The effects of age on the integumentary system are often quite visible. Both layers of skin become thinner and more fragile as mitosis in the epidermis slows and fibroblasts in the dermis die and are not replaced;
repair of even small breaks or cuts is slower. The skin becomes wrinkled as collagen and elastin fibers in the dermis deteriorate. Sebaceous glands and sweat glands become less active; the skin becomes dry, and temper- ature regulation in hot weather becomes more diffi- cult. Hair follicles become inactive and hair on the scalp and body thins. Melanocytes die and are not replaced; the hair that remains becomes white. There is often less fat in the subcutaneous tissue, which may make an elderly person more sensitive to cold. It is important for elderly people (and those who care for them) to realize that extremes of temperature may be
harmful and to take special precautions in very hot or very cold weather.
SUMMARY
The integumentary system is the outermost organ system of the body. You have probably noticed that many of its functions are related to this location. The skin protects the body against pathogens and chemi- cals, minimizes loss or entry of water, blocks the harmful effects of sunlight, and produces vitamin D.
Sensory receptors in the skin provide information about the external environment, and the skin helps regulate body temperature in response to environ- mental changes. The subcutaneous tissue is a second- ary line of defense against pathogens, a site of fat storage and of the other metabolic functions of adi- pose tissue.
STUDY OUTLINE
The integumentary system consists of the skin and its accessory structures and the subcutaneous tissue. The two major layers of the skin are the outer epidermis and the inner dermis.
Epidermis—made of stratified squamous epithelium; no capillaries; cells called ker- atinocytes (see Figs. 5–1 and 5–2 and Table 5–1)
1. Stratum germinativum—the innermost layer where mitosis takes place; new cells produce ker- atin and die as they are pushed toward the surface.
Defensins are antimicrobial peptides produced when the skin is injured. Vitamin D is formed from cholesterol on exposure to the UV rays of sunlight.
2. Stratum corneum—the outermost layers of dead cells; keratin prevents loss and entry of water and resists entry of pathogens and chemicals.
3. Langerhans cells—phagocytize foreign material, take it to lymph nodes, and stimulate an immune response by lymphocytes.
4. Melanocytes—in the lower epidermis, produce melanin. UV rays stimulate melanin production;
melanin prevents further exposure of the stratum germinativum to UV rays by darkening the skin.
Dermis—made of irregular fibrous connec- tive tissue; collagen provides strength, and elastin provides elasticity; capillaries in the papillary layer nourish the stratum germina- tivum (see Fig. 5–1 and Table 5–2)
1. Hair follicles—mitosis takes place in the hair root;
new cells produce keratin, die, and become the hair shaft. Hair of the scalp provides insulation from cold for the head; eyelashes keep dust out of eyes;
nostril hairs keep dust out of nasal cavities (see Figs. 5–1 and 5–3).
2. Nail follicles—at the ends of fingers and toes; mito- sis takes place in the nail root; the nail itself is dead, keratinized cells. Nails protect the ends of the fin- gers and toes, enable the fingers to pick up small objects, and provide for efficient scratching (see Fig. 5–4).
3. Receptors—detect changes in the skin: touch, pres- sure, heat, cold, and pain; provide information about the external environment that initiates appro- priate responses; sensitivity of the skin depends on the number of receptors present.
4. Sebaceous glands—secrete sebum into hair follicles or to the skin surface; sebum inhibits the growth of bacteria and prevents drying of skin and hair.
5. Ceruminous glands—secrete cerumen in the ear canals; cerumen prevents drying of the eardrum.
6. Apocrine sweat glands—modified scent glands in axillae and genital area; activated by stress and emotions.
7. Eccrine sweat glands—most numerous on face, palms, soles. Activated by high external tempera- ture or exercise; sweat on skin surface is evaporated by excess body heat; potential disadvantage is dehy- dration. Excretion of small amounts of NaCl and urea is a very minor function.
8. Arterioles—smooth muscle permits constriction or dilation. Vasoconstriction in cold temperatures decreases dermal blood flow to conserve heat in the body core. Vasodilation in warm temperatures increases dermal blood flow to bring heat to the surface to be lost. Vasoconstriction during stress shunts blood away from the skin to more vital
organs, such as muscles, to permit a physical response, if necessary.
Subcutaneous Tissue—also called the superfi- cial fascia; connects skin to muscles (see Fig.
5–1 and Table 5–3)
1. Areolar tissue—also called loose connective tissue;
the matrix contains tissue fluid and WBCs that destroy pathogens that get through breaks in the skin; mast cells produce chemicals that bring about inflammation.
2. Adipose tissue—stores fat as potential energy;
cushions bony prominences; provides some insula- tion from cold. Other functions: contributes to appetite, the use of insulin, and the activation of WBCs.
102 The Integumentary System
REVIEW QUESTIONS
1. Name the parts of the integumentary system.
(p. 90)
2. Name the two major layers of skin, the location of each, and the tissue of which each is made.
(pp. 90, 95)
3. In the epidermis: (pp. 90, 93) a. Where does mitosis take place?
b. What protein do the new cells produce?
c. What happens to these cells?
d. What is the function of Langerhans cells?
4. Describe the functions of the stratum corneum.
(p. 90)
5. Name the cells that produce melanin. What is the stimulus? Describe the function of melanin (p. 94)
6. Where, on the body, does human hair have impor- tant functions? Describe these functions. (p. 95)
7. Describe the functions of nails. (p. 96)
8. Name the cutaneous senses. Describe the impor- tance of these senses. (p. 96)
9. Explain the functions of sebum and cerumen.
(pp. 96–97)
10. Explain how sweating helps maintain normal body temperature. (p. 98)
11. Explain how the arterioles in the dermis respond to cold or warm external temperatures and to stress situations. (p. 98)
12. What vitamin is produced in the skin? What is the stimulus for the production of this vitamin?
(p. 90)
13. Name the tissues of which the superficial fascia is made. Describe the functions of these tissues.
(p. 99)
FOR FURTHER THOUGHT
1. The epidermis has no capillaries of its own; the stratum corneum is made of dead cells and doesn’t need a blood supply at all. Explain why the epider- mis is affected by a decubitus ulcer. Name another group of people, besides hospital or nursing home patients, that is especially susceptible to developing pressure ulcers.
2. Going out in the sun stimulates quite a bit of activ- ity in the skin, especially on a hot summer day.
Describe what is happening in the skin in response to sunlight.
3. Ringworm is a skin condition characterized by
scaly red patches, often circular or oval in shape. It is not caused by a worm, but rather by certain fungi. What is the food of these fungi; that is, what are they digesting?
4. There are several kinds of cells in the epidermis.
Which cells exert their functions when they are dead? Which cells must be living in order to func- tion?
5. Wearing a hat in winter is a good idea. What hap- pens to the arterioles in the dermis in a cold envi- ronment? How does this affect heat loss? Is the head an exception? Explain.
104
CHAPTER 6
Chapter Outline Functions of the Skeleton Types of Bone Tissue Classification of Bones Embryonic Growth of Bone
Factors That Affect Bone Growth and Maintenance
The Skeleton Skull
Vertebral Column Rib Cage
The Shoulder and Arm The Hip and Leg Joints—Articulations The Classification of Joints Synovial Joints
Aging and the Skeletal System
BOX6–1 FRACTURES AND THEIR REPAIR
BOX6–2 OSTEOPOROSIS
BOX6–3 HERNIATED DISC
BOX6–4 ABNORMALITIES OF THE CURVES OF THE SPINE
BOX6–5 ARTHRITIS
Student Objectives