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Summary Outline
Introduction (p. 117)

An organ is formed by two or more tissue types grouped together and performing specialized functions. The skin, the largest organ in the body, is part of the integumentary system.

Skin and Its Tissues (p. 117)

Skin is a protective covering, helps regulate body temperature, retards water loss, houses sensory receptors, synthesizes various biochemicals, and excretes wastes. It is composed of an epidermis and a dermis separated by a basement membrane. Beneath the skin is the subcutaneous layer that binds the skin to underlying organs, stores fat, and contains blood vessels that supply the skin.

  1. Epidermis

    1. The epidermis is stratified squamous epithelium that lacks blood vessels.

    2. The deepest layer of the epidermis, called the stratum basale, contains cells that divide.

    3. Epidermal cells undergo keratinization as they mature and are pushed toward the surface.

    4. The outermost layer, called the stratum corneum, is composed of dead epidermal cells.

    5. The epidermis protects underlying tissues against water loss, mechanical injury, and the effects of harmful chemicals.

    6. Melanin protects underlying cells from the effects of ultraviolet light.

    7. Melanocytes transfer melanin to nearby epidermal cells.

    8. Melanin provides skin color.


      All people have about the same number of melanocytes.


      Skin color is due largely to the amount of melanin and the distribution and size of pigment granules in the epidermis.


      Environmental and physiological factors, as well as genes, influence skin color.

  2. Dermis

    1. The dermis binds the epidermis to underlying tissues.

    2. Dermal blood vessels supply nutrients to all skin cells and help regulate body temperature.

    3. Nerve cell processes are scattered throughout the dermis.


      Some dermal nerve cell processes carry impulses to muscles and glands of the skin.


      Other dermal nerve cell processes are associated with sensory receptors in the skin, and carry impulses to the brain and spinal cord.

    4. The dermis also has hair follicles, sebaceous glands, and sweat glands.

Accessory Structures of the Skin (p. 122)
  1. Nails

    1. Nails are protective covers on the ends of fingers and toes.

    2. Specialized epidermal cells that are keratinized make up nails.

    3. The keratin of nails is harder than that produced by the skin's epidermal cells.

  2. Hair follicles

    1. Each hair develops from epidermal cells at the base of a tubelike hair follicle.

    2. As newly formed cells develop and grow, older cells are pushed toward the surface and undergo keratinization.

    3. Hair color is determined by genes that direct the amount of eumelanin or pheomelanin produced by melanocytes associated with hair follicles.

    4. A bundle of smooth muscle cells is attached to each hair follicle.

  3. Sebaceous glands

    1. Sebaceous glands are usually associated with hair follicles.

    2. Sebaceous glands secrete sebum, which helps keep the skin and hair soft and waterproof.

  4. Sweat glands

    1. Each sweat gland is a coiled tube.

    2. Sweat is primarily water but also contains salts and wastes.

    3. Eccrine sweat glands respond to elevated body temperature; apocrine glands respond to emotional upset.

Regulation of Body Temperature (p. 125)

Regulation of body temperature is vital because heat affects the rates of metabolic reactions. Normal temperature of deeper body parts is close to a set point of 37°C (98.6°F).

  1. When body temperature rises above the normal set point, dermal blood vessels dilate and sweat glands secrete sweat.

  2. When body temperature drops below the normal set point, dermal blood vessels constrict and sweat glands become inactive.

  3. If body temperature continues to drop, skeletal muscles involuntarily contract.

Healing of Wounds (p. 125)

Skin injuries trigger inflammation. The affected area becomes red, warm, swollen, and tender.

  1. Dividing epithelial cells fill in shallow cuts in the epidermis.

  2. Clots close deeper cuts, sometimes leaving a scar where connective tissue replaces skin.

  3. Granulations form in large, open wounds as part of the healing process.

Page 130
exercise Chapter Assessments

    6.1 Introduction

  1. Two or more types of tissues grouped together and performing specialized functions defines a(n) . (p. 117)

    1. organelle

    2. cell

    3. organ

    4. organ system

    5. organism

  2. The largest organ(s) in the body is (are) the . (p. 117)

    1. liver

    2. intestines

    3. lungs

    4. skin

    5. brain

  3. 6.2 Skin and Its Tissues

  4. Functions of the skin include . (p. 117)

    1. retarding water loss

    2. body temperature regulation

    3. sensory reception

    4. excretion

    5. all of the above

  5. Describe how skin plays a role in the production of vitamin D. (p. 117)

  6. The epidermis is composed of layers of tissue. (p. 117)

  7. The layer of epidermal cells contains older keratinized cells and dead cells. (p. 119)

    1. stratum corneum

    2. stratum lucidum

    3. stratum granulosum

    4. stratum spinosum

    5. stratum basale

  8. Discuss the function of melanin, other than providing color to the skin. (p. 119)

  9. List and describe the influence of each factor affecting skin color. (p. 120)

  10. The dermis is composed primarily of what kind of tissue? (p. 122)

  11. 6.3 Accessory Structures of the Skin

  12. Describe how nails are formed, and relate the structure of nails to their function. (p. 122)

  13. Distinguish between a hair and a hair follicle. (p. 122)

  14. Sebaceous glands are glands that secrete . (p. 124)

  15. Compare and contrast eccrine and apocrine sweat glands. (p. 124)

  16. 6.4 Regulation of Body Temperature

  17. Explain how body heat is produced. (p. 125)

  18. Explain how sweat glands help regulate body temperature. (p. 125)

  19. Describe the body's responses to decreasing body temperature. (p. 125)

  20. 6.5 Healing of Wounds

  21. Explain how the healing of superficial breaks in the skin differs from the healing of deeper wounds. (p. 125)

Page 131
activity Integrative Assessments/Critical Thinking

    OUTCOMES 5.3, 6.2, 6.4

  1. A premature infant typically lacks subcutaneous adipose tissue, and the small body has a relatively large surface area compared to its volume. How do these factors affect the ability of a premature infant to regulate its body temperature?

  2. OUTCOME 6.2

  3. Everyone's skin contains about the same number of melanocytes, even though people have many different skin colors. How is this possible?

  4. Which of the following would result in the more rapid absorption of a drug: a subcutaneous injection or an intradermal injection? Why?

  5. OUTCOMES 6.2, 6.5

  6. How is it protective for skin to peel after a severe sunburn?

  7. As a rule, a superficial partial-thickness burn is more painful than one involving deeper tissues. How would you explain this observation?

  8. OUTCOMES 6.2, 6.3, 6.4, 6.5

  9. What special problems would result from the loss of 50% of a person's functional skin surface? How might this person's environment be modified to partially compensate for such a loss?


Visit the text website at www.mhhe.com/shieress11 for additional quizzes, interactive learning exercises, and more.


Anatomy & Physiology REVEALED includes cadaver photos that allow you to peel away layers of the human body to reveal structures beneath the surface. This program also includes animations, radiologic imaging, audio pronunciation, and practice quizzing. To learn more, visit www.aprevealed.com.