INTEGUMENTARY SYSTEM   The integumentary system, consisting of the skin, hair and nails, act as a barrier to protect the body from the outside world.  It also functions to retain body fluids, protect against disease, eliminate waste products, and regulate body temperature.   OBJECTIVES:  Identify the structures that make up the integumentary system.  Describe the functions of the skin.  Distinguish between the two layers that form the skin.  Compare the structure of hair with that of nails.  Identify two types of glands found in the skin, and describe their function.   1. SKIN AND ITS ACCESSORY ORGANS-THE HAIR, NAILS, AND A VARIETY OF GLANDS, MAKE UP THE INTEGUMENTARY SYSTEM.   2. The Skin is the human body's Largest Organs.   3. The word INTEGUMENT comes from a LATIN word that means to COVER.   4. THE MOST IMPORTANT FUNCTION OF THE INTEGUMENTARY SYSTEM IS PROTECTION.   5. IT PERFORMS THIS FUNCTION BY: (The FIVE Main Functions of the Integumentary System)       A. SERVING AS A BARRIER AGAINST INFECTION AND INJURY.       B. HELPING TO REGULATE BODY TEMPERATURE.       C. REMOVING WASTE PRODUCTS FROM THE BODY.       D. PROVIDING PROTECTION AGAINST ULTRAVIOLET RADIATION FROM THE SUN.       E.  PRODUCING VITAMIN D.   6. Because the skin contains several types of Sensory Receptors, it serves as the gateway through which Sensations such as PRESSURE, HEAT, COLD, AND PAIN ARE TRANSMITTED TO THE NERVOUS SYSTEM.   7.  The Skin is composed of Two Main Layers - The EPIDERMIS and DERMIS.    EPIDERMIS   1. The OUTER most layer of Skin is known as the EPIDERMIS.  It is composed of many sheets of Flattened, Scaly Epithelial Cells. This is a thin outer layer of skin.   2. Its layers are made of Mostly DEAD CELLS.   3. Most of the cells of the Epidermis undergo rapid cell division (MITOSIS).   4. As new cells are produced, they push Older cells to the surface of the skin.  The older cells become Flattened, Lose their Cellular Contents and begin  making KERATIN.   5. KERATIN IS A TOUGH FIBROUS PROTEIN AND FORMS THE BASIC STRUCTURE OF HAIR, NAILS, AND CALLUSES.   6. In animals keratin forms cow horns, reptile scales, bird feathers, and porcupine quills.   7. Eventually, the Keratin-producing Cells (KERATINCYTES) DIE AND FORM A TOUGH, FLEXIBLE WATERPROOF COVERING ON THE SURFACE OF THE SKIN.  Our thickest Epidermis in on the palms and soles.   8. THIS OUTER LAYER OF DEAD CELLS IS SHED OR WASHED AWAY ONCE EVERY 14 TO 28 DAYS.   9. The Epidermis contains MELANOCYTES, CELLS THAT PRODUCE MELANIN, A DARK BROWN PIGMENT.   10.  BOTH LIGHT SKINNED AND DARK SKINNED PEOPLE HAVE ROUGHLY THE SAME NUMBER OF MELANOCYTES, THE DIFFERENCE IN OUR SKIN COLOR IS CAUSED BY THE AMOUNT OF MELANIN THE MELANOCYTES PRODUCE AND DISTRIBUTE.   11.  The Amount of Melanin produced in Skin depends on TWO Factors - Heredity and the Length of Time the Skin is Exposed to Ultraviolet Radiation (Tanning).   12.  Melanin is important for protection, by absorption of Ultraviolet Radiation from the sun.  All people, but especially people with Light Skin, need to minimize exposure to the sun and protect themselves from its Ultraviolet Radiation, which can Damage DNA in Skin Cells and lead to deadly forms of Skin Cancer such as MELANOMA CANCER.   13.  THERE ARE NO BLOOD VESSELS IN THE EPIDERMIS, WHICH IS WHY A SMALL SCRATCH WILL NOT CAUSE BLEEDING.   DERMIS   1. THE DERMIS IS THE INNERMOST THICK LAYER OF THE SKIN COMPOSED OF LIVING CELLS.   2. The Dermis lies beneath the Epidermis and contains BLOOD VESSELS, NERVE ENDINGS, GLANDS, SENSE ORGANS, SMOOTH MUSCLES, AND HAIR FOLLICLES.   3. The Dermis helps us to control our body temperature:       A. On a cold day when the body needs to conserve heat, the Blood Vessels in the Dermis NARROW.       B. On hot days, the Blood Vessels WIDEN, warming the skin and increasing heat loss.   4. Tiny Muscle fibers attach to Hair Follicles contract and pull hair upright when you are cold or afraid, producing what is commonly called Goose Bumps.   5. Beneath the Dermis is the HYPODERMIS, (SUBCUTANEOUS LAYER), A LAYER OF FAT AND LOOSE CONNECTIVE TISSUE THAT INSULATES THE BODY AND ACTS AS AN ENERGY RESERVE.   6. The Dermis contains TWO major types of GLANDS: SWEAT GLANDS AND SEBACEOUS, OR OIL GLANDS.   7. These Glands PASS through the Epidermis and RELEASE THEIR PRODUCTS AT THE SURFACE OF THE SKIN.   8. SWEAT GLANDS PRODUCE THE WATERY SECRETIONS KNOWN AS SWEAT, WHICH CONTAINS SALT, WATER, AND OTHER COMPOUNDS.   9. These secretions are stimulated by nerve impulses that cause the production of sweat when the temperature of the body is raised.  They help to cool the body.   10. SEBACEOUS GLANDS, (OIL GLANDS) PRODUCE OILY SECRETION KNOWN AS SEBUM THAT SPREADS OUT ALONG THE SURFACE OF THE SKIN AND KEEPS THE KERATIN RICH EPIDERMIS FLEXIBLE AND WATERPROOF.   11. The production of Sebum is controlled by Hormones.   12. Oil Glands are usually connected by Tiny Ducts (Exocrine Glands) to Hair Follicles.  Sebum coats the surface of the skin and the shafts of hair, preventing excess water loss and lubricating and softening the Skin and Hair.   13. Sebum is mildly toxic to some Bacteria - protection.   14. If the Ducts of Oil Glands become clogged with excessive amounts of Sebum, Dead Cells, and Bacteria, the Skin disorder ACNE can result.   15. When first wearing new shoes, the skin of the foot may be subject to friction.  This will separate layers of Epidermis, or separate the Epidermis from the Dermis, and tissue fluid may collect, causing a BLISTER.   16. If the skin is subjected to pressure, the rate of mitosis will increase and create a thicker Epidermis; we call this a CALLUS.   BURNS   1. FLAMES, HOT WATER OR STEAM, SUNLIGHT, ELECTRICITY, OR CORROSIVE CHEMICALS MAY CAUSE BURNS OF THE SKIN.   2. THE SEVERITY OF BURNS RANGES FROM MINOR TO FATAL AND THE CLASSIFICATION OF BURNS IS BASED ON THE EXTENT OF DAMAGE.     3. FIRST-DEGREE BURN- ONLY THE SUPERFICIAL EPIDERMIS IS BURNED, AND IS PAINFUL BUT NOT BLISTERED. Causes death of Epidermal Cells.   4. SECOND-DEGREE BURN- DEEPER LAYERS EPIDERMIS ARE EFFECTED, COULD HAVE INFLAMMATION, BLISTERS, AND THE BURNED SKIN IS OFTEN PAINFUL.   5. THIRD DEGREE BURN- THE ENTIRE EPIDERMIS IS CHARRED OR BURNED AWAY, AND THE BURN MAY EXTEND INTO THE DERMIS.  OFTEN SUCH A BURN IS NOT PAINFUL AT FIRST, IF THE RECEPTORS IN THE DERMIS HAVE BEEN DESTROYED.   6. EXTENSIVE THIRD-DEGREE BURN- POTENTIAL LIFE-THREATENING BECAUSE OF LOSS OF SKIN, WITHOUT THIS NATURAL BARRIER, LIVING TISSUE IS EXPOSED TO THE ENVIRONMENT AND IS SUSCEPTIBLE TO INFECTION AND DEHYDRATION.   HAIR AND NAILS   1. HAIR IS PRODUCED BY CELLS AT THE BASE OF STRUCTURES CALLED HAIR FOLLICLES.   2. Hair Follicles are tubelike pockets of Epidermal Cells that extend into the Dermis.   3. Individual hairs are actually large columns of  DEAD Cells that have filled with KERATIN..   4. Rapid cell growth at the base of the Hair Follicle in the HAIR ROOT causes hair to grow longer.  Hair gets its color from Melanin.   5. Hair Follicles are in close contact with Sebaceous Glands.  The oily secretions of these Glands help maintain the condition of each individual hair.   6. Hair protects and insulates the body.   7. Most individual hairs grow for several years and then fall out.   8. NAILS GROW FROM AND AREA OF RAPIDLY DIVIDING CELLS KNOWN AS THE NAIL MATRIX or NAIL ROOT.   9. THE NAIL MATRIX IS LOCATED NEAR THE TIPS OF THE FINGERS AND TOES.   10. During Cell division, the Cells fill with Keratin and produce a tough, strong platelike nail that covers and Protects the tips of the fingers and toes.   11. Nails rest on a Bed of tissue filled with Blood Vessels, giving the nails a Pinkish Color.   12. Nails grow at a rate of 0.5 to 1.2 mm per day, with fingernails growing faster than toenails.