Structure of the Skin

Objectives

When you have completed this section, you should be able to

• describe the histological structure of the epidermis, dermis, and subcutaneous tissue; and
• discuss the skin's color and markings.

Think About It

Dermal papillae are relatively high and numerous in palmar and plantar skin but low and few in number in skin of the face and abdomen. What do you think is the functional significance of this difference?

Think About It

An infant brought to a clinic shows abnormally yellow skin. How could you tell at a glance whether this was due to jaundice or to a large amount of carotene from strained vegetables in the diet?

Key Point Review

1. Name four types of epidermal cells and state the function of each.

2. List the five layers of epidermis in order from deep to superficial. What are the distinctive features of each?

3. What are the two layers of the dermis?

4. Name the pigments responsible for normal skin colors and explain how certain conditions produce symptomatic discoloration of the skin.

Functions of the Skin

Objectives

When you have completed this section, you should be able to

• describe the barrier functions of the skin; and
• describe the roles of the skin in synthesis, absorption, sensation, temperature control, and social interaction.

Key Point Review

5. How does the skin inhibit the survival of pathogens on its surface?

6. To what besides pathogenic organisms does the skin present a barrier?

7. Describe the step in the synthesis of vitamin D that occurs in the skin.

8. Describe two ways in which the skin helps to control body temperature.

Hair and Nails

Objectives

When you have completed this section, you should be able to

• describe the three types of hair;
• describe the histology of a hair and hair follicle;
• explain how hair grows and discuss the causes of baldness;
• discuss some theories of the purpose served by human hair; and
• describe the structure and functions of nails.

Think About It

A young man says his grandfather and father were both bald by the age of 35, so he expects to go bald at an early age as well. What is the flaw in his reasoning?

Key Point Review

9. Distinguish between vellus and terminal hair.

10. Describe the three regions of a hair along its length and the three layers of a hair in cross section.

11. State the function of the hair papilla, hair receptors, and arrector pili.

12. Give a reasonable explanation for the presence of scalp, nostril, and axillary hair and for eyebrows and eyelashes.

13. Define nail body, nail fold, eponychium, hyponychium, and nail matrix.

Cutaneous Glands

Objectives

When you have completed this section, you should be able to

• name two types of sweat glands and describe the structure and function of each;
• describe sebaceous and ceruminous glands; and
• distinguish between breasts and mammary glands and discuss their respective functions.

Key Point Review

14. How do merocrine and apocrine sweat glands differ in appearance and function?

15. What types of hair are associated with apocrine glands? Why?

16. What other type of gland is associated with a hair follicle? How does its mode of secretion differ from that of sweat glands?

17. Distinguish between the breasts and the mammary glands.

Integumentary Aging and Diseases

Objectives

When you have completed this section, you should be able to

• discuss the changes associated with puberty;
• discuss the changes associated with senescence;
• describe the three most common skin cancers; and
• describe the three classes of burns and discuss the most urgent concerns in burn treatment.

Think About It

Skin cancer is relatively rare among blacks. Why do you think this is so?

Think About It

A third-degree burn may be surrounded by painful areas of first- and second-degree burns, but the region of the third-degree burn is painless. Explain the basis for this lack of pain.

Key Point Review

18. What two hormones especially affect the integument at puberty? What effects do they have?

19. What types of cells are involved in the three types of skin cancer? Which of the three is most dangerous and what are its early warning signs?

20. Describe first-, second-, and third-degree burns.

21. What are the two most urgent concerns in the treatment of a burn patient? How do health-care workers deal with these concerns?

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