Chapter 5:

The Integumentary System

The structures and functions of the

integumentary system.

Structure of the Integument

• 16% of body mass• Composed of:

1. Cutaneous Membrane: 1. Epidermis– Superficial epithelium2. Dermis – underlying CT with blood supply

2. Accessory Structures: originate in dermis1. Hair2. Nails3. Exocrine Glands

Parts of the Integumentary System

Figure 5–1

Functions of the Integument

• Protects underlying tissues from infection, exposure and dehydration

• Excretes salts, water, and organic waste• Maintains normal body temp:

- conserve and radiate heat• Synthesizes Vitamin D3 for calcium

metabolism• Stores Nutrients and Fat• Sensory detection:

- touch, pressure, pain, and temp.

Connections

• Circulatory system:– blood vessels in the dermis

• Nervous system:– sensory receptors for pain, touch, and

temperature

The main structures and functions

of the epidermis.

Epidermis

• Avascular stratified squamous epithelium

• Nutrients and oxygen diffuse from capillaries in the dermis

Cells of the Epidermis

• Keratinocytes:– contain large amounts of keratin– the most abundant cells in the epidermis

• Thin Skin: Hairy– Covers most of the body – Has 4 layers of keratinocytes

• Thick Skin: No Hair– Covers the palms of the hands and soles of

the feet– Has 5 layers of keratinocytes

Structures of the Epidermis

• The 5 strata of keratinocytes in thick skin

Figure 5–3

Layers of the Epidermis

• From basal lamina to free surface:– stratum germinativum– stratum spinosum– stratum granulosum– stratum lucidum– stratum corneum

• Transit from stratum basale to stratum corneum: – 15-30 days

• Duration at stratum corneum: – 7-14 days

• Complete turnover ever 25-45 days

1. Stratum Germinativum/Basale

• The “germinative layer”: Single Layer– has many germinative (stem) cells or basal cells– is attached to basal lamina by hemidesmosomes– forms a strong bond between epidermis and dermis– Cells:

• basal/germinative cells (stem cells), melanocytes (melanin), some Merkel cells in hairless skin (touch receptors)

Structure:• Epidermal ridges (e.g., fingerprints) • Dermal papillae (tiny mounds):

– increase the area of basal lamina– strengthen attachment between epidermis and

dermis

Layers of the Epidermis

2. Stratum Spinosum:– 8-10 layers keratinocytes attached by desmosomes– some cells can divide– some Langerhans cells present (immune response)

3. Stratum Granulosum:– 3-5 layers keratinocytes producing keratin fibers,

keratohyaline granules, and lamellated granules• Keratin = basic structural component of hair and nails• Keratohyaline = Promotes dehydration of the cells and

cross-linking of keratin fibers

– No cell division, nuclei and organelles being to disintegrate

Layers of the Epidermis

4. Stratum Lucidum: - thick skin only, flat packed keratin filled keratinocytes

5. Stratum Corneum:– 15-30 layers dead keratinocytes that have

been keratinized (cornified)• Soft keratin fibers glued in paralled arrays by

keratohyaline– Extracellular space filled with glycolipids from

lamellated granules• Cornified = water and chemical resistant

– not water proof since interstitial fluid can evaporate

Ridges and Ducts

Figure 5–4

The corrugated border between dermis and epidermis helps bond the epidermis and dermis - increased surface area for attachmentIn thick skin epidermal ridges show on the surface as fingerprints: Function – enhance gripping

Dandruff is caused by excessive shedding of cells from the outer layer of skin in the scalp. Thus dandruff is

composed of cells from which epidermal layer?

1. stratum germinativum2. stratum spinosum3. stratum corneum4. stratum granulosum

A splinter that penetrates to the third layer of the epidermis of the

palm is lodged in which layer?

1. stratum lucidum2. stratum germinativum3. stratum spinosum4. stratum granulosum

Some criminals sand the tips of their fingers so as not to leave recognizable

fingerprints. Would this practice permanently remove fingerprints? Why

or why not?1. Yes, because the dermal

papillae die if exposed.2. No, because the ridge patterns

regenerate.3. Yes, because the stratum

germinativum thickens hiding ridge patterns.

4. No, because different ridge patterns will appear with re-growth.

Characteristics of Skin

• Skin is water resistant but not water proof:– Insensible perspiration:

• Water from interstitial fluids evaporate• Water loss can not be seen or felt • water loss through skin: ~500ml (1 pint)/day

– More if damaged (e.g. burn)

– Sensible perspiration:• Aware of water loss• Produced by active sweat glands

Characteristics of Skin

– Callus: • Thickening of skin, due to friction

– Blister:• Separation of epidermal layers or

epidermis form dermis• space fills with interstitial fluid

Skin Color

• Pigment based: epidermal pigments and blood pigments contribute to the color

1. Epidermal Pigmentation2. Dermal Circulation

Skin Color

1. Epidermal Pigmentation A. Carotene: yellow-orange, from diet

- converted into Vitamin A- localized to epithelium- functions in normal maintenance of epithelia and

photoreceptors- excess accumulates in stratum

corneum B. Melanin: Brown, from melanocytes

- for UV protection

1. Epidermal Pigmentation

• Melanocytes: in stratum basale– Synthesize melanin from tyrosine

(amino acid)– Packaged in melanosomes– Melanosomes are transferred to

cytoplasm of keratinocytes– Cluster around top side of nucleus– Eventually digested by lysosomes

• Everyone has ~1000 melanocytes/mm2

– Pale People: small melansomes, present on in stratum basale and spinosum

– Dark People: larger, greater number of melansomes, retained up through stratum granulosum

1. Epidermal Pigmentation

• Freckles:– Overproduction of melanin form single

melanocytes

• UV exposure:– Some needed for Vitamin D3 production– Excess = damage (DNA mutation)

• Harm Fibroblasts impaired maintenance of the dermis resulting in altered CT structures

– Wrinkles• Chromosomal damage of Epidermal cells or

melanocytes cancer– Squamous cell carcinoma– Melanoma

Skin2. Dermal Circulation: hemoglobin pigment

- Oxygenated blood:

- red color, hemoglobin in RBCs, through skin=pink - Vasodilation skin looks more red

- Vasoconstriction skin looks more pale - Cyanosis:

- low oxygen, blood deep purple, skin appears blue/purple

- results form low temp., heart failure, asthma

Abnormal Skin Color• Jaundice:

– Liver fails to excrete bile– Bile accumulates in skin = yellow

• Addison’s Disease: – Pituitary secretes excess adrenocorticotropic

hormone, stimulates melanoctyes, excess melanin, bronzing

• Albinism: – Genetic mutation in melanin biosynthesis pathway– Lack pigmentation in skin, hair and eyes

• Vitiligo:– Autoimmune disease destruction of

melanocytes

Vitamin D3 Production

• Cells of stratum spinosum and basale:– UV energy + cholesterol = Vitamin D3

• Vitamin D3:– used by kidney to synthesize the hormone

calcitriol• Calcitriol:

– necessary to signal small intestine to absorb calcium

• No VitD no calcitriol no calcium

absorption weak bones

KEY CONCEPT

• The epidermis:– is a multilayered, flexible, self-

repairing barrier– prevents fluid loss– protects from UV radiation

– produces vitamin D3

– resists abrasion, chemicals, and pathogens

Why does exposure to sunlight or sunlamps darken skin?

1. UV stimulates melanocytes.2. Melanin darkens in sunlight.3. Stratum corneum cells appear

brown.4. Keratin appears brown when

heated.

Why does the skin of a fair-skinned person appear red

during exercise in hot weather?

1. Sunlight stimulates erythrocyte production in skin.

2. Blood is diverted to the superficial dermis to eliminate heat.

3. Sunlight bleaches fair skin, allowing blood to be seen.

4. Heat stimulates cutaneous blood vessels, causing leaks.

In some cultures, women must be covered completely, except for their eyes, when

they go outside. Explain why these women exhibit a high incidence of problems with

their bones.

1. UV light prevents calcium deposition in bones.

2. Melanin production is necessary for bone growth.

3. Cloth prevents oxygen from diffusing into skin and bones.

4. UV light is necessary to produce the hormone cholecalciferol (vitamin D3).

The structures and functions of the dermis.

The Dermis

• Is located between epidermis and subcutaneous layer

• Anchors epidermal accessory structures – hair follicles, sweat glands

• Contains:– All cells of CT proper, accessory organs of

integument, blood vessels, lymphatic vessels, nerves, and sensory receptors

• Has 2 components:– outer papillary layer – deep reticular layer

Dermis• Papillary layer:

– Thin (20%)– Consists:

• Areolar CT• Comprise dermal papillae• Capillaries, lymphatics, and sensory neurons

– Function: feed epidermis

• Reticular Layer:– Thick (80%)– Consists:

• Dense irregular CT• Elastic and Collagen fibers

– Function: provide strength and flexibility

Dermis• Collagen fibers from reticular layer

– blend into papillary and subcutaneous layers to attach integument to body

• Wrinkles = Dermis stretched beyond its elastic capacity– collagen fibers damaged

• Stretch marks = collagen and elastic fibers torn– Thickened tissue resulting from pregnancy, weight

gain, muscle gain• Collagen and Elastin fibers arranged in parallel

bundles:– aligned to resist the expected direction of force =

lines of cleavage• Cuts parallel to lines of cleavage will heal faster

and with less scar than those perpendicular

Lines of Cleavage

Figure 5–7

Dermis• Dermis highly vascularized:

– must “feed” itself and epidermis above

• Contusion: – bruise, trauma that ruptures blood

vessels but does not break skin, blood pools in dermis and must be removed by phagocytes (slow process)

Dermatitis

• An inflammation of the papillary layer• Caused by

– infection, radiation, mechanical irritation, or chemicals (e.g., poison ivy)

• Characterized by – itch or pain

• Characteristics– Strong, due to collagen fibers– Elastic, due to elastic fibers– Flexible

Skin Damage

• Sagging and wrinkles (reduced skin elasticity) are caused by:– dehydration– age– hormonal changes– UV exposure

Sensory Perception in Integument

• Skin highly innervated for sensory perception, mostly in dermis

1. Merkel Cells2. Free Nerve Endings3. Meissner’s Corpuscles4. Pacinian/Lamellated Corpuscles

Sensory Perception in Integument

1. Merkel cells: deep layers of epidermis - superficial touch

2. Free Nerve Endings: superficial dermis- pain and temperature

3. Meissner’s Corpuscles: superficial dermis

- light tough

4. Pacinian/Lamellated Corpuscles: deep dermis

- pressure and vibrations

Thick Skin

Thin Skin

Where are the capillaries and sensory neurons that supply

the epidermis located?

1. reticular layer of the dermis

2. epidermis3. papillary layer of the

dermis4. hypodermic layer

What accounts for the ability of the dermis to undergo repeated

stretching?

1. elastic fibers and skin turgor resilience

2. reticular fibers and fluids3. adipocytes and elastic

fibers4. sebaceous gland secretions

The structures and functions of the subcutaneous layer.

The Hypodermis

• The subcutaneous layer or hypodermis: – lies below the integument– Not part of cutaneous membrane– Stabilizes position of skin while

permitting independent movement of skin and muscles

Subcutaneous Layer (aka Hypodermis)

• Areolar and adipose CT• Tightly interwoven with reticular layer

of dermis• Children: even layer of adipose• Puberty: Adipose shifts

– Male: neck, arms, abdomen, lower back– Female: breast, buttocks, hips, thighs

• No vital organs: safe for “SubQ” injection, vascular for quick absorption

KEY CONCEPT

• The dermis: – provides mechanical strength,

flexibility and protection – is highly vascularized– contains many types of sensory

receptors

Integumentary Accessory Structures

1. Hair and hair follicles2. Sebaceous glands3. Sweat glands4. Nails• Accessory Structures:

– are derived from embryonic epidermis – are located in dermis– project through the skin surface

Hair

• Human body: – ~2.5 million hairs, 75% on body

• Everywhere except: – palms, soles, lips, and certain genitalia

• Hair itself is dead, but is derived from live epidermal tissue

• Hair and Hair Follicle Structure

Hair growth, texture, and color.

Functions of Hair

• Function:– Protects and insulates– Guards openings against particles and insects– Is sensitive to very light touch

• Structure of Hair Follicle:– Hair Follicle– Glassy membrane– Hair bulb– Hair papilla– Hair Matrix

• Structure of Hair:– Hair root– Hair shaft

The Hair Follicle

• Hair is produced in organs called hair follicles

• Tube of stratified squamous epithelium anchored in dermis

• Surrounds, supports, and produces hair

• Two layers:– Internal Root Sheath:

• contacts hair

– External Root Sheath:• contacts glassy membrane

Hair Follicle Structure• Glassy membrane

– Thick basal lamina between epithelial follicle and connective tissue dermis

• Hair bulb consist of epithelial cells– Expanded base of follicle that

surrounds papilla and matrix– Responsible for producing hair by

forming the hair matrix layer• Hair Matrix

– Dividing epithelial/basal cells and melanocytes above papilla that form new hair

– Cells gradually push toward the surface

• Hair papilla– CT at base of bulb, contains

capillaries and nerves– Supports matrix

Hair Structure

• Hair Root: – Embedded in dermis– Not yet fully formed– Contains live cells

• Hair Shaft:– Pokes through epidermis– Fully organized dead hair– Three layers1. Cuticle: outermost, overlapping dead

keratinized cells form shiny surface2. Cortex: middle layer, dead cells contain hard

keratin to provide stiffness3. Medulla: core, dead cells contain soft keratin

and air to provide flexible

Hair Structure• Shape of the Shaft determines feel:

– Flattened shaft = kinky hair– Oval shaft = silky and wavy hair– Round shaft = straight and often stiff hair

• Two types of Hair produced:1. Vellus Hairs = “peach fuzz”

- Lacks medulla- Covers body, at puberty hormones can trigger

switch to terminal hairs- Vellus hairs present at the armpits, pubic area,

and limbs switch to terminal hairs in response to circulating sex hormones

2. Terminal Hairs = head, eyebrows and eyelashes- Thick, coarse, pigmented

Hair Color

• red: iron added• Range yellow to black due to

melanin from melanocytes in hair matrix– Melanin stored in cortex and medulla

With age, melanin declines, air pockets in medulla increase = gray or white hair

Hair Growth• Hair in the Scalp:

– Grows for 2-5 yrs, at a rate of 0.33 mm per day• During hair growth:

– Cells of the hair root absorb nutrients and incorporate them into the hair structure History of Exposure• Result clipping or collecting hair for analysis is

helpful in diagnosing several disorders (ex. Heavy Metals, nucleus = DNA)

– The root is firmly attached to the matrix of the follicle

• At the end of growth:– The follicle becomes inactive termed club hair

• Follicle gets smaller• Connections between the hair matrix and the club hair

root breaks down. • Another cycle begins:

– Follicle produces a new hair– The old club hair is pushed to the surface and shed

Hair Growth~0.33mm/day, not continuous: cycle of growth and rest1. Active phase:

- new hair added to hair root by dividing cells of hair matrix (weeks – years)

2. Regressive phase: - cells of hair matrix stop dividing- hair root and hair papilla separate loose hair = club hair

3. Resting phase: - cells of hair matrix and hair follicle remain inactive (1-3 months)

New Active Phase Begins

Hair length differences = difference in time spent in active phase:eyebrows = few monthshead – many years

• Shedding of the hair occurs only after the next growth cycle begins and a new hair shaft begins to emerge.

• On average 50 - 100 hairs are shed every day. • The percentage of follicles in the resting phase will

vary at any time depending on the body area. • Factors that can affect the hair growth cycle and

cause temporary or permanent hair loss (alopecia) including:– medication, radiation, chemotherapy, exposure

to chemicals, hormonal and nutritional factors, thyroid disease, generalized or local skin disease, stress, and high fevers.

Hair Growth• Alopecia:

– Shift from terminal hair to vellus hair, thinning/balding, some degree expected with age

• Male Pattern Baldness:– Genetic alopecia, early age onset– Caused by a shift from terminal to vellus hair

production due to a change in the level of sex hormones circulating in the blood

– Treatment: • Aimed at converting vellus hairs to terminal hairs

• Hair Removal:– Difficult to achieve permanent result– Any remaining matrix cells can regenerate all hair

follicle structures

Hair Function

• Head: – UV protection– Cushion from trauma– Insulation

• Nostrils, Ear canals, Eyelashes:– Prevent entry of foreign material

• Body Hair: – sensory detection

Hair Function: Sensory Detection

• Root hair plexus:– Sensory nerves at base of

hair follicle that detect slight movement of hair

• Arrector pili muscle:– Attached to every hair

follicle– Contract to stand hair

perpendicular to skin surface• Goose bumps

– Smooth muscle: involuntary

What happens when the arrector pili muscle contracts?

1. Sebum is released.2. Goose bumps are evident.3. Sweat is produced.4. Blood flow is increased.

Once a burn on the forearm that destroys the epidermis, and

extensive areas of the deep dermis heals, will hair grow again in the

affected area?

1. Yes.2. No.3. Only in areas where the deep

dermis was destroyed.4. Only in areas where the

epidermis and deep dermis were not destroyed.

The skin glands and secretions.

Exocrine Glands

• Sebaceous glands (oil glands):– holocrine glands (which destroys gland cells)– secrete sebum

• Sudoriferous Glands/Sweat Glands A. Merocrine/Eccrine sudoriferous glands B. Apocrine sudoriferous/sweat gland Sweat glands:

• merocrine glands• watery secretions

Integumentary Glands• All are exocrine glands

– Secrete product onto skin surface via a duct

1. Sebaceous glands- Holocrine secretion- Secrete sebum into hair follicle- Sebum = lipids + cholesterol + proteins +

electrolytes- Function:

- Lubricate and protect keratin- Prevent evaporation- Inhibit bacterial growth

Sebaceous glands active in fetus, then off until puberty, and then back on for the whole adult life

Acne = Inflammation of a sebaceous gland,* Usually due to bacterial infection

Integumentary Glands

2. Sudoriferous Glands/Sweat Glands A. Merocrine/Eccrine sudoriferous glands

- 2 to 5 million all over body- produce sensible perspiration: - 99% water - electrolytes + organic nutrients

+ antibodies + antimicrobial agents + organic waters

- merocrine secretion - secretion via exocytosis of vesicles- small coiled tubular glands- located in superficial dermis- open directly on surface of skin- secrete in response to high temp. or stress

Functions of Sensible Perspiration

1. Evaporation cooling of surface of skin to reduce body temp.

2. Excrete waste electrolytes and drugs3. Protection:

- Prevent adherence of microbes: antibodies

- Physically wash off microbes- Antimicrobial agents of kill microbes

- Dermiciden (antibiotic)

Integumentary Glands2. Sudoriferous Glands/Sweat Glands

B. Apocrine sudoriferous/sweat gland- merocrine secretion- armpits, nipples, groin- secrete into hair follicle- secretion is stick and cloudy:

- sensible perspiration + protein + lipids- microbes eat it wastes = body odor- glands deep in dermis- Surrounded by myoepithelial cells: myo = muscle

- contraction of cells in response to sympathetic nervous system

stimulation causes discharge of secretion- Active only after puberty

Special Apocrine Sweat Glands:1. Mammary Glands: - Located in female breast & Secrete milk during lactation2. Ceruminous Glands:

- Located in external ear canal & Secrete cerumen (earwax)

Integumentary Gland Control

• Merocrine sudoriferous glands:– can be turned on and off in localized regions

in response to temperature or emotions

• Sebaceous and apocrine sudoriferous glands:– Autonomic nervous system controls the

activation and deactivation of these glands therefore they affect all the glands

– are either all on (body wide) or all off– no local control

What are the functions of sebaceous secretions?

1. inhibits the growth of bacteria

2. lubricates and conditions the surrounding skin

3. lubricates and protects the keratin of the hair shaft

4. all of the above

Deodorants are used to mask the effects of secretions from which

type of skin gland?

1. ceruminous glands2. apocrine sweat glands3. merocrine sweat glands4. mammary glands

Which type of skin glands are most affected by the hormonal

changes that occur during puberty?

1. ceruminous glands2. sebaceous glands3. apocrine sweat glands4. merocrine sweat glands

The structure of nails.

Nails• Scale like projections on

dorsal surface of distal digits• Function:

– protect tips from mechanical stress, assist in gripping

• Consists of dead cells containing hard keratin

• New nail formed at nail root• Cuticle = stratum corneum• Nail growth is continuous

How injured skin responds and repair

itself.

Injury and Repair

• Integument can function independent of nervous and endocrine systems to maintain own homeostasis

• Mesenchymal cells of dermis can regenerate connective tissue

• Germinative cells (basal cells) of epidermis can regenerate tissue

Repair of Localized Injuries to the Skin: Step 1

• Bleeding occurs• Mast cells

trigger inflammatory response

Figure 5–13 (Step 1)

Repair of Localized Injuries to the Skin: Step 2

• A scab stabilizes and protects the area

Figure 5–13 (Step 2)

The Inflammatory Response

• Germinative cells migrate around the wound

• Macrophages clean the area• Fibroblasts and endothelial cells

move in, producing granulation tissue

Repair of Localized Injuries to the Skin: Step 3

• Fibroblasts produce scar tissue

• Inflammation decreases, clot disintegrates

Figure 5–13 (Step 3)

Repair of Localized Injuries to the Skin: Step 4

• Fibroblasts strengthen scar tissue

• A raised keloid forms

Figure 5–13 (Step 4)

Injury and Repair• Repair may end up like original tissue or

keloid– Keloid = thick area of scar tissue covered by

smooth epidermis

• Burns:– First degree burn: heals on own

• Damage to surface of epidermis– Second degree burn: heals on own

• Damage to epidermis and superficial dermis– Third degree burn: Requires skin grafts or “living bandages”

• Damage to whole cutaneous layer (epidermis, dermis, accessory structures), granulation tissue cannot form thus no healing

Burns

• If burn > 20% of body can kill

– It affects:1. Fluid and electrolyte

balance2. Thermoregulation3. Protection from

pathogens

What do you call the combination of fibrin clots, fibroblasts, and the extensive network of capillaries in

healing tissue?

1. granulation tissue2. scar3. scab4. callus

Why can skin regenerate effectively, even after considerable damage?

1. Stratum germinativum persists deep within the body.

2. Stem cells persist in all components of the skin.

3. Hypodermis will transform into epidermis and dermis.

4. Surrounding skin spreads and fills in damaged area.

The effects of aging on the skin.

Age Related Changes1. Stem cell activity declines:

- Skin thin, repair is difficult2. Langerhans cells decrease:

- Reduced immune response3. Vitamin D3 production declines:

- Calcium absorption declines brittle bones4. Glandular activity declines:

- skin dry, body can overheat5. Bloody supply to dermis declines:

- tend to feel cold6. Hair follicles die or produce thinner hair:

- terminal vellus7. Dermis thins and becomes less elastic wrinkles8. Sex characteristics fade:

- Fat deposits spread out, hair patterns change

Older individuals do not tolerate the summer heat as well as they did when they were young, and they are more prone to heat-related illness. What

accounts for these changes?

1. Blood supply to the dermis is reduced.

2. Glandular activity declines.3. Melanocyte activity declines.4. All of the above.

The integumentary system

work with other systems.

Importance of the Integumentary System

• Protects and interacts with all organ systems

• Changes in skin appearance are used to diagnose disorders in other systems

Interactions with the Integumentary System

Figure 5–15

SUMMARY

• Division of:– integument into epidermis and dermis– epidermis into thin skin and thick skin

• Layers of the epidermis:– stratum germinosum– stratum spinosum– stratum lucidum– stratum corneum

• Roles of epidermal ridges and dermal papillae

• Functions of specialized cells:– Langerhans cells & Merkel cells

SUMMARY

• Skin pigments:– Carotene & Melanin

• Metabolic functions of epidermis:– vitamin D3 &epidermal growth factor

• Divisions of the dermis:– papillary layer– reticular layer

• Mobility of the dermis:– stretch marks & lines of cleavage

• Blood supply of the dermis:– cutaneous plexus– papillary plexus

SUMMARY

• Role of the subcutaneous layer• Structure of hair and hair follicles• Glands of the skin:

– sebaceous– sweat– Ceruminous

• Structure of nails• Processes of inflammation and

regeneration• Effects of aging on the integument