They fluids make the tissue swell, but they also deliver nutrients that help the healing process.

  Blood clots form through a complicated chemical process involving clotting factors in the blood and platelets (cells that help blood to clot). Cells flow to the injured area and form new fibers that bind the edges of the wound together. White blood cells fight bacteria that may be in the wound. A scab forms from the blood, cells, and dried fluid. The skin produced new skin cells under the scab and the scab falls off. If the wound was large or deep, the newly formed skin tissue may form a scar on the surface.


A Word About Skin Cancer

   Skin cancer can occur at any age. It used to occur more frequently in people over the age of 50 year, but in recent years it has been occurring more often in younger people. This is mostly likely because of the increase in tanning salons and the practice of tanning the skin year-round.

   There are now more cases of melanomas (skin cancers) in young people in their 20s and teen-age years.

   The main cause of skin cancer is exposure to damaging ultraviolet (UV) rays of the sun. Two types of UV rays, UVA and UVB rays, cause lasting damage to the skin. It is important to protect yourself from the harmful effects of UV rays.


Wear protective clothing if you are going to be outside for long periods of time. Use sunblock lotion with a high sun protective factor (SPF). Use extra caution if you will be outside during the peak midday sun hours.


 The American Academy of Dermatology (the study of the skin) has an easy way to remember the warning signs of skin cancer—the ABCDE’s!

Asymmetry - The growth is not symmetrical; one half does not match the other half.

Border - The border of a melanoma is irregular. Normal growths have regular borders.

Color - The color of a melanoma is uneven, having several colors throughout the same growth. It can also be intensely black with possibly a bluish tint.

Diameter - If the growth is larger than approximately a quarter of an inch.

Evolving- Any change in the size, shape, or color on your skin, or any new symptom such a bleeding or itching may be a warning sign. You should have your skin checked by a doctor!


Check for Understanding:

1.  What are the functions of the integumentary system?


2. Describe how the skin heals itself.


3. Explain the meaning of the ABCDEs of skin cancer.






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