Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

Companies, 2004

The integumentary system consists

of the skin and accessorystructures

such as hair, nails, and glands. In-

tegumentmeans covering, and the in-

tegumentary system isfamiliar to most

people because it covers the outside of

the bodyand is easily observed. In addition,

humans are concerned with the appearance of

the integumentarysystem. Skin without blemishes is

considered attractive, whereasacne is a source of embarrassment for many

teenagers. The developmentof wrinkles and the graying or lossof hair is a sign

ofaging that some people ﬁnd unattractive. Because of these feelings, much

time, effort, and moneyare spent on changing the appearance of the integu-

mentarysystem. For example, people apply lotion to their skin, color their hair,

and trim their nails. Theyalso try to prevent sweating with antiperspirants and

bodyodor with washing, deodorants, and perfumes.

The appearance ofthe integumentary system can indicate physiological

imbalancesin the body. Some disorders like acne or warts affect just the in-

tegumentary system. Disorders of other parts of the bodycan be reﬂected

there, and thusthe integumentary system is useful for diagnosis. For example,

reduced blood ﬂow through the skin during a heartattack can cause a pale ap-

pearance, whereasincreased blood ﬂow asa result of fever can cause a ﬂushed

appearance. Also, the rashesof some diseases are very characteristic, such as

the rashesof measles, chicken pox, and allergicreactions.

Thischapter providesan overview of the integumentary system (144) and

an explanation ofthe hypodermis (144), the skin (145), and the accessory skin

structures(150). A summary of integumentary system functions (156) and the

effectsof aging on the integumentary system (157) are also presented.

Integumentary

System

Colorized scanning electron micrograph (SEM) of

the shaftof a hair protruding through the surface

of the skin. Note the ﬂat, scalelike epithelial cells

of the skin.

CHAPTER

Part 2 Supportand Movement

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

Companies, 2004

5. Excretion.Small amounts of waste products are lost through

the skin and in gland secretions.

1. Provide an example for each function of the integumentary

system.

Hypodermis

Objective

■ Describe the structure and function of the hypodermis.

Just as a house rests on a foundation,the skin rests on the

hypodermis (hı¯-po¯-der⬘mis), which attaches it to underlying

bone and muscle and supplies it with blood vessels and nerves (ﬁg-

ure 5.1).The hypodermis consists of loose connective tissue with

collagen and elastin ﬁbers.The main types of cells within the hypo-

dermis are ﬁbroblasts,adipose cells,and macrophages. The hypoder-

mis,which is not part of the skin, is sometimes called subcutaneous

(su˘b-koo-ta¯⬘ne¯-u˘s)tissue, or superﬁcial fascia (fash⬘e¯-a˘).

Approximately halfthe body’s stored fat is in the hypoder-

mis,although the amount and location vary with age, sex, and diet.

For example,newborn infants have a large amount of fat, which ac-

counts for their chubby appearance; and women have more fat

than men,especially over the thighs, buttocks, and breasts. Fat in

the hypodermis functions as padding and insulation and is respon-

Overview of the Integumentary

System

Objective

■ Describe the functions of the integumentary system.

Although we are often concerned with how the integumen-

tary system looks,it has many important functions that go beyond

appearance. The integumentary system forms the boundary be-

tween the body and the external environment,thereby separating

us from the external environment while allowing us to interact

with it.Major functions of the integumentary system include:

1. Protection.The skin provides protection against abrasion

and ultraviolet light.It also prevents the entry of

microorganisms and prevents dehydration by reducing

water loss from the body.

2. Sensation.The integumentary system has sensor y receptors

that can detect heat,cold, touch, pressure, and pain.

3. Temperature regulation.Body temperature is regulated by

controlling blood ﬂow through the skin and the activity of

sweat glands.

4. Vitamin D production.When exposed to ultraviolet light,

the skin produces a molecule that can be transformed into

vitamin D.

Part2 Supportand Movement144

Hairs

Sebaceous

gland

Arrector pili

(smooth muscle)

Hair follicle

Vein

Artery

Fat

Nerve

Sweat gland

Epidermis

Skin

Dermis

Hypodermis

(subcutaneous

tissue)

Figure 5.1

Skin and Hypodermis

The ﬁgure representsa block of skin (dermis and epidermis), hypodermis, and accessorystructures (hairs and glands).

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

Companies, 2004

Chapter 5 Integumentary System 145

sible for some of the differences in body shape between men and

women.

2. Name the types of tissue forming the hypodermis.

3. How is the hypodermis related to the skin?

4. List the functions of fat contained within the hypodermis.

Usesof the Hypodermis

The hypodermiscan be used to estimate total body fat. The skin is

pinched atselected locations, and the thickness of the fold ofskin and

underlying hypodermisis measured. The thicker the fold, the greater is

the amountof total body fat. Clinically, the hypodermisis the site of

subcutaneousinjections.

Skin

Objectives

■ Describe the parts of the skin and their functions.

■ Explain the factors affecting skin color.

The skin is made up of two major tissue layers.The dermis

(derm⬘is; skin) is a layer of connective tissue that is connected to

the hypodermis.The epidermis (ep-i-derm⬘is;on the dermis) is a

layer ofepithelial tissue that rests on the dermis (see ﬁgure 5.1). If

the hypodermis is the foundation on which the house rests, the

dermis forms most ofthe house, and the epidermis is its roof.

Dermis

The dermis is responsible for most ofthe structural strength of the

skin.It is connective tissue with ﬁbroblasts, a few adipose cells,and

macrophages. Collagen is the main connective tissue ﬁber,but

elastin and reticular ﬁbers are also present.Adipose cells and blood

vessels are scarce in the dermis compared to the hypodermis.Nerve

endings,hair follicles, smooth muscles, glands, and lymphatic ves-

sels are also in the dermis (see ﬁgure 5.1).The ner ve endings are

varied in structure and function:free ner ve endings for pain,itch,

tickle,and temperature sensations; hair follicle receptors for light

touch;pacinian corpuscles for deep pressure; Meissner’s corpuscles

for the ability to detect simultaneous stimulation at two points on

the skin;and Rufﬁni’s end organs for continuous touch or pressure

(see ﬁgure 14.1).Nerve endings are described in chapter 14.

Usesof the Dermis

The dermisis that part of an animal hide from which leather ismade. The

epidermisof the skin is removed, and the dermis is treated with

chemicalsin a process called tanning. Clinicallythe dermis in humans is

sometimesthe site of such injections as the tuberculin skin test.

The dermis is divided into two layers (see ﬁgure 5.1,and ﬁg-

ure 5.2):the deeper reticular (re-tik⬘u¯ -la˘r)layer and the more su-

perﬁcialpapil lary (pap⬘i-la¯r-e¯) layer. The reticular layer, which is

dense irregular connective tissue,is the main layer of the dermis. It

is continuous with the hypodermis and forms a mat of irregularly

arranged ﬁbers that are resistant to stretching in many directions.

The elastin and collagen ﬁbers are oriented more in some directions

than in others and produce cleavage,or tension,lines in the skin

(ﬁgure 5.3).Knowledge of cleavage line directions is important be-

cause an incision made parallel to the cleavage lines is less likely to

gap than is an incision made across them.The closer together the

edges of a wound, the less likely is the development of infections

and the formation ofconsiderable scar tissue.

Ifthe skin is overstretched, the dermis may rupture and leave

lines that are visible through the epidermis. These lines, called

striae(strı¯⬘e¯),or stretch marks,can develop on the abdomen and

breasts ofa woman during pregnancy.

The papillary layer derives its name from projections called

papillae (pa˘-pil⬘e¯) that extend toward the epidermis (see ﬁgure

5.2).The papillary layer is less dense than the reticular layer and is

sometimes called loose connective tissue because it has thin ﬁbers

that are somewhat loosely arranged.The papillar y layer also con-

tains a large number ofblood vessels that supply the overlying epi-

dermis with nutrients, remove waste products, and aid in

regulating body temperature.

5. Name and compare the two layers of the dermis. Which layer

isresponsible for most of the structural strength of the skin?

6. What are cleavage lines and striae?

Epidermis

The epidermis is stratiﬁed squamous epithelium, and it is sepa-

rated from the papillary layer of the dermis by a basement mem-

brane. The epidermis is not as thick as the dermis, contains no

blood vessels,and is nourished by diffusion from capillaries of the

papillary layer (see ﬁgures 5.1 and 5.2).Most cells of the epidermis

are called keratinocytes(ke-rat⬘i-no¯-sı¯tz) because they produce a

protein mixture called keratin (ker⬘a˘-tin).Keratinocytes are re-

sponsible for the structural strength and permeability characteris-

tics of the epidermis. Other cells of the epidermis include

melanocytes (mel⬘a˘-no¯-sı¯tz),which contribute to skin color,

Langerhans’ cells, which are part of the immune system (see

chapter 22), and Merkel’s cells,which are specialized epidermal

cells associated with nerve endings responsible for detecting light

touch and superﬁcial pressure (see chapter 14).

Cells are produced by mitosis in the deepest layers ofthe epi-

dermis.As new cells are formed, they push older cells to the surface

where they slough off,or desquamate (des⬘kwa˘-ma¯t).The outer-

most cells in this stratiﬁed arrangement protect the cells under-

neath, and the deeper replicating cells replace cells lost from the

surface.As they move from the deeper epidermal layers to the sur-

face, the cells change shape and chemical composition. This

process is called keratinization (ker⬘a˘-tin-i-za¯⬘shu˘n) because the

cells become ﬁlled with keratin.During keratinization, these cells

eventually die and produce an outer layer ofcells that resists abra-

sion and forms a permeability barrier.

Keratinization and Disease

The studyof keratinization is important because manyskin diseases

resultfrom malfunctions in this process. For example, large scalesof

epidermaltissue are sloughed off in psoriasis (so¯-rı¯⬘a˘-sis; see “Clinical

Focus: ClinicalDisorders of the Integumentary System” on p. 158). By

comparing normaland abnormal keratinization, scientistsmay be able

to develop effective therapies.

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

Companies, 2004

Although keratinization is a continual process,distinct tran-

sitional stages can be recognized as the cells change.On the basis of

these stages,the many layers of cells in the epidermis are divided

into regions, or strata (sing., stratum) (see ﬁgure 5.2 and ﬁgure

5.4).From the deepest to the most superﬁcial, these ﬁve strata are

observed:stratum basale, stratum spinosum, stratum granulosum,

stratum lucidum,and stratum corneum. The number of cell layers

in each stratum and even the number ofstrata in the skin var y,de-

pending on their location in the body.

Stratum Basale

The deepest portion of the epidermis is a single layer of cuboidal

or columnar cells,the st ratum basale (ba¯⬘sa˘-le¯) (see ﬁgures 5.2

and 5.4). Structural strength is provided by hemidesmosomes,

which anchor the epidermis to the basement membrane,and by

Part2 Supportand Movement146

desmosomes,which hold the keratinocytes together (see chapter

4).Keratinocytes are strengthened internally by keratin ﬁbers (in-

termediate filaments) that insert into the desmosomes. Ker-

atinocytes undergo mitotic divisions approximately every 19 days.

One daughter cell becomes a new stratum basale cell and divides

again,but the other daughter cell is pushed toward the surface and

becomes keratinized (ker⬘a˘-ti-nı¯zd). It takes approximately

40–56 days for the cell to reach the epidermal surface and

desquamate.

Stratum Spinosum

Superﬁcial to the stratum basale is the stratum spinosum (spı¯-

no¯⬘su˘m), consisting of 8–10 layers of many-sided cells (see ﬁg-

ures 5.2 and 5.4).As the cells in this stratum are pushed to the

surface, they flatten; desmosomes are broken apart, and new

Epidermis

Dermal

papilla

Epidermis

Papillary

layer of dermis

Reticular

layer

of dermis

Papilla

Stratum

corneum

Stratum lucidum

Stratum

granulosum

Stratum spinosum

Stratum basale

Dermal papilla

extending into

the epidermis

LM 500x

LM 40x

Figure 5.2

Dermisand Epidermis

(a) Photomicrograph ofdermis covered bythe epidermis. The dermis consists of the papillary and reticular layers. The papillary layer hasprojections called papillae that

extend into the epidermis. (b) Higher magniﬁcation photomicrograph ofthe epidermis resting on the papillarylayer of the dermis. Note the strata of the epidermis.

(a)

(b)

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

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Chapter 5 Integumentary System 147

desmosomes are formed. During preparation for microscopic

observation, the cells usually shrink from one another,except

where they are attached by desmosomes,causing the cells to ap-

pear spiny—hence the name stratum spinosum.Additional ker-

atin ﬁbers and lipid-ﬁlled,membrane-bounded organelles called

lamellar(lam⬘e˘-la˘r,la˘-mel⬘a˘r) bodies are formed inside the ker-

atinocytes. A limited amount of cell division takes place in this

stratum,and for this reason the stratum basale and stratum spin-

osum are sometimes considered a single stratum called the stra-

tum germinativum (jer⬘mi-na˘-tı¯v⬘u˘m). Mitosis does not occur

in the more superﬁcial strata.

Stratum Granulosum

Thestratum g ranulosum (gran-u¯-lo¯⬘su˘m) consists of two to ﬁve

layers ofsomewhat ﬂattened, diamond-shaped cells with long axes

that are oriented parallel to the surface ofthe skin (see ﬁgures 5.2

and 5.4).This str atum derives its name from the nonmembrane-

bounded protein granules of keratohyalin (ker⬘a˘-to¯-hı¯⬘a˘ -lin),

which accumulate in the cytoplasm ofthe cell. The lamellar bodies

ofthese cells move to the plasma membrane and release their lipid

contents into the intercellular space.Inside the cell, a protein enve-

lope forms beneath the plasma membrane.In the most superﬁcial

layers ofthe stratum granulosum, the nucleus and other organelles

degenerate,and the cell dies. Unlike the other organelles, however,

the keratin ﬁbers and keratohyalin granules do not degenerate.

Stratum Lucidum

The stratum lucidum (loo⬘si-du˘m) appears as a thin, clear zone

above the stratum granulosum (see ﬁgures 5.2 and 5.4) and con-

sists ofse veral layers ofdead cells with indistinct boundar ies.Ker-

atin ﬁbers are present,but the keratohyalin, which was evident as

granules in the stratum granulosum,has dispersed around the ker-

atin ﬁbers, and the cells appear somewhat transparent. The

stratum lucidum is present in only a few areas of the body (see

“Thick and Thin Skin”below).

Stratum Corneum

The last and most superﬁcial stratum of the epidermis is the stra-

tum corneum(ko¯r⬘ne¯-u˘m) (see ﬁgures 5.2 and 5.4). This stratum

is composed ofapproximately 25 or more layers of dead squamous

cells joined by desmosomes. Eventually the desmosomes break

apart,and the cells are desquamated from the surface of the skin.

Dandruff is an example of desquamation of the stratum corneum

of the scalp. Less noticeably,cells are continually shed as clothes

rub against the body or as the skin is washed.

The stratum corneum consists of corniﬁed cells, which are

dead cells with a hard protein envelope that are ﬁlled with the pro-

tein keratin. Keratin is a mixture of keratin ﬁbers and kerato-

hyalin. The envelope and the keratin are responsible for the

structural strength of the stratum corneum. The type of keratin

found in the skin is soft keratin.Another type of keratin, hard ker-

atin,is found in nails and the external parts of hair. Cells contain-

ing hard keratin are more durable than cells with soft keratin and

do not desquamate.

Surrounding the cells are the lipids released from lamellar

bodies. The lipids are responsible for many of the permeability

characteristics ofthe skin. Table 5.1 summarizes the structures and

functions ofthe skin and hypodermis.

PREDICT

Some drugsare administered by applying them to the skin (e.g., a

nicotine skin patch to help a person stop smoking). The drug diffuses

through the epidermisto blood vessels in the dermis. What kind of

substancescan pass easily through the skin by diffusion? What kind

have difﬁculty?

Thickand Thin Skin

When we say a person has thick or thin skin,we are usually refer-

ring metaphorically to the person’s ability to take criticism.How-

ever,all of us in a literal sense have both thick and thin skin. Skin is

classiﬁed as thick or thin on the basis of the structure of the epi-

dermis. Thick skin has all ﬁve epithelial strata, and the stratum

corneum has many layers of cells. Thick skin is found in areas

An incision made across

cleavage lines can gap,

increasing the time needed

for healing, and result in

increased scar tissue

formation.

An incision made parallel to cleavage

lines results in less gapping, faster

healing, and less scar tissue.

Figure 5.3

Cleavage Lines

The orientation ofcollagen ﬁbers producescleavage, or tension, lines in the skin.

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

Companies, 2004

subject to pressure or friction,such as the palms of the hands, the

soles ofthe feet, and the ﬁngertips. The papillae of the dermis un-

derlying thick skin are in parallel, curving ridges that shape the

overlying epidermis into ﬁngerprints and footprints.The ridges in-

crease friction and improve the grip ofthe hands and feet.

Fingerprintsand Criminal Investigations

Fingerprintswere ﬁrst used in criminal investigation in 1880 by Henry

Faulds, a Scottish medicalmissionary. Fauldsused a greasy ﬁngerprint

lefton a bottle to identify a thief who had been drinking puriﬁed alcohol

from the dispensary.

Thin skin covers the rest of the body and is more ﬂexible

than thick skin.Each stratum contains fewer layers of cells than are

found in thick skin;the stratum granulosum frequently consists of

only one or two layers ofcells, and the stratum lucidum generally

is absent.The dermis under thin skin projects upward as separate

papillae and does not produce the ridges seen in thick skin.Hair is

found only in thin skin.

The entire skin, including both the epidermis and the der-

mis,varies in thickness from 0.5 mm in the eyelids to 5.0 mm for

the back and shoulders.The terms thin and thick,which refer to the

epidermis only, should not be used when total skin thickness is

considered. Most of the difference in total skin thickness results

from variation in the thickness ofthe dermis. For example, the skin

ofthe back is thin skin, whereas that of the palm is thick skin; how-

ever,the total skin thickness of the back is greater than that of the

palm because more dermis exists in the skin ofthe back.

Part2 Supportand Movement148

In skin subjected to friction or pressure,the number of layers

in the stratum corneum greatly increases to produce a thickened

area called a callus(kal⬘u˘s).The skin over bony prominences may

develop a cone-shaped structure called a corn. The base of the

cone is at the surface,but the apex extends deep into the epidermis,

and pressure on the corn may be quite painful.Calluses and corns

can develop in both thin and thick skin.

7. From deepest to most superﬁcial, name and describe the

ﬁve strata of the epidermis. In which strata are newcells

formed bymitosis? Which strata have live cells, and which

have dead cells?

8. Describe the structural features resulting from

keratinization thatmake the epidermis structurallystrong

and resistantto water loss.

9. Compare the structure and location of thick skin and thin

skin. Ishair found in thick or thin skin?

Skin Color

Pigments in the skin, blood circulating through the skin,and the

thickness of the stratum corneum together determine skin color.

Melanin(mel⬘a˘-nin) is the term used to describe a group ofpig-

ments responsible for skin,hair, and eye color.Melanin is believed

to provide protection against ultraviolet light from the sun.Large

amounts of melanin are found in certain regions of the skin, such

as freckles,moles, nipples,areolae of the breasts,the axillae,and the

genitalia.Other areas of the body, such as the lips, the palms of the

hands,and the soles of the feet, contain less melanin.

Intercellular

lipids

Keratin

Lamellar body

releases lipids

Protein envelope

Keratohyalin

granules

Keratin fiber

Lipid-filled

lamellar body

Desmosome

Nucleus

Basement membrane

Hemidesmosome

5. Stratum corneum

Dead cells with a hard protein envelope;

the cells contain keratin and are surrounded

by lipids.

4. Stratum lucidum

Dead cells containing dispersed keratohyalin.

3. Stratum granulosum

Keratohyalin and a hard protein envelope

form; lamellar bodies release lipids; cells die.

2. Stratum spinosum

Keratin fibers and lamellar bodies accumulate.

1. Stratum basale

Cells divide by mitosis and some

of the newly formed cells become

the cells of the more superficial strata.

Superficial

Deep

ProcessFigure 5.4

EpidermalLayers and Keratinization

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Chapter 5 Integumentary System 149

In the production ofmelanin, the enzyme tyrosinase (tı¯⬘ro¯-si-

na¯s,tir⬘o¯-si-na¯s) converts the amino acid tyrosine to dopaquinone

(do¯⬘pa˘-kwin⬘o¯n,do¯⬘pa˘-kwı¯-no¯n). Dopaquinone can be converted to

a variety ofrelated molecules, most of which are brown to black pig-

ments,but some of which are yellowish or reddish.

Melanin is produced by melanocytes(mel⬘a˘-no¯-sı¯tz), irreg-

ularly shaped cells with many long processes that extend between

the keratinocytes of the stratum basale and the stratum spinosum

(ﬁgure 5.5). The Golgi apparatuses of the melanocytes package

melanin into vesicles called melanosomes (mel⬘a˘-no¯-so¯mz),

which move into the cell processes of the melanocytes. Ker-

atinocytes phagocytize (see chapter 3) the tips of the melanocyte

cell processes,thereby acquiring melanosomes. Although all ker-

atinocytes can contain melanin,only the melanocytes produce it.

Melanin production is determined by genetic factors,hor-

mones,and exposure to light. Genetic factors are primarily responsi-

ble for the variations in skin color between different races and

among people of the same race.The amount and t ypes of melanin

produced by the melanocytes,and the size, number,and distribution

of the melanosomes, is genetically determined.Skin colors are not

determined by the number ofmelanocytes because all races have es-

sentially the same number.Although many genes are responsible for

skin color,a single mutation (see chapter 29) can prevent the manu-

facture of melanin.Albinism (al⬘bi-nizm) usually is a recessive ge-

netic trait causing an inability to produce tyrosinase.The result is a

deﬁciency or absence ofpigment in the skin, hair, and eyes.

During pregnancy, certain hormones cause an increase in

melanin production in the mother,which in turn causes darkening

of the nipples, areolae, and genitalia. The cheekbones,forehead,

and chest also may darken,resulting in the “mask of pregnancy,”

and a dark line of pigmentation may appear on the midline of the

abdomen. Diseases like Addison’s disease that cause an increased

secretion ofcertain hormones also cause increased pigmentation.

Exposure to ultraviolet light darkens melanin already present

and stimulates melanin production,resulting in tanning of the skin.

The location ofpigments and other substances in the skin af-

fects the color produced.If a dark pigment is located in the dermis

or hypodermis, light reﬂected off the dark pigment can be scat-

tered by collagen ﬁbers ofthe dermis to produce a blue color. The

same effect produces the blue color of the sky as light is reﬂected

from dust particles in the air.The deeper within the dermis or hy-

podermis any dark pigment is located,the bluer the pigment ap-

pears because of the light-scattering effect of the overlying tissue.

This effect causes the blue color of tattoos,br uises,and some su-

perﬁcial blood vessels.

Carotene (kar⬘o¯-te¯n) is a yellow pigment found in plants

such as carrots and corn. Humans normally ingest carotene and

use it as a source ofvitamin A. Carotene is lipid-soluble, and, when

Table 5.1

Part Structure Function

Comparison of the Skin (Epidermis and Dermis) and Hypodermis

Epidermis Superficial part of skin; stratified squamous epithelium; Barrier that prevents water loss and the entry of

composed of four or five strata chemicalsand microorganisms; protects against

abrasion and ultraviolet light; produces vitamin D;

gives rise to hair, nails, and glands

Stratum corneum Most superficial strata of the epidermis; 25 or more Provisionof structural strength by keratin within cells;

layers of dead squamous cells prevention of water loss by lipids surrounding cells;

desquamation of most superficial cells resists abrasion

Stratum lucidum Three to five layers of dead cells; appears transparent; Dispersion of keratohyalin around keratin fibers

present in thick skin, absent in most thin skin

Stratum granulosum Two to five layers of flattened, diamond-shaped cells Production of keratohyalin granules; lamellar bodies

release lipids from cells; cells die

Stratum spinosum A total of 8–10 layers of many-sided cells Production of keratin fibers; formation of lamellar bodies

Stratum basale Deepest strata of the epidermis; single layer of cuboidal Production of cells of the most superficial strata;

or columnar cells; basement membrane of the melanocytes produce and contribute melanin,

epidermis attaches to the dermis which protects against ultraviolet light

Dermis Deep part of skin; connective tissue composed of two Responsible for the structural strength and flexibility

layers of the skin; the epidermis exchanges gases,

nutrients, and waste products with blood vessels in

the dermis

Papillary layer Papillae projects toward the epidermis; loose connective Brings blood vessels close to the epidermis; papillae

tissue form fingerprints and footprints

Reticular layer Mat of collagen and elastin fibers; dense, irregular Main fibrous layer of the dermis; strong in many

connective tissue directions; forms cleavage lines

Hypodermis Not part of the skin; loose connective tissue with Attaches the dermis to underlying structures; fat

abundant fat deposits tissue provides energy storage, insulation, and

padding; blood vessels and nerves from the

hypodermis supply the dermis

Seeley−Stephens−Tate:

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II. Support and Movement 5. Integumentary System

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large amounts ofcarotene are consumed, the excess accumulates in

the stratum corneum and in the adipose cells ofthe dermis and hy-

podermis,causing the skin to develop a yellowish tint that slowly

disappears once carotene intake is reduced.

Blood ﬂowing through the skin imparts a reddish hue,and,

when blood ﬂow increases (e.g.,during blushing, anger,and the in-

ﬂammatory response), the red color intensiﬁes. A decrease in

blood ﬂow such as occurs in shock can make the skin appear pale,

and a decrease in the blood oxygen content produces cyanosis(sı¯-

a˘-no¯⬘sis),a bluish skin color.

10. Which cells of the epidermis produce melanin? What

happensto the melanin once it is produced?

11. How do genetic factors, hormones, and exposure to light

determine the amountof melanin in the skin?

12. How do melanin, carotene, and blood affect skin color?

PREDICT

Explain the differencesin skin color between (a) the palms ofthe hands

and the lips, (b) the palmsof the hands of a person who does heavy

manuallabor and one who does not, (c) the anterior and posterior

surfacesof the forearm, and (d) the genitals and the solesof the feet.

AccessorySkin Structures

Objectives

■ Describe the types of hair and the structure of a hairand its

follicle. Discussthe stages of hair growth.

■ Describe the glands of the skin and their secretions.

■ Describe the parts of a nail, and explain how the nails are

produced.

Hair

The presence of hair is one of the characteristics common to all

mammals;if the hair is dense and covers most of the body surface,

it is called fur.In humans, hair is found everywhere on the skin ex-

cept the palms,soles, lips, nipples, parts of the external genitalia,

and the distal segments ofthe ﬁngers and toes.

Part2 Supportand Movement150

By the ﬁfth or sixth month offetal development, delicate un-

pigmented hair called lanugo(la˘-noo⬘go¯) develops and covers the

fetus. Near the time of birth, terminal hairs, which are long,

coarse,and pigmented, replace the lanugo of the scalp, eyelids, and

eyebrows.Vel lus (vel⬘u˘s) hairs,which are short, ﬁne, and usually

unpigmented, replace the lanugo on the rest of the body.At pu-

berty,terminal hair,especially in the pubic and axillar y regions,re-

places much ofthe vellus hair. The hair of the chest, legs, and arms

is approximately 90% terminal hair in males compared with ap-

proximately 35% in females.In males, terminal hairs replace the

vellus hairs ofthe face to form the beard. The beard, pubic, and ax-

illary hair are signs of sexual maturity.In addition, pubic and axil-

lary hair may function as wicks for dispersing odors produced by

secretions from specialized glands in the pubic and axillary re-

gions. It also has been suggested that pubic hair provides protec-

tion against abrasion during intercourse,and axillary hair reduces

friction when the armsmove.

HairStructure

A hair is divided into the shaftand root (ﬁgure 5.6a). The shaft pro-

trudes above the surface ofthe skin, and the root is located below the

surface.The base of the root is expanded to form the hair bulb (ﬁg-

ure 5.6b).Most of the root and the shaft of the hair are composed of

columns of dead keratinized epithelial cells arranged in three con-

centric layers:the medulla, the cortex, and the cuticle (ﬁgure 5.6c).

Themedulla (me-dool⬘a˘) is the central axis ofthe hair and consists

of two or three layers of cells containing soft keratin. The cortex

forms the bulk of the hair and consists of cells containing hard ker-

atin.The cuticle (ku¯⬘ti-kl) is a single layer of cells that forms the hair

surface.The cuticle cells contain hard keratin, and the edges of the

cuticle cells overlap like shingles on a roof.

Hard keratin contains more sulfur than does soft keratin.

When hair burns,the sulfur combines with hydrogen to form hy-

drogen sulﬁde,which produces the unpleasant odor of rotten eggs.

In some animals such as sheep, the cuticle edges of the hair are

raised and during textile manufacture catch each other and hold

together to form threads.

Melanocyte

Epithelial cell

Melanosomes

Nucleus

Golgi apparatus

Melanosomes are produced by the

Golgi apparatus of the melanocyte.

Melanosomes move into

melanocyte cell processes.

Epithelial cells phagocytize the tips

of the melanocyte cell processes.

These melanosomes are within

epithelial cells.

3 4

ProcessFigure 5.5

Melanin Transfer from Melanocyte to Keratinocytes

Melanocytesmake melanin, which is packaged into melanosomesand transferred to many keratinocytes.

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Chapter 5 Integumentary System 151

The hair follicle consists of a dermal root sheath and an

epithelial root sheath. The dermal root sheath is the portion of

the dermis that surrounds the epithelial root sheath.The epithelial

root sheath is divided into an external and an internal part (see ﬁg-

ure 5.6b).At the opening of the follicle, the external epithelial root

sheath has all the strata found in thin skin.Deeper in the hair folli-

cle, the number of cells decreases until at the hair bulb only the

stratum germinativum is present. This has important conse-

quences for the repair ofthe skin. If the epidermis and the superﬁ-

cial part of the dermis are damaged, the undamaged part of the

hair follicle that lies deep in the dermis can be a source ofnew ep-

ithelium.The internal epithelial root sheath has raised edges that

mesh closely with the raised edges of the hair cuticle and hold the

hair in place.When a hair is pulled out, the internal epithelial root

sheath usually comes out as well and is plainly visible as whitish tis-

sue around the root ofthe hair.

The hair bulb is an expanded knob at the base of the hair

root (see ﬁgure 5.6aand b). Inside the hair bulb is a mass of undif-

ferentiated epithelial cells,the matrix, which produces the hair and

the internal epithelial root sheath.The dermis of the skin projects

into the hair bulb as a papilla and contains blood vessels that pro-

vide nourishment to the cells ofthe matr ix.

HairGrowth

Hair is produced in cycles that involve a growth stageand a rest-

ing stage. During the growth stage, hair is formed by cells of the

matrix that differentiate, become keratinized,and die. The hair

grows longer as cells are added at the base ofthe hair root. Eventu-

ally hair growth stops;the hair follicle shortens and holds the hair

in place.A resting period follows after which a new cycle begins,

and a new hair replaces the old hair,which falls out of the hair

follicle. Thus loss of hair normally means that the hair is being

Hair shaft

(above skin

surface)

Hair root

(below skin

surface)

Hair bulb

(base of

hair root)

Artery

Vein

Fat

Medulla

Cortex

Cuticle

Arrector pili (smooth muscle)

Sebaceous

gland

Dermal root sheath

External epithelial

root sheath

Internal epithelial

root sheath

Matrix

Dermal papilla

Hair

follicle

Hair

Medulla

Cortex

Cuticle

Hair

Dermal root sheath

External epithelial

root sheath

Internal epithelial

root sheath

Melanocyte

Stratum basale

Basement membrane

Hair

follicle

Matrix

(growth zone)

Dermal

papilla

Hair

Medulla

Cortex

Cuticle

Hair follicle

Internal epithelial

root sheath

External epithelial

root sheath

Dermal root sheath

Figure 5.6

Hair Follicle

(a) The hair follicle containsthe hair and consistsof a dermal and epithelial root sheath. (b) Enlargement of the hair follicle wall and hair bulb. (c) Crosssection of a

hair within a hair follicle.

(a)

(b)

(c)

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Clinical Focus Burns

Burnsare classiﬁed according to the extent

of surface area involved and the depth of

the burn. For an adult, the surface area that

isburned can be conveniently estimated by

“the rule ofnines,” in which the body is di-

vided into areasthat are approximately 9%

or multiplesof 9% of the total body surface

(ﬁgure A). For younger patients, surface

area relationshipsare different. For exam-

ple, in an infant, the head and neckare 21%

of total surface area, whereasin an adult

theyare 9%. For burn victims younger than

age 15, a table speciﬁcallydeveloped for

them should be consulted.

On the basisof depth, burns are classi-

ﬁed as either partial-thickness or full-

thickness burns (ﬁgure B). Partial-

thicknessburns are divided into ﬁrst- and

second-degree burns. First-degree burns

involve onlythe epidermis and are red and

painful, and slight edema (swelling) may

occur. Theycan be caused by sunburn or

brief exposure to hot or cold objects, and

theyheal in a week or so without scarring.

Second-degree burns damage the

epidermis and the dermis. Minimal der-

mal damage causes redness, pain,

edema, and blisters. Healing takes ap-

proximately2 weeks, and no scarring re-

sults. If the burn goes deep into the

dermis, however, the wound appearsred,

tan, or white; maytake several months to

heal; and might scar. In all second-

degree burns the epidermis regenerates

from epithelialtissue in hair follicles and

sweat glands, aswell as from the edges

ofthe wound.

Full-thicknessburns are also called

third-degree burns. The epidermis and

dermis are completely destroyed, and

deeper tissue mayalso be involved. Third-

degree burns are often surrounded by

ﬁrst- and second-degree burns. Although

the areas that have first- and second-

degree burns are painful, the region of

third-degree burn is usually painless be-

cause ofdestruction of sensory receptors.

Third-degree burns appear white, tan,

Part2 Supportand Movement152

Head 9%

Upper limb 9%

Trunk 18%

(front or back)

Genitalia 1%

Lower limb 18%

Head 15%

Upper limb 9%

Trunk 16%

(front or back)

Genitalia 1%

Lower limb 17%

Figure A

The Rule ofNines

(a) In an adult, surface areascan be estimated using the rule ofnines: each major area of the body is 9%, or a multiple of 9%, of the total body surface area. (b) In

infantsand children the head represents a larger proportion of surface area. The rule ofnines is not as accurate for children, as can be seen in this 5-year-old child.

replaced.The length of each stage depends on the hair—eyelashes

grow for approximately 30 days and rest for 105 days,whereas scalp

hairs grow for a period of 3 years and rest for 1–2 years.At any

given time an estimated 90% ofthe scalp hairs are in the growing

stage,and loss of approximately 100 scalp hairs per day is normal.

The most common kind of permanent hair loss is “pattern

baldness.”Hair follicles are lost, and the remaining hair follicles

revert to producing vellus hair,which is very short, transparent,

and for practical purposes invisible.Although more common and

more pronounced in certain men, baldness can also occur in

(a) (b)

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Chapter 5 Integumentary System 153

Epidermis

Dermis

Hypodermis

Hair

follicle

Sweat

gland

Partial

thickness

Full

thickness

First

degree

Second

degree

Third

degree

Figure B

Burns

Partsof the skin damaged by burns of different degrees.

brown, black, or deep cherryred in color.

Skin can regenerate in a third-degree burn

only from the edges, and skin grafts are

often necessary.

Deep partial-thickness and full-

thickness burns take a long time to heal

and form scar tissue with disﬁguring and

debilitating wound contracture. Skin grafts

are performed to prevent these complica-

tions and to speed healing. In a splitskin

graft, the epidermisand part of the dermis

are removed from another partof the body

and are placed over the burn. Interstitial

ﬂuid from the burned area nourishes the

graft until it becomesvascularized. Mean-

while, the donor tissue producesnew epi-

dermis from epithelial tissue in the hair

folliclesand sweat glands such as occurs in

superﬁcialsecond-degree burns.

Other typesof grafts are possible, and

in casesin which a suitable donor site isnot

practical, artiﬁcial skin or grafts from hu-

man cadaversor from pigs are used. These

techniques are often unsatisfactory be-

cause the body’simmune system recognizes

the graftas a foreign substance and rejects

it. A solution to this problem is laboratory-

grown skin. A piece ofhealthy skin from the

burn victim is removed and placed into a

ﬂask with nutrients and hormones that

stimulate rapid growth. The skin thatis pro-

duced consistsonly of epidermis and does

notcontain glands or hair.

women.Genetic factors and the hormone testosterone are involved

in causing pattern baldness.

The average rate ofhair growth is approximately 0.3 mm per

day,although hairs g row at different rates even in the same ap-

proximate location.Cutting, shaving, or plucking hair does not al-

ter the growth rate or the character of the hair,but hair can feel

coarse and bristly shortly after shaving because the short hairs are

less ﬂexible.Maximum hair length is determined by the rate of hair

growth and the length of the growing phase. For example, scalp

hair can become very long,but eyelashes are short.

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HairColor

Melanin is produced by melanocytes within the hair bulb matrix

and passed to keratinocytes in the hair cortex and medulla.As with

the skin, varying amounts and types of melanin cause different

shades of hair color.Blonde hair has little black-brown melanin,

whereas jet black hair has the most. Intermediate amounts of

melanin account for different shades ofbrown. Red hair is caused

by varying amounts ofa red ty pe of melanin. Hair sometimes con-

tains both black-brown and red melanin.With age, the amount of

melanin in hair can decrease,causing the color of the hair to fade

or become white (i.e.,no melanin). Gray hair is usually a mixture

ofunfaded, faded, and white hairs. Hair color is controlled by sev-

eral genes, and dark hair color is not necessarily dominant over

light.

PREDICT

Marie Antoinette’shair supposedly turned white overnight after she

heard she would be sentto the guillotine. Explain why you believe or

disbelieve thisstory.

Muscles

Associated with each hair follicle are smooth muscle cells,the ar-

rector pili (a˘-rek⬘to¯r pı¯⬘lı¯),that extend from the dermal root

sheath of the hair follicle to the papillary layer of the dermis (see

ﬁgure 5.6a).Normally, the hair follicle and the hair inside it are at

an oblique angle to the surface of the skin.When the arrector pili

muscles contract, however,they pull the follicle into a position

more perpendicular to the surface of the skin,causing the hair to

“stand on end.”Movement of the hair follicles produces raised ar-

eas called “gooseﬂesh,”or “goose bumps.”

Contraction of the arrector pili muscles occurs in response

to cold or to frightening situations,and in animals with fur the re-

sponse increases the thickness ofthe fur. When the response results

from cold temperatures,it is beneﬁcial because the fur traps more

air and thus becomes a better insulator.In a frightening situation

the animal appears larger and more ferocious,which might deter

an attacker.It is unlikely that humans, with their sparse amount of

hair,derive any important beneﬁt from either response and proba-

bly retain this trait as an evolutionary holdover.

13. When and where are lanugo, vellus, and terminal hairs

found in the skin?

14. Deﬁne the root, shaft, and hair bulb of a hair. Describe the

three partsof a hair seen in cross section.

15. Describe the parts of a hair follicle. How is the epithelial

rootsheath important in the repair of the skin?

16. In what part of a hair does growth take place? What are the

stagesof hair growth?

17. Explain the location and action of arrector pili muscles.

Glands

The major glands of the skin are the sebaceous glands and the

sweat glands (ﬁgure 5.7).

SebaceousGlands

Sebaceous(se¯-ba¯⬘shu˘s)glands, located in the dermis, are simple

or compound alveolar glands that produce sebum (se¯⬘bu˘m), an

Part2 Supportand Movement154

oily,white substance rich in lipids.Because sebum is released by the

lysis and death of secretory cells,sebaceous glands are classiﬁed as

holocrine glands (see chapter 4). Most sebaceous glands are con-

nected by a duct to the upper part ofthe hair follicles from which

the sebum oils the hair and the skin surface.This prevents drying

and provides protection against some bacteria. A few sebaceous

glands located in the lips,in the eyelids (meibomian glands), and in

the genitalia are not associated with hairs but open directly onto

the skin surface.

SweatGl ands

Two types ofsweat, or sudoriferous (soo-do¯-rif⬘er-u˘s),glands ex-

ist,and at one time it was believed that one released its secretions

in a merocrine fashion and the other in an apocrine fashion (see

chapter 4).Accordingly, they were called merocrine and apocrine

sweat glands.It is now known that apocrine sweat glands also re-

lease some oftheir secretions in a merocrine fashion, and possibly

some in a holocrine fashion.Traditionally,the y are still referred to

as apocrine sweat glands.

Merocrine (mer⬘o¯-krin,mer⬘o¯-krı¯n, mer⬘o¯-kre¯ n), or ec-

crine (ek⬘rin), sweat glands are the most common type of sweat

gland. They are simple coiled tubular glands that open directly

onto the surface of the skin through sweat pores (see ﬁgure 5.7).

Merocrine sweat glands can be divided into two parts: the deep

coiled portion,which is located mostly in the dermis, and the duct,

which passes to the surface ofthe skin. The coiled part of the gland

produces an isotonic ﬂuid that is mostly water but also contains

some salts (mainly sodium chloride) and small amounts ofammo-

nia,urea, uric acid, and lactic acid. As this ﬂuid moves through the

duct, sodium chloride moves by active transport from the duct

Sweat pores

Sebaceous gland

Arrector pili

(smooth muscle)

Merocrine

sweat gland

Duct

Hair follicle

Hair bulb

Apocrine

sweat gland

Duct

Figure 5.7

Glandsof the Skin

Merocrine sweatglands open to the surface of the skin. Apocrine sweat

glandsand sebaceous glands open into hair follicles.

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back into the body,thereby conserving salts. The resulting hypos-

motic ﬂuid that leaves the duct is called sweat. When the body

temperature starts to rise above normal levels, the sweat glands

produce sweat, which evaporates and cools the body.Sweat also

can be released in the palms,soles, and axillae as a result of emo-

tional stress.

Detecting Lies

Emotionalsweating is used in lie detector (polygraph) tests because

sweatgland activity can increase when a person tells a lie. The sweat

produced, even in smallamounts, can be detected because the salt

solution conductselectricity and lowers the electric resistance ofthe skin.

Merocrine sweat glands are most numerous in the palms of

the hands and the soles of the feet but are absent from the margin

of the lips,the labia minora, and the tips of the penis and clitoris.

Only a few mammals such as humans and horses have merocrine

sweat glands in hairy skin. Dogs,on the other hand, keep cool by

water lost through panting instead ofsweating.

Apocrine (ap⬘o¯-krin) sweat glands are compound coiled tu-

bular glands that usually open into hair follicles superﬁcial to the

opening ofthe sebaceous glands (see ﬁgure 5.7). In other mammals,

these glands are widely distributed throughout the skin and help to

regulate temperature.In humans, apocrine sweat glands are found

in the axillae and genitalia (scrotum and labia majora) and around

the anus and do not help to regulate temperature.In humans, apo-

crine sweat glands become active at puberty as a result ofthe inﬂu-

ence ofsex hormones. Their secretions contain organic substances,

such as 3-methyl-2-hexenoic acid,that are essentially odorless when

ﬁrst released but that are quickly metabolized by bacteria to cause

what commonly is known as body odor.Many mammals use scent

as a means ofcommunication, and it has been suggested that the ac-

tivity ofapocr ine sweat glands may be a sign of sexual maturity.

OtherGlands

Other skin glands include the ceruminous glands and the

mammary glands. The ceruminous (se˘-roo⬘mi-nu˘s)glands are

modiﬁed merocrine sweat glands located in the ear canal (external

auditory meatus).Cerumen, or earwax, is the combined secretions

ofceruminous glands and sebaceous glands. Cerumen and hairs in

the ear canal protect the eardrum by preventing the entry of dirt

and small insects. An accumulation of cerumen, however,can

block the ear canal and make hearing more difﬁcult.

The mammary glands are modiﬁed apocrine sweat glands

located in the breasts.They function to produce milk. The struc-

ture and regulation ofmammary glands is discussed in chapter 29.

18. What secretion is produced by the sebaceous glands? What

isthe function of the secretion?

19. Which glands of the skin are responsible for cooling the

body? Which glandsare involved with the production of

bodyodor?

Nails

The distal ends of primate digits have nails, whereas most other

mammals have claws or hooves.Nails protect the ends ofthe digits,

aid in manipulation and grasping ofsmall objects, and are used for

scratching.

Anail consists of the proximal nail rootand the distal nail

body (ﬁgure 5.8a). The nail root is covered by skin,and the nail

body is the visible portion of the nail. The lateral and proximal

edges of the nail are covered by skin called the nail fold,and the

edges are held in place by the nail groove (ﬁgure 5.8b). The

Free edge

Nail body

Nail groove

Nail fold

Lunula

Eponychium

(cuticle)

Nail root

Bone

Nail fold

Nail body

Nail groove

Epidermis

Nail

matrix

Bone

Nail root

(under the skin)

Eponychium

Nail body

Nail bed

Free edge

Epidermis

Hyponychium

Figure 5.8

Nail

(a) Dorsalview. (b) Cross section. (c) Longitudinalsection.

(a)

(b)

(c)

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stratum corneum of the nail fold grows onto the nail body as the

eponychium(ep-o¯-nik⬘e¯-u˘m),or cuticle. Beneath the free edge of

the nail body is the hyponychium (hı¯⬘po¯-nik⬘e¯-u˘m), a thickened

region ofthe str atum corneum (ﬁgure 5.8c).

The nail root and the nail body attach to the nail bed, the

proximal portion ofwhich is the nail matrix. Only the st ratum ger-

minativum is present in the nail bed and nail matrix.The nail matrix

is thicker than the nail bed and produces most ofthe nail, although

the nail bed does contribute.The nail bed is visible through the clear

nail and appears pink because ofblood vessels in the dermis. A small

part of the nail matrix, the lunula (loo⬘noo-la˘), is seen through the

nail body as a whitish,crescent-shaped area at the base of the nail.

The lunula,seen best on the thumb, appears white because the blood

vessels cannot be seen through the thicker nail matrix.

The nail is stratum corneum. It contains a hard keratin

which makes the nail hard.The nail cells are produced in the nail

matrix and pushed distally over the nail bed.Nails grow at an aver-

age rate of0.5–1.2 mm per day, and ﬁngernails grow more rapidly

than toenails.Nails, like hair,grow from the base. Unlike hair, they

grow continuously throughout life and do not have a resting phase.

20. Name the parts of a nail. Which part produces most of the

nail? Whatis the lunula?

21. What makes a nail hard? Do nails have growth stages?

Summary of Integumentary

System Functions

Objective

■ Discuss the functions of the skin, hair, nails, and glands.

Protection

The integumentary system is the body’s fortress,defending it from

harm.It performs many protective functions.

1. The stratiﬁed squamous epithelium ofthe skin protects

underlying structures against abrasion.As the outer cells of

the stratum corneum are desquamated,they are replaced by

cells from the stratum basale.Calluses develop in areas

subject to heavy friction or pressure.

2. The skin prevents the entry ofmicroorganisms and other

foreign substances into the body.Secretions from skin glands

produce an environment unsuitable for some microorganisms.

The skin contains components ofthe immune system that act

against microorganisms (see chapter 22).

3. Melanin absorbs ultraviolet light and protects underlying

structures from its damaging effects.

4. Hair provides protection in several ways.The hair on the

head acts as a heat insulator and protects against ultraviolet

light and abrasion.The eyebrows keep sweat out of the eyes,

eyelashes protect the eyes from foreign objects,and hair in

the nose and ears prevents the entry ofdust and other

materials.Axillary and pubic hair are a sign of sexual

maturity and protect against abrasion.

5. Nails protect the ends ofthe digits from damage and can be

used in defense.

Part2 Supportand Movement156

6. The intact skin plays an important role in preventing water

loss because its lipids act as a barrier to the diffusion ofwater.

Administering MedicationsThrough the Skin

Some lipid-soluble substancesreadily passthrough the epidermis. Lipid-

soluble medicationscan be administered by applying them to the skin,

after which the medication slowlydiffuses through the skin into the blood.

For example, nicotine patchesare used to help reduce withdrawal

symptomsin those attempting to quit smoking.

Sensation

The body feels pain,heat, and cold because the integumentary sys-

tem has sensory receptors in all its layers.For example, the epider-

mis and dermal papillae are well supplied with touch receptors.

The dermis and deeper tissues contain pain,heat, cold, touch, and

pressure receptors.Hair follicles (but not the hair) are well inner-

vated,and movement of hair can be detected by sensory receptors

surrounding the base of hair follicles. Sensory receptors are dis-

cussed in more detail in chapter 14.

Temperature Regulation

Body temperature tends to increase as a result ofexercise, fever, or

an increase in environmental temperature.Homeostasis is main-

tained by the loss ofexcess heat. The blood vessels (arterioles) in the

dermis dilate and allow more blood to ﬂow through the skin,thus

transferring heat from deeper tissues to the skin (ﬁgure 5.9a). To

counteract environmental heat gain or to get rid ofexcess heat pro-

duced by the body,sweat is produced. The sweat spreads over the

surface ofthe skin, and as it evaporates, heat is lost from the body.

Ifbody temperature begins to drop below normal, heat can be

conserved by a decrease in the diameter ofdermal blood vessels, thus

reducing blood ﬂow to the skin (ﬁgure 5.9b).With less warm blood

ﬂowing through the skin,however,the skin temperature decreases. If

the skin temperature drops below approximately 15⬚C (59⬚F),blood

vessels dilate,which helps to prevent tissue damage from the cold.

Contraction of the arrector pili muscles causes hair to stand

on end,but with the sparse amount of hair covering the body, this

does not signiﬁcantly reduce heat loss in humans. Hair on the

head,however, is an effective insulator.General temperature regu-

lation is considered in chapter 25.

PREDICT

You mayhave noticed thaton very cold winter days, people’s ears and

nosesturn red. Can you explain why this happens?

Vitamin D Production

Vitamin Dfunctions as a hormone to stimulate uptake of calcium

and phosphate from the intestines,to promote their release from

bones,and to reduce calcium loss from the kidneys, resulting in in-

creased blood calcium and phosphate levels. Adequate levels of

these minerals are necessary for normal bone metabolism (see

chapter 6),and calcium is required for normal nerve and muscle

function (see chapter 9).

Vitamin D synthesis begins in skin exposed to ultraviolet

light,and humans can produce all the vitamin D they require by this

process ifenough ultraviolet light is available. Because humans live

indoors and wear clothing, however,their exposure to ultraviolet

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Chapter 5 Integumentary System 157

light may not be adequate for the manufacture of sufﬁcient vita-

minD. This is especially likely for people living in cold climates be-

cause they remain indoors or are covered by warm clothing when

outdoors.Fortunately,v itamin D can also be ingested and absorbed

in the intestine. Natural sources ofvitamin D are liver (especially

ﬁsh liver), egg yolks,and dairy products (e.g., butter, cheese, and

milk).In addition, the diet can be supplemented with vitamin D in

fortiﬁed milk or vitamin pills.

Vitamin D synthesis begins when the precursor molecule,

7-dehydrocholesterol (7-de¯-hı¯⬘dro¯-ko¯-les⬘ter-ol), is exposed to ul-

traviolet light and is converted into cholecalciferol (ko¯ ⬘le¯-kal-

sif⬘er-ol).Cholecalciferol is released into the blood and modiﬁed

by hydroxylation (hydroxide ions are added) in the liver and kid-

neys to form active vitamin D (calcitriol;kal-si-tr ı¯⬘ol).

Excretion

Excretion is the removal ofwaste products from the body. In addi-

tion to water and salts, sweat contains a small amount of waste

products,such as urea, uric acid, and ammonia. Compared to the

kidneys,however, the quantity of waste products eliminated in the

sweat is insigniﬁcant,even when large amounts of sweat are lost.

22. In what ways does the skin provide protection?

23. What kind of sensory receptors are found in the skin, and

whyare they important?

24. How does the skin assist in the regulation of body

temperature?

25. Name the locations where cholecalciferol is produced and

then modiﬁed into vitamin D. Whatare the functions of

vitamin D?

26. What substances are excreted in sweat? Is the skin an

importantsite of excretion?

Effects of Aging on the

Integumentary System

Objective

■ Describe the changes that occur in the integumentary

system with increasing age.

As the body ages,the skin is more easily damaged because the

epidermis thins and the amount ofcollagen in the dermis decreases.

Skin infections are more likely,and repair of the skin occurs more

slowly.A decrease in the number of elastic ﬁbers in the dermis and

loss offat from the hypodermis cause the skin to sag and wrinkle.

The skin becomes drier with age as sebaceous gland activity

decreases.A decrease in the activity of sweat glands and a decrease

in the blood supply to the dermis result in a poor ability to regulate

body temperature. Death from heat prostration can occur in el-

derly individuals who do not take proper precautions.

The number offunctioning melanocytes generally decreases,

but in some localized areas,especially on the hands and the face,

melanocytes increase in number to produce age spots.(Age spots

are different from freckles, which are caused by an increase in

melanin production and not an increase in melanocyte numbers.)

White or gray hairs also occur because of a decrease in or lack of

melanin production.

Skin that is exposed to sunlight appears to age more rapidly

than nonexposed skin.This effect is observed on areas of the body,

such as the face and hands,that receive sun exposure (ﬁgure 5.10).

The effects of chronic sun exposure on the skin,however, are dif-

ferent from the effects ofnormal aging. In skin exposed to sunlight,

normal elastic ﬁbers are replaced by an interwoven mat ofthick,

elasticlike material, the number of collagen ﬁbers decreases,and

the ability ofkeratinocy tes to divide is impaired.

Blood vessel dilates

(vasodilation)

Epidermis

Heat loss

across

epidermis

Increased heat loss

Blood vessel constricts

(vasoconstriction)

Heat conservation

Epidermis

Figure 5.9

HeatExchange in the Skin

(a) Blood vesselsin the dermis dilate (vasodilate), thus allowing more blood to ﬂow through the blood vesselsclose to the surface, where heat is lost from the

body. (b) Blood vesselsin the dermis constrict (vasoconstrict), thusreducing blood ﬂow and heat loss.

(a) (b)

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Clinical Focus ClinicalDisorders of the Integumentary System

The IntegumentarySystem as a

DiagnosticAid

The integumentary system can be used in

diagnosisbecause it is easily observed and

often reﬂects events occurring in other

partsof the body. For example, cyanosis(sı¯-

a˘-no¯⬘sis), a bluish color to the skin thatre-

sultsfrom decreased blood oxygen content,

is an indication of impaired circulatory or

respiratory function. When red blood cells

wear out, theyare broken down, and part of

their contentsis excreted by the liver as bile

pigments into the intestine. Jaundice

(jawn⬘dis), a yellowish skin color, occurs

when excess bile pigmentsaccumulate in

the blood. If a disease like viralhepatitis

damagesthe liver, bile pigments are not ex-

creted and accumulate in the blood.

Rashesand lesions in the skin can be

symptomaticof problems elsewhere in the

body. For example, scarlet fever results

from a bacterialinfection in the throat. The

bacteria release a toxin into the blood that

causesthe pink-red rash for which this dis-

ease wasnamed. In allergic reactions (see

chapter 22), a release ofhistamine into the

tissues produces swelling and reddening.

The development of a rash (hives) in the

skin can indicate an allergy to foods or

drugssuch as penicillin.

The condition ofthe skin, hair, and nails

isaffected by nutritional status. In vitamin A

deﬁciencythe skin produces excess keratin

and assumesa characteristic sandpaper tex-

ture, whereasin iron-deﬁciency anemia the

nailslose their normal contour and become

ﬂator concave (spoon-shaped).

Hair concentrates many substances

thatcan be detected by laboratory analysis,

and comparison ofa patient’s hair to “nor-

mal” hair can be useful in certain diag-

noses. For example, lead poisoning results

in high levelsof lead in the hair. The use of

hair analysis asa screening test to deter-

mine the generalhealth or nutritionalstatus

ofan individual is unreliable, however.

BacterialInfections

Staphylococcusaureus is commonly found

in pimples, boils, and carbuncles and

causesimpetigo (im-pe-t ı¯⬘go¯ ), a disease of

the skin that usually affectschildren. It is

characterized bysmall blisters containing

pusthat easily rupture and form a thick, yel-

lowish crust. Streptococcus pyogenes

causes erysipelas (er-i-sip⬘e˘-las), swollen

red patchesin the skin. Burns are often in-

fected byPseudomonas aeruginosa,which

produces a characteristic blue-green pus

caused bybacterial pigment.

Acne is a disorder of the hair follicles

and sebaceous glands that affectsalmost

everyone atsome time or another. Although

the exactcause of acne isunknown, four fac-

torsare believed to be involved: hormones,

sebum, abnormal keratinization within hair

follicles, and the bacterium Propionibac-

terium acnes. The lesions apparentlybegin

with a hyperproliferation of the hair follicle

epidermis, and many cells are desqua-

mated. These cellsare abnormally sticky and

adhere to one another to form a massof cells

mixed with sebum thatblocks the hair folli-

cle. During puberty, hormones, especially

testosterone, stimulate the sebaceous

glands to increase sebum production. Be-

cause both the adrenalgland and the testes

produce testosterone, the effectis seen in

both malesand females. An accumulation of

sebum behind the blockage produces a

whitehead, which maycontinue to develop

into a blackhead or a pimple. A blackhead re-

sults if the opening of the hair follicle is

pushed open bythe accumulating corniﬁed

cells and sebum. Although it is generally

agreed that dirt is not responsible for the

blackcolor of blackheads, the exactcause of

the blackcolor is disputed. Once the wall of

the follicle ruptures, P. ac nes and other mi-

croorganismsstimulate an inﬂammatory re-

sponse thatresults in the formation of a red

pimple ﬁlled with pus. Iftissue damage isex-

tensive, scarring occurs.

ViralInfections

Some of the well-known viralinfections of

the skin include chicken pox (varicella-

zoster), measles, German measles

(rubella), and cold sores(herpes simplex).

Warts, which are caused by a viral infection

of the epidermis, are generally harmless

and usuallydisappear without treatment.

FungalInfections

Ringworm is a fungal infection that affects

the keratinized portion ofthe skin, hair, and

nailsand produces patchy scaling and an in-

ﬂammatory response. The lesionsare often

circular with a raised edge, and in ancient

times they were thought to be caused by

worms. Severalspecies of fungus cause ring-

worm in humansand are usually described

bytheir location on the body; in the scalp the

condition isringworm, in the groin it is jock

itch, and in the feetit is athlete’s foot.

DecubitusUlcers

Decubitus(de¯-ku¯⬘bi-tu˘s)ulcers, also known

as bedsores or pressure sores, develop in

patientswho are immobile (e.g., bedridden

or conﬁned to a wheelchair). The weightof

the body, especiallyin areas over bony pro-

jections such asthe hipbones and heels,

compresses tissues and causes ischemia

(is-ke¯⬘me¯-a˘ ), or reduced circulation. The

consequence isdestruction, or necrosis (ne˘-

kro¯⬘sis), of the hypodermis and deeper tis-

sues, which is followed bynecrosis of the

skin. Once skin necrosisoccurs, microorgan-

ismsgain entry to produce an infected ulcer.

Bullae

Bullae(bul⬘e¯), or blisters, are ﬂuid-ﬁlled ar-

eas in the skin thatdevelop when tissues

are damaged, and the resultantinﬂamma-

tory response produces edema. Infections

or physicalinjuries can cause bullae or le-

sionsin different layers of the skin.

Psoriasis

Psoriasis (so¯-rı¯⬘a˘-sis) is characterized by a

thicker-than-normalstratum corneum that

sloughs to produce large, silveryscales. If

the scales are scraped away, bleeding oc-

cursfrom the blood vessels at the top of the

dermalpapillae. These changes result from

increased cell division in the stratum

basale, abnormal keratin production, and

elongation of the dermal papillae toward

the skin surface. Evidence suggeststhatthe

disease hasa genetic component and that

the immune system stimulates the in-

creased celldivisions. Psoriasisis a chronic

disease that can be controlled with drugs

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and phototherapy (ultraviolet light) butas

yethas no cure.

Eczema and Dermatitis

Eczema (ek⬘ze˘-ma˘, eg⬘ze˘-ma˘ , eg-ze¯ ⬘ma˘)

and dermatitis (der-ma˘-tı¯⬘tis) are inflam-

matoryconditions of the skin. Cause of the

inflammation can be allergy, infection,

poor circulation, or exposure to physical

factors, such as chemicals, heat, cold, or

sunlight.

Birthmarks

Birthmarks are congenital (present at

birth) disorders of the capillaries in the

dermisof the skin. Usually they are only of

concern for cosmetic reasons. A straw-

berrybirthmark is a mass of soft, elevated

tissue thatappears bright red to deep pur-

ple in color. In 70% ofpatients, strawberry

birthmarks disappear spontaneously by

age 7. Portwine stainsappear as ﬂat, dull

red or bluish patchesthat persist through-

outlife.

Vitiligo

Vitiligo (vit-i-lı¯⬘go¯ ) is the development of

patches of white skin because the

melanocytes in the affected area are de-

stroyed, apparently by an autoimmune re-

sponse (see chapter 22).

Moles

A mole is an elevation of the skin that is

variable in size and isoften pigmented and

hairy. Histologically, a mole isan aggrega-

tion, or “nest,” of melanocytes in the epi-

dermis or dermis. They are a normal

occurrence, and most people have 10–20

moles, which appear in childhood and en-

large untilpuberty.

Cancer

Skin cancer is the most common type of

cancer (ﬁgure C). Although chemicalsand

radiation (xrays) are known to induce can-

cer, the developmentof skin cancer is most

often associated with exposure to ultravio-

let(UV) radiation from the sun, and, conse-

quently, mostskin cancers develop on the

face or neck. The group of people most

likely to have skin cancer are fair-skinned

(i.e., theyhave less protection from the sun)

or are older than 50 (i.e., they have had

long exposure to the sun).

Basal cell carcinoma (kar-si-no¯⬘ma˘),

the mostfrequent skin cancer, beginsin the

stratum basale and extendsinto the dermis

to produce an open ulcer. Surgicalremoval

or radiation therapycures this type of can-

cer, and fortunatelylittle danger exists that

the cancer willspread, or metastasize (me˘-

tas⬘ta˘-sı¯z), to other areas of the body if

treated in time. Squamous cell carcinoma

develops from stratum spinosum ker-

atinocytes that continue to divide asthey

produce keratin. Typically, the resultis a

nodular, keratinized tumor conﬁned to the

epidermis, but it can invade the dermis,

metastasize, and cause death. Malignant

melanoma(mel⬘a˘-no¯ ⬘ma˘) is a less common

form of skin cancer that arises from

melanocytes, usuallyin a preexisting mole.

The melanoma can appear asa large, ﬂat,

spreading lesion or asa deeply pigmented

nodule. Metastasisis common, and, unless

diagnosed and treated early in develop-

ment, thiscancer is often fatal. Other types

ofskin cancer are possible (e.g., metastasis

from other partsof the body to the skin).

Limiting exposure to the sun and using

sunscreenscan reduce the likelihood of de-

veloping skin cancer. Some concern over

the use of sunscreens, however, has re-

centlyarisen because of the different types

ofUV radiation they can block. Exposure to

UVB can cause sunburn and isassociated

with the development of basal cell and

squamous cell carcinomas. The develop-

mentof malignant melanoma is associated

with exposure to UVA. Sunscreens that

blockprimarily UVB allow longer exposure

to the sun withoutsunburning but thereby

increase exposure to UVA and the possible

developmentof malignant melanoma. Sun-

screensthat effectively block UVB and UVA

are advisable.

Figure C

Cancer ofthe Skin

(a) Basalcell carcinoma.

(b) Squamouscell carcinoma.

Chapter 5 Integumentary System 159

(a) (b)

(c)

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Mr. Sis a 23-year-old man who had difﬁculty falling asleep at night.

He often stayed up late watching television or reading untilhe fell

asleep. Mr. Swas also a chain smoker. One night he took several

sleeping pills. Unfortunately, he fellasleep before putting out his cig-

arette, which started a ﬁre. Asa result, Mr. S was severelyburned and

received full-thicknessand par tial-thicknessburns (ﬁgure Da). He

wasrushed to the emergency room and was eventually transferred to

a burn unit.

For the ﬁrstday after his accident, his condition was criticalbe-

cause he went into shock. Administration oflarge volumes of intra-

venous ﬂuid stabilized hiscondition. As part of his treatment, Mr. S

wasalso given a high-protein, high-calorie diet.

A weeklater, dead tissue was removed from the most serious

burns(ﬁgure Db), and a skin graft was performed. Despite the use of

topicalantimicrobial drugs and sterile bandages, some of the burns

became infected. An additionalcomplication was the development of

a venousthrombosis in his leg.

Although the burns were painful and the treatment waspro-

longed, Mr. Smade a full recovery. He no longer smokes.

Background Information

When large areas of skin are severelyburned, systemic effects are

produced that can be life-threatening. One effectis on capillaries,

which are the small blood vesselsin which ﬂuid, gases, nutrients,

and waste productsare normally exchanged between the blood and

tissues. Within minutes of a major burn injury, capillariesbecome

more permeable atthe burn site and throughout the body. As a result,

ﬂuid and electrolytes (see chapter 2) are lostfrom the burn wound

and into tissue spaces. The lossof ﬂuid decreases blood volume,

which decreasesthe ability of the heart to pump blood. The resulting

decrease in blood delivery to tissues can cause tissue damage,

shock, and even death. Treatmentconsists of administering intra-

venous ﬂuid at a faster rate than itleaks out of the capillaries. Al-

though thiscan reverse the shock and prevent death, ﬂuid continues

to leakinto tissue spaces causing pronounced edema, a swelling of

the tissues.

Typically, after 24 hours, capillarypermeability returns to nor-

mal, and the amount of intravenous fluid administered can be

greatly decreased. How burns result in capillary permeability

changesis not well understood. It is clear that following a burn, im-

munologic and metabolic changes occur that affect not only

capillariesbut the rest of the body as well. For example, mediators of

inﬂammation (see chapter 4), which are released in response to the

tissue damage, contribute to changes in capillary permeability

throughoutthe body.

Substancesreleased from the burn may also play a role in caus-

ing cellsto function abnormally. Burn injuries result in an almost im-

mediate hypermetabolicstate that persists until wound closure. Also

contributing to the increased metabolism isa resetting of the temper-

ature control center in the brain to a higher temperature and an

Systems Pathology

Burns

Partial-thickness

burn

Full-thickness

burn

Figure D

Burn Victim

(a) Partialand full-thickness burns. (b) Patient in a burn unit.

Part2 Supportand Movement160

(a)

(b)

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increase in the hormonesreleased by the endocrine system. For ex-

ample, epinephrine and norepinephrine from the adrenal glandsin-

crease cellmetabolism. Compared with a normal body temperature of

approximately37⬚C (98.6⬚F ), a body temperature of38.5⬚C (101.3⬚F)

istypical in burn patients, despite the higher loss of water by evapora-

tion from the burn.

In severe burns, the increased metabolic rate can result in

weightloss as great as 30%–40% ofthe patient’s preburn weight. To

help compensate, caloricintake maydouble or even triple. In addition,

the need for protein, which isnecessary for tissue repair, is greater.

The skin normally maintainshomeostasis by preventing the

entry of microorganisms. Because burns damage and even com-

pletely destroy the skin, microorganisms can cause infections. For

thisreason, burn patients are maintained in an aseptic environment,

which attempts to prevent the entry of microorganisms into the

wound. Theyare also given antimicrobial drugs, which kill microor-

ganismsor suppress their growth. Debridement, (da¯-bre¯d-mon⬘), the

removalof dead tissue from the burn, helps to prevent infections by

cleaning the wound and removing tissue in which infectionscould

develop. Skin grafts, performed within a weekof the injury, also pre-

vent infections by closing the wound and preventing the entry of

microorganisms.

Despite these efforts, however, infections still are the major

cause ofdeath of burn victims. Depression of the immune system dur-

ing the ﬁrstor second week after the injury contributes to the high in-

fection rate. The thermally altered tissue isrecognized as a foreign

substance that stimulatesthe immune system. As a result, the im-

mune system isoverwhelmed as immune system cellsbecome less ef-

fective and production of the chemicals that normally provide

resistance to infectionsdecreases (see chapter 22). The greater the

magnitude ofthe burn, the greater the depression of the immune sys-

tem, and the greater the riskof infection.

Venousthrombosis, the development of a clot in a vein, is also

a complication ofburns. Blood normally forms a clot when exposed to

damaged tissue, such asat a burn site, but the clot can block blood

ﬂow, resulting in tissue destruction. In addition, the concentration of

chemicalsin the blood that cause clotting increases for two reasons:

lossof ﬂuid from the burn and the increased release of clotting factors

from the liver.

PREDICT

When Mr. Sis ﬁrst admitted to the burn unit, the nursescarefully

monitor hisurine output. Why does that make sense in lightof his

injuries?

System Interactions

Skeletal Red bone marrow replaces red blood cells destroyed in the burnt skin.

Muscular Loss of muscle mass resulting from the hypermetabolic state caused by the burn.

Nervous Pain is sensed in the partial-thickness burns. The temperature-regulatory center in the brain is set to a higher temperature,

which contributes to increased body temperature. Abnormal K

⫹

concentrations disturb normal nervous system activity:

elevated levels are caused by release of K

⫹

from damaged tissues; low levels can be caused by rapid loss of K

⫹

in fluid

from the burn.

Endocrine Increased secretion of epinephrine and norepinephrine from the adrenalgland in response to the injury contributes to

increased body temperature by increasing cell metabolism.

Cardiovascular Increased capillary permeability causes decreased blood volume, resulting in decreased blood delivery to tissues, edema, and

shock. The pumping effectiveness of the heart is impaired by electrolyte imbalance and substances released from the burn.

Increased blood clotting causes venousthrombosis. Preferential delivery of blood to the injury promotes healing.

Lymphatic and Immune Inflammation increases in response to tissue damage. Later, depression of the immune system can result in infection.

Respiratory Airway obstruction caused by edema. Increased respiration rate caused by increased metabolism and lactic acid buildup.

Digestive Decreased blood delivery as a result of the burn causes degeneration of the intestinal lining and liver. Bacteria from the

intestine can cause systemic infections. The liver releases blood-clotting factorsin response to the injury. Increased

nutrients necessary to support increased metabolism and for repair of the integumentary system are absorbed.

Urinary The kidneys compensate for the increased fluid loss caused by the burn by greatly reducing or even stopping urine production.

Decreased blood volume causes decreased blood flow to the kidneys, which reduces urine output but can cause kidney

tissue damage. Hemoglobin, released from red blood cells damaged in the burnt skin, can obstruct urine flow in the

kidneys.

Chapter 5 Integumentary System 161

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27. Compared to young skin, why is aged skin more likely to be

damaged, wrinkled, and dry?

28. Why is heat potentially dangerous to the elderly?

29. Explain age spots and white hair.

30. What effect does exposure to sunlight have on skin?

Part2 Supportand Movement162

Figure 5.10

Effectsof Sunlight on Skin

(a) A 91 year old Japanese monkwho has spent most of hislife indoors.

(b) A 62 year old Native American woman who hasspent most of her life

outdoors.

Treatmentof Skin Wrinkles

Retin-A (tretinoin; tret⬘i-no¯ -in) is a vitamin A derivative that is being used

to treatskin wrinkles. It appears to be effective in treating ﬁne wrinkles

on the face, such asthose caused by long-term exposure to the sun, but

isnot effective in treating deep lines. One ironic side effect of Retin-A

use isincreased sensitivity to the sun’s ultravioletrays. Doctors

prescribing thiscream caution their patients to always use a sunblock

when theyare going to be outdoors.

The integumentary system consists ofthe skin, hair, nails, and a variety of

glands.

Overview ofthe Integumentary System

(p. 144)

The integumentary system separates and protects us from the external en-

vironment.Other functions include sensation, temperature regulation, vi-

tamin D production,and excretion of small amounts of waste products.

Hypodermis

(p. 144)

1. Located beneath the dermis,the hypodermis is loose connective

tissue that contains collagen and elastin ﬁbers.

2. The hypodermis attaches the skin to underlying structures and is a

site offat storage.

Skin

(p. 145)

Dermis

1. The dermis is connective tissue divided into two layers.

2. The reticular layer is the main layer.It is dense irregular connective

tissue consisting mostly ofcollagen.

3. The papillary layer has projections called papillae and is loose

connective tissue that is well supplied with capillaries.

Epidermis

1. The epidermis is stratiﬁed squamous epithelium divided into ﬁve

strata.

2. The stratum basale consists of keratinocytes,which produce the cells

ofthe more superﬁcial strata.

3. The stratum spinosum consists of several layers of cells held

together by many desmosomes.The stratum basale and the stratum

spinosum are sometimes called the stratum germinativum.

4. The stratum granulosum consists of cells ﬁlled with granules of

keratohyalin.Cell death occurs in this stratum.

5. The stratum lucidum consists of a layer of dead transparent cells.

6. The stratum corneum consists of many layers of dead squamous

cells.The most superﬁcial cells are desquamated.

7. Keratinization is the transformation of the living cells of the stratum

basale into the dead squamous cells ofthe stratum corneum.

• Keratinized cells are ﬁlled with keratin and have a protein

envelope,both of which contribute to structural strength. The cells

are also held together by many desmosomes.

• Intercellular spaces are ﬁlled with lipids from the lamellae that

contribute to the impermeability ofthe epidermis to water.

8. Soft keratin is found in skin and the inside of hairs,whereas hard

keratin occurs in nails and the outside ofhairs. Hard keratin makes

cells more durable,and these cells do not desquamate.

SUMMARY

(a)

(b)

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Chapter 5 Integumentary System 163

Thickand Thin Skin

1. Thick skin has all ﬁve epithelial strata.The dermis under thick skin

produces ﬁngerprints and footprints.

2. Thin skin contains fewer cell layers per stratum,and the stratum

lucidum is usually absent.Hair is found only in thin skin.

Skin Color

1. Melanocytes produce melanin inside melanosomes and then

transfer the melanin to keratinocytes.The size and distribution of

melanosomes determine skin color.Melanin production is

determined genetically but can be inﬂuenced by hormones and

ultraviolet light (tanning).

2. Carotene,an ingested plant pigment, can cause the skin to appear

yellowish.

3. Increased blood ﬂow produces a red skin color,whereas a decreased

blood ﬂow causes a pale skin.Decreased oxygen content in the

blood results in a bluish color called cyanosis.

AccessorySkin Structures

(p. 150)

Hair

1. Lanugo (fetal hair) is replaced near the time of birth by terminal

hairs (scalp,eyelids, and eyebrows) and vellus hairs.At puberty

vellus hairs can be replaced with terminal hairs.

2. Hair is dead keratinized epithelial cells consisting ofa central axis of

cells with soft keratin,known as the medulla, which is surrounded

by a cortex ofcells with hard keratin. The cortex is covered by the

cuticle,a single layer of cells ﬁlled with hard keratin.

3. A hair has three parts:the shaft, the root, and the hair bulb.

4. The hair bulb produces the hair in cycles involving a growth stage

and a resting stage.

5. Hair color is determined by the amount and kind of melanin present.

6. Contraction of the arrector pili muscles,which are smooth muscles,

causes hair to “stand on end”and produces “gooseﬂesh.”

Glands

1. Sebaceous glands produce sebum,which oils the hair and the

surface ofthe skin.

2. Merocrine sweat glands produce sweat that cools the body.Apocrine

sweat glands produce an organic secretion that can be broken down

by bacteria to cause body odor.

3. Other skin glands include ceruminous glands,which help to make

cerumen (earwax),and the mammary glands, which produce milk.

Nails

1. The nail consists of a nail root and a nail body resting on the nail

bed.

2. Part of the nail root,the nail matrix, produces the nail body, which

is several layers ofcells containing hard keratin.

Summaryof Integumentary System Functions

(p. 156)

Protection

1. The skin provides protection against abrasion and ultraviolet light,

prevents the entry ofmicroorganisms, helps to regulate body

temperature,and prevents water loss.

2. Hair protects against abrasion and ultraviolet light and is a heat

insulator.

3. Nails protect the ends ofthe digits.

Sensation

The skin contains sensory receptors for pain,touch,hot, cold, and pressure

that allow proper response to the environment.

Temperature Regulation

1. Through dilation and constriction of blood vessels,the skin controls

heat loss from the body.

2. Sweat glands produce sweat which evaporates and lowers body

temperature.

Vitamin D Production

1. Skin exposed to ultraviolet light produces cholecalciferol,which is

modiﬁed in the liver and then in the kidneys to form active vitamin D.

2. Vitamin D increases blood calcium levels by promoting calcium

uptake from the intestine,release of calcium from bone, and

reduction ofcalcium loss from the kidneys.

Excretion

Skin glands remove small amounts ofwaste products (e.g., urea, uric acid,

and ammonia) but are not important in excretion.

Effectsof Aging on the Integumentary System

(p. 157)

1. As the body ages,blood ﬂow to the skin declines, the skin becomes

thinner,and elasticity is lost.

2. Sweat and sebaceous glands are less active,and the number of

melanocytes decreases.

1. The hypodermis

a. is the layer of skin where the hair is produced.

b. is the layer ofskin where nails are produced.

c. connects the dermis to the epidermis.

d. is dense irregular connective tissue.

e. contains approximately halfof the body’s stored fat.

For questions 2–5,match the layer of the dermis with the correct

description or function:

a. papillary layer

b. reticular layer

2. The layer of the dermis closest to the epidermis

3. The layer of the dermis responsible for most of the structural

strength ofthe skin

4. The layer of the dermis responsible for ﬁngerprints and footprints

5. The layer of the dermis responsible for cleavage lines and striae

6. A layer of skin (where mitosis occurs) that replaces cells lost from

the outer layer ofthe epidermis is the

a. stratum corneum.

b. stratum basale.

c. stratum lucidum.

d. reticular layer.

e. hypodermis.

7. If a splinter penetrates the skin of the palm of the hand to the second

epidermal layer from the surface,the last layer damaged is the

a. stratum granulosum.

b. stratum basale.

c. stratum corneum.

d. stratum lucidum.

e. stratum spinosum.

For questions 8–12,match the layer of the epidermis with the correct

description or function:

a. stratum basale

b. stratum corneum

c. stratum granulosum

d. stratum lucidum

e. stratum spinosum

REVIEW AND COMPREHENSION

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

Companies, 2004

8. Production of keratin ﬁbers;formation of lamellar bodies;limited

amount ofcell division

9. Desquamation occurs;25 or more layers of dead squamous cells

10. Production of cells;melanocy tes produce and contribute melanin;

hemidesmosomes present

11. Production of keratohyalin granules;lamellar bodies release lipids;

cells die

12. Dispersion of keratohyalin around keratin ﬁbers;layer appears

transparent;cells dead

13. In which of these areas of the body is thick skin found?

a. back of the hand

b. abdomen

c. over the shin

d. bridge ofthe nose

e. heel of the foot

14. The function of melanin in the skin is

a. lubrication of the skin.

b. prevention ofskin infections.

c. protection from ultraviolet light.

d. to reduce water loss.

e. to help regulate body temperature.

15. Concerning skin color,which of these statements is not correctly

matched?

a. skin appears yellow—carotene present

b. no skin pigmentation (albinism)—genetic disorder

c. skin tans—increased melanin production

d. skin appears blue (cyanosis)—oxygenated blood

e. African-Americans darker than Caucasians—more melanin in

African-American skin

16. After birth,the ty pe of hair on the scalp,eyelids, and eyebrows is

a. lanugo.

b. terminal hair.

c. vellus hair.

17. Hair

a. is produced by the dermal root sheath.

b. consists ofliving keratinized epithelial cells.

c. is colored by melanin.

d. contains mostly soft keratin.

e. grows from the tip.

18. Given these parts of a hair and hair follicle:

1. cortex

2. cuticle

3. dermal root sheath

4. epithelial root sheath

5. medulla

Arrange the structures in the correct order from the outside ofthe

hair follicle to the center ofthe hair.

a. 1,4,3,5,2

b. 2,1,5,3,4

c. 3,4,2,1,5

d. 4,3,1,2,5

e. 5,4,3,2,1

19. Concerning hair growth:

a. Hair falls out of the hair follicle at the end of the growth stage.

b. Most ofthe hair on the body grows continuously.

c. Cutting or plucking the hair increases its growth rate and

thickness.

d. Genetic factors and the hormone testosterone are involved in

“pattern baldness.”

e. Eyebrows have a longer growth stage and resting stage than scalp

hair.

20. Smooth muscles that produce “goose bumps”when they contract

and are attached to hair follicles are called

Part2 Supportand Movement164

a. external root sheaths.

b. arrector pili.

c. dermal papillae.

d. internal root sheaths.

e. hair bulbs.

For questions 21–23,match the type of gland with the correct

description or function.

a. apocrine sweat gland

b. merocrine sweat gland

c. sebaceous gland

21. Alveolar glands that produce a white,oily substance; usually open

into hair follicles

22. Coiled tubular glands that secrete a hyposmotic ﬂuid that cools the

body;most numerous in the palms of the hands and soles of the feet

23. Secretions from these coiled tubular glands are broken down by

bacteria to produce body odor;found in the axillae, genitalia, and

around the anus

24. The lunula of the nail appears white because

a. it lacks melanin.

b. blood vessels cannot be seen through the thick nail matrix.

c. the eponychium decreases blood ﬂow to the area.

d. the nail root is much thicker than the nail body.

e. the hyponychium is thicker than the eponychium.

25. The stratum corneum of the nail fold grows onto the nail body as

the

a. eponychium.

b. hyponychium.

c. lunula.

d. nail bed.

e. nail matrix.

26. Most of the nail is produced by the

a. eponychium.

b. hyponychium.

c. nail bed.

d. nail matrix.

e. dermis.

27. The skin aids in maintaining the calcium and phosphate levels of

the body at optimum levels by participating in the production of

a. vitamin A.

b. vitamin B.

c. vitamin D.

d. melanin.

e. keratin.

28. Which ofthese processes increase(s) heat loss from the body?

a. dilation of dermal arterioles

b. constriction ofdermal arterioles

c. increased sweating

d. both a and c

e. both b and c

29. In third-degree (full-thickness) burns,both the epidermis and

dermis ofthe skin are destroyed. Which of the following conditions

wouldnot occur as a result of a third-degree burn?

a. dehydration (increased water loss)

b. increased likelihood ofinfection

c. increased sweating

d. loss ofsensation in the burned area

e. poor temperature regulation in the burned area

30. Which ofthe follow ing factors increasesw ith age?

a. blood ﬂow to the skin

b. number and diameter ofelastic ﬁbers in the skin

c. number of melanocytes in some localized areas of the skin

d. melanin production in the hair

e. activity of sebaceous and sweat glands in the skin

Answers in Appendix F

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

II. Support and Movement 5. Integumentary System

Companies, 2004

Chapter 5 Integumentary System 165

1. A woman has stretch marks on her abdomen,yet she states that she

has never been pregnant.Is this possible?

2. The skin of infants is more easily penetrated and injured by

abrasion than that ofadults. Based on this fact, which stratum of the

epidermis is probably much thinner in infants than that in adults?

3. Melanocytes are found primarily in the stratum basale of the

epidermis.In reference to their function, why does this location

make sense?

4. Harry Fastfeet,a white man, jogs on a cold day. What color would

you expect his skin to be (a) just before starting to run,(b) during

the run,and (c) 5 minutes after the run?

5. Why are your eyelashes not a foot long? Your ﬁngernails?

6. Given what you know about the cause ofacne, propose some ways

to prevent or treat the disorder.

7. A patient has an ingrown toenail,a condition in which the nail

grows into the nail fold.Would cutting the nail away from the nail

fold permanently correct this condition? Why or why not?

Answers in Appendix G

CRITICAL THINKING

1. Because the permeability barrier is mainly composed of lipids

surrounding the epidermal cells,substances that are lipid-soluble

easily pass through,whereas water-soluble substances have

difﬁculty.

2. a. The lips are pinker or redder than the palms of the hand. Several

explanations for this are possible:more blood vessels in the lips,

increased blood ﬂow could occur in the lips,or the blood vessels

could be easier to see through the epidermis ofthe lips. The last

possibility explains most ofthe difference in color between the

lips and the palms.The epidermis of the lips is thinner and not

as heavily keratinized as that ofthe palms. In addition, the

papillae containing the blood vessels in the lips are “high”and

closer to the surface.

b. A person who does manual labor has a thicker stratum corneum

on the palms (and possibly calluses) than a person who does not

perform manual labor.The thicker epidermis masks the

underlying blood vessels,and the palms do not appear as pink.

In addition,carotene accumulating in the lipids of the stratum

corneum might impart a yellowish cast to the palms.

c. The posterior surface of the forearm appears darker because of

the tanning effect ofultraviolet light from the sun.

d. The genitals normally have more melanin and appear darker

than the soles ofthe feet.

3. The story is not true. Hair color results from the transfer ofmelanin

from melanocytes to keratinocytes in the hair matrix as the hair

grows.The hair itself is dead. To turn white,the hair must grow out

without the addition ofmelanin, a process that takes weeks.

4. On cold days,skin blood vessels of the ears and nose can dilate,

bringing warm blood to the ears and nose and thus preventing

tissue damage from the cold.The increased blood ﬂow makes the

ears and nose appear red.

5. Reducing water loss is one of the normal functions of the skin. Loss

ofskin, or damage to the skin, can greatly increase water loss. In

addition,burning large areas of the skin results in increased

capillary permeability and additional loss of ﬂuid from the burn and

into tissue spaces.The loss of ﬂuid reduces blood volume, which

results in reduced blood ﬂow to the kidneys.Consequently,urine

output by the kidneys decreases,which reduces ﬂuid loss and

thereby helps to compensate for the ﬂuid loss caused by the burn.

The reduced blood ﬂow to the kidneys can cause tissue damage,

however.To counteract this effect,during the ﬁrst 24 hours

following the injury,part of the treatment for burn victims is the

administration oflarge volumes of ﬂuid. But, how much ﬂuid

should be given? The amount ofﬂuid given should be sufﬁcient to

match that lost plus enough to prevent kidney damage and allow the

kidneys to function.Urine output is therefore monitored. If it is too

low,more ﬂuid is administered, and if it is too high, less ﬂuid is

given.An adult receiving intravenous ﬂuids should produce 30–50

mL ofurine/hour, and children should produce 1 mL/kg of body

weight/hour.

ANSWERS TO PREDICT QUESTIONS

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