Chapter 5

Principles of Human Anatomy and Physiology, 11e 1

Chapter 5

The Integumentary System

Lecture Outline


INTRODUCTION

• The skin and its accessory structures make up the integumentary system.

• The integumentary system functions to guard the body’s physical and biochemical integrity, maintain a constant body temperature, and provide sensory information about the surrounding environment.


Chapter 5The Integumentary System

• Skin and its accessory structures– structure– function– growth and repair– development– aging– disorders


General Anatomy

• A large organ composed of all 4 tissue types

• 22 square feet • 1-2 mm thick• Weight 10 lbs.


STRUCTURE OF THE SKIN (Figure 5.1)

• The superficial portion of the skin is the epidermis and is composed of epithelial tissue.

• The deeper layer of the skin is the dermis and is primarily composed of connective tissue.

• Deep to the dermis is the subcutaneous layer or hypodermis. (not a part of the skin)– It consists of areolar and adipose

tissue.– fat storage, an area for blood

vessel passage, and an area of pressure-sensing nerve endings.


Overview of Epidermis

• Stratified squamous epithelium– avascular (contains no blood vessels)– 4 types of cells– 5 distinct strata (layers) of cells


Four Principle Cells of the Epidermis – Figure 5.2

• keratinocytes (Figure 5.2a)

– produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes, and chemicals, and lamellar granules, which release a waterproof sealant

• melanocytes (Figure 5.2b)

– produce the pigment melanin which contributes to skin color and absorbs damaging ultraviolet (UV) light

• Langerhans cells (Figure 5.2c)

– derived from bone marrow

– participate in immune response

• Merkel cells (Figure 5.2d)

– contact a sensory structure called a tactile (Merkel) disc and function in the sensation of touch


Layers of the Epidermis

• There are four or five layers of the epidermis, depending upon the degree of friction and mechanical pressure applied to the skin.

• From deepest to most superficial the layers of the epidermis are (Figures 5.3 a and b).– stratum basale (stratum germinativum)– stratum spinosum– stratum granulosum– stratum lucidum (only in palms and soles)– stratum corneum


Layers (Strata) of the Epidermis• Stratum corneum• Stratum lucidum• Stratum granulosum• Stratum spinosum• Stratum basale


Stratum Basale (stratum germinativum)

• Deepest single layer of epidermis – merkel cells, melanocytes,

keratinocytes & stem cells that divide repeatedly

– keratinocytes have a cytoskeleton of tonofilaments

– Cells attached to each other & to basement membrane by desmosomes & hemi-desmosomes

• When the germinal portion of the epidermis is destroyed, new skin cannot regenerate with a skin graft.


Stratum Spinosum (Figure 5.3b)

• provides strength and flexibility to the skin – 8 to 10 cell layers are held

together by desmosomes.– During slide preparation,

cells shrink and appear spiny (where attached to other cells by desmosomes.)

• Melanin is taken in by keratinocytes (by phagocytosis) from nearby melanocytes.


Stratum Granulosum

• transition between the deeper, metabolically active strata and the dead cells of the more superficial strata

• 3-5 layers of flat dying cells that show nuclear degeneration– example of apoptosis

• Contain lamellar granules that release lipid that repels water

• Contain dark-staining keratohyalin granules– keratohyalin converts

tonofilaments into keratin


Stratum Lucidum

• present only in the fingers tips, palms of the hands, and soles of the feet.

• Three to five layers of clear, flat, dead cells

• Contains precursor of keratin


Stratum Corneum

• 25 to 30 layers of flat dead cells filled with keratin and surrounded by lipids– continuously shed

• Barrier to light, heat, water, chemicals & bacteria

• Lamellar granules in this layer make it water-repellent.

• Constant exposure to friction will cause this layer to increase in depth with the formation of a callus, an abnormal thickening of the epidermis.


Keratinization and Growth of the Epidermis

• Stem cells divide to produce keratinocytes• As keratinocytes are pushed up towards the surface, they fill

with keratin– Keratinization is replacement of cell contents with the

protein keratin; occurs as cells move to the skin surface over 2-4 weeks.

• Epidermal growth factor (EGF) and other hormone-like proteins play a role in epidermal growth.

• Table 5.1 presents a summary of the features of the epidermal strata.


Clinical Application

• Psoriasis is a chronic skin disorder characterized by a more rapid division and movement of keratinocytes through the epidermal strata .– cells shed in 7 to 10 days as flaky silvery scales– abnormal keratin produced

• Skin Grafts– New skin can not regenerate if stratum basale and its stem cells are

destroyed– autograft: covering of wound with piece of healthy skin from self– isograft is from twin– autologous skin

• transplantation of patient’s skin after it has grown in culture


Dermis (Figure 5.1)• Connective tissue layer composed of collagen & elastic

fibers, fibroblasts, macrophages & fat cells• Contains hair follicles, glands, nerves & blood vessels• Two major regions of dermis

– papillary region– reticular region


Dermis - Papillary Region

• Top 20% of dermis• areolar connective tissue containing fine elastic fibers, corpuscles of

touch (Meissner’s corpuscles), adipose cells, hair follicles, sebaceous glands, sudoriferous glands – The collagen and elastic fibers provide strength, extensibility (ability

to stretch), and elasticity (ability to return to original shape after stretching) to skin.

• Finger like projections are called dermal papillae– anchors epidermis to dermis– contains capillaries that feed epidermis– contains Meissner’s corpuscles (touch) & free nerve endings for

sensations of heat, cold, pain, tickle, and itch


Dermis - Reticular Region

• Dense irregular connective tissue• Contains interlacing collagen and elastic fibers• Packed with oil glands, sweat gland ducts, fat & hair follicles• Provides strength, extensibility & elasticity to skin

– stretch marks are dermal tears from extreme stretching• Epidermal ridges form in fetus as epidermis conforms to

dermal papillae– fingerprints are left by sweat glands open on ridges– increase grip of hand


Dermis -- Structure

• Epidermal ridges increase friction for better grasping ability and provide the basis for fingerprints and footprints. The ridges typically reflect contours of the underlying dermis.

• Lines of cleavage in the skin indicate the predominant direction of the underlying collagen fibers. Knowledge of these lines is especially important to plastic surgeons.

• Table 5.2 presents a comparison of the structural features of the papillary and reticular regions of the dermis.


Tattoos

• Tattooing is a permanent coloration of the skin in which a foreign pigment is injected into the dermis.


Basis of Skin Color

• The color of skin and mucous membranes can provide clues for diagnosing certain problems, such as – Jaundice

• yellowish color to skin and whites of eyes• buildup of yellow bilirubin in blood from liver disease

– Cyanosis• bluish color to nail beds and skin• hemoglobin depleted of oxygen looks purple-blue

– Erythema• redness of skin due to enlargement of capillaries in

dermis• during inflammation, infection, allergy or burns


Skin Color Pigments• Melanin produced in epidermis by melanocytes

– melanocytes convert tyrosine to melanin• UV in sunlight increases melanin production

– same number of melanocytes in everyone, but differing amounts of pigment produced

– results vary from yellow to tan to black color• Clinical observations

– freckles or liver spots = melanocytes in a patch– albinism = inherited lack of tyrosinase; no pigment– vitiligo = autoimmune loss of melanocytes in areas of the skin

produces white patches

• The wide variety of colors in skin is due to three pigments - melanin, carotene, and hemoglobin (in blood in capillaries) - in the dermis.


Skin Color Pigments

• Carotene in dermis– yellow-orange pigment (precursor of vitamin A)– found in stratum corneum & dermis

• Hemoglobin– red, oxygen-carrying pigment in blood cells– if other pigments are not present, epidermis is

translucent so pinkness will be evident


Accessory Structures of Skin

• develop from the embryonic epidermis

• Cells sink inward during development to form:– hair– oil glands– sweat glands– nails


HAIR

• Hairs, or pili, are present on most skin surfaces except the palms, palmar surfaces of the digits, soles, and plantar surfaces of the digits.

• Hair consists of – a shaft above the surface (Figure 5.4a)– a root that penetrates the dermis and

subcutaneous layer (Figure 5.4c,d)– the cuticle (Figure 5.4b), and – a hair follicle (Figure 5.4c,d).

• New hairs develop from cell division of the matrix in the bulb.


Structure of Hair

• Shaft -- visible– medulla, cortex & cuticle– CS round in straight hair– CS oval in wavy hair

• Root -- below the surface

• Follicle surrounds root– external root sheath– internal root sheath– base of follicle is bulb

• blood vessels• germinal cell layer


Structure of Hair






Structure of Hair






Hair Related Structures

• Arrector pili– smooth muscle in

dermis contracts with cold or fear.

– forms goosebumps as hair is pulled vertically

• Hair root plexus– detect hair movement

• sebaceous (oil) glands


Types of hair

• Lanugo is a fine, nonpigmented hair that covers the fetus.• Vellus hair is a short, fine hair that replaces lanugo• Course pigmented hair appears in response to androgens• Hair that appears in response to androgens and hair of the

head, eyelashes and eyebrows is known as terminal hair.


Hair removal

• Depilatories dissolve the protein in the hair shaft• Electrolysis uses an electric current to destroy the hair

matrix.


Hair Growth

• The hair growth cycle consists of a growing stage and a resting stage.– Growth cycle = growth stage & resting stage

• Growth stage – lasts for 2 to 6 years– matrix cells at base of hair root producing length

• Resting stage– lasts for 3 months– matrix cells inactive & follicle atrophies

– Old hair falls out as growth stage begins again• normal hair loss is 70 to 100 hairs per day

• Both rate of growth and the replacement cycle can be altered by illness, diet, high fever, surgery, blood loss, severe emotional stress, and gender.

• Chemotherapeutic agents affect the rapidly dividing matrix hair cells resulting in hair loss.


Hair Color

• Hair color is due primarily to the amount and type of melanin.

• Graying of hair occurs because of a progressive decline in tyrosinase.– Dark hair contains true melanin– Blond and red hair contain melanin with iron and sulfur

added– Graying hair is result of decline in melanin production– White hair has air bubbles in the medullary shaft

• Hormones influence the growth and loss of hair (Clinical applications).


Functions of Hair

• Prevents heat loss• Decreases sunburn• Eyelashes help protect eyes• Touch receptors (hair root

plexus) senses light touch


Glands of the Skin

• Specialized exocrine glands found in dermis

• Sebaceous (oil) glands• Sudiferous (sweat) glands• Ceruminous (wax) glands• Mammary (milk) glands


Sebaceous (oil) glands

• Sebaceous (oil) glands are usually connected to hair follicles; they are absent in the palms and soles (Figure 5.1 ).

• Secretory portion of gland is located in the dermis– produce sebum

• contains cholesterol, proteins, fats & salts• moistens hairs• waterproofs and softens the skin• inhibits growth of bacteria & fungi (ringworm)

• Acne– bacterial inflammation of glands– secretions are stimulated by hormones at puberty


Sudoriferous (sweat) glandsEccrine sweat glands have an extensive distribution most areas of skin

– secretory portion is in dermis with duct to surface– ducts terminate at pores at the surface of the epidermis.– regulate body temperature through evaporation (perspiration)– help eliminate wastes such as urea.

Apocrine sweat glands are limited in distribution to the skin of the axilla, pubis, and areolae; their duct open into hair follicles.– secretory portion in dermis– duct that opens onto hair follicle– secretions are more viscous

• Table 5.3 compares eccrine and apocrine sweat glands.


Ceruminous Glands

• Ceruminous glands are modified sudoriferous glands that produce a waxy substance called cerumen. – found in the external auditory meatus– contains secretions of oil and wax glands– barrier for entrance of foreign bodies

• An abnormal amount of cerumen in the external auditory meatus or canal can result in impaction and prevent sound waves from reaching the ear drum (Clinical Application).


Structure of Nails (Figure 5.5)

• Tightly packed keratinized cells• Nail body

– visible portion pink due to underlying capillaries

– free edge appears white• Nail root

– buried under skin layers– lunula is white due to thickened

stratum basale• Eponychium (cuticle)

– stratum corneum layer


Nail Growth

• Nail matrix is below nail root -- produces growth

• Cells transformed into tightly packed keratinized cells

• 1 mm per week

• Certain nail conditions may indicate disease (Figure 5.5b)


TYPES OF SKIN• Thin skin

– covers all parts of the body except for the palms and palmar surfaces of the digits and toes.

– lacks epidermal ridges– has a sparser distribution of sensory receptors than thick

skin.• Thick skin (0.6 to 4.5 mm)

– covers the palms, palmar surfaces of the digits, and soles– features a stratum lucidum and thick epidermal ridges– lacks hair follicles, arrector pili muscles, and sebaceous

glands, and has more sweat glands than thin skin.• Table 5.4 summarizes the fractures of thin and thick skin.


FUNCTIONS OF SKIN -- thermoregulation• Perspiration & its evaporation

– lowers body temperature– flow of blood in the dermis is adjusted

• Exercise– in moderate exercise, more blood brought to surface

helps lower temperature– with extreme exercise, blood is shunted to muscles and

body temperature rises

• Shivering and constriction of surface vessels– raise internal body temperature as needed


FUNCTIONS OF SKIN• blood reservoir

– extensive network of blood vessels

• protection - physical, chemical and biological barriers– tight cell junctions prevent bacterial invasion– lipids released retard evaporation– pigment protects somewhat against UV light– Langerhans cells alert immune system

• cutaneous sensations – touch, pressure, vibration, tickle, heat, cold, and pain arise

in the skin


FUNCTIONS OF SKIN• Synthesis of Vitamin D

– activation of a precursor molecule in the skin by UV light– enzymes in the liver and kidneys modify the activated

molecule to produce calcitriol, the most active form of vitamin D.

– necessary vitamin for absorption of calcium from food in the gastrointestinal tract

• excretion– 400 mL of water/day, small amounts salt, CO2, ammonia

and urea


Transdermal Drug Administration

• method of drug passage across the epidermis and into the blood vessels of the dermis– drug absorption is most rapid in areas where skin is thin

(scrotum, face and scalp)• Examples:

– nitroglycerin (prevention of chest pain from coronary artery disease)

– scopolamine ( motion sickness)– estradiol (estrogen replacement therapy)– nicotine (stop smoking alternative)


MAINTAINING HOMEOSTASIS: SKIN WOUND HEALING


Epidermal Wound Healing• Abrasion or minor burn• Basal cells migrate across the wound (Figure 5.6a)• Contact inhibition with other cells stops migration• Epidermal growth factor stimulates basal cells to

divide and replace the ones that have moved into the wound (Figure 5.6b).

• Full thickness of epidermis results from further cell division


Deep Wound Healing• When an injury extends to tissues deep to the epidermis, the repair process is more complex than epidermal healing, and

scar formation results.

• Healing occurs in 4 phases

– inflammatory phase has clot unite wound edges and WBCs arrive from dilated and more permeable blood vessels

– migratory phase begins the regrowth of epithelial cells and the formation of scar tissue by the fibroblasts

– proliferative phase is a completion of tissue formation

– maturation phase sees the scab fall off

• Scar formation

– hypertrophic scar remains within the boundaries of the original wound

– keloid scar extends into previously normal tissue

• collagen fibers are very dense and fewer blood vessels are present so the tissue is lighter in color


Deep Wound Healing

• Phases of Deep Wound Healing– During the inflammatory phase, a blood clot unites the

wound edges, epithelial cells migrate across the wound, vasodilatation and increased permeability of blood vessels deliver phagocytes, and fibroblasts form (Figure 5.6c).

– During the migratory phase, epithelial cells beneath the scab bridge the wound, fibroblasts begin scar tissue, and damaged blood vessels begin to grow. During this phase, tissue filling the wound is called granulation tissue.


Phases of Deep Wound Healing


Deep Wound Healing

• Phases of Deep Wound Healing– During the proliferative phase, the events of the

migratory phase intensify.– During the maturation phase, the scab sloughs off, the

epidermis is restored to normal thickness, collagen fibers become more organized, fibroblasts begin to disappear, and blood vessels are restored to normal (Figure 5.6d).

– Scar tissue formation (fibrosis) can occur in deep wound healing.


DEVELOPMENT OF THE INTEGUMENTARY SYSTEM

• Epidermis develops from ectodermal germ layer– Hair, nails, and skin glands are epidermal derivatives

(Figure 5.7).– The connective tissue and blood vessels associated with

the gland develop from mesoderm.• Dermis develops from mesenchymal mesodermal germ

layer cells


Development of the Skin

• Timing– at 8 weeks, fetal “skin” is

simple cuboidal– nails begin to form at 10

weeks, but do not reach the fingertip until the 9th month

– dermis forms from mesoderm by 11 weeks

– by 16 weeks, all layers of the epidermis are present

– oil and sweat glands form in 4th and 5th month

– by 6th months, delicate fetal hair (lanugo) has formed

• Slippery coating of oil and sloughed off skin called vernix caseosa is present at birth


Age Related Structural Changes

• Collagen fibers decrease in number & stiffen • Elastic fibers become less elastic• Fibroblasts decrease in number• decrease in number of melanocytes (gray hair, blotching)• decrease in Langerhans cells (decreased immune

responsiveness)• reduced number and less-efficient phagocytes


AGING AND THE INTEGUMENTARY SYSTEM

• Most of the changes occur in the dermis– wrinkling, slower growth of hair and nails– dryness and cracking due to sebaceous gland atrophy– Walls of blood vessels in dermis thicken so decreased

nutrient availability leads to thinner skin as subcutaneous fat is lost.

• anti-aging treatments– microdermabrasion, chemical peel, laser resurfacing,

dermal fillers, Botuliism toxin injection, and non surgical face lifts.

– Sun screens and sun blocks help to minimize photodamage from ultraviolet exposure


Photodamage

• Ultraviolet light (UVA and UVB) both damage the skin• Acute overexposure causes sunburn• DNA damage in epidermal cells can lead to skin cancer• UVA produces oxygen free radicals that damage collagen

and elastic fibers and lead to wrinkling of the skin


DISORDERS: HOMEOSTATIC IMBALANCES

• Skin cancer can be caused by excessive exposure to sunlight.

• Among the risk factors for skin cancer are skin type, sun exposure, family history, age, and immunologic status.– The three most common forms are – basal cell carcinoma, – squamous cell carcinoma, and – malignant melanoma.


Skin Cancer• 1 million cases diagnosed per year• 3 common forms of skin cancer

– basal cell carcinoma (rarely metastasize)– squamous cell carcinoma (may metastasize)– malignant melanomas (metastasize rapidly)

• most common cancer in young women• arise from melanocytes ----life threatening• key to treatment is early detection watch for

changes in symmetry, border, color and size• risks factors include-- skin color, sun exposure,

family history, age and immunological status


Burns

• Tissue damage from excessive heat, electricity, radioactivity, or corrosive chemicals that destroys (denatures) proteins in the exposed cells is called a burn.

• Generally, the systemic effects of a burn are a greater threat to life than are the local effects.

• The seriousness of a burn is determined by its depth, extent, and area involved, as well as the person’s age and general health. When the burn area exceeds 70%, over half of the victims die.


Burns

• Destruction of proteins of the skin– chemicals, electricity, heat

• Problems that result– shock due to water, plasma and plasma protein

loss– circulatory & kidney problems from loss of

plasma– bacterial infection

• Two methods for determining the extent of a burn are the rule of nines and the Lund-Bowder method (Figure 5.10).


Burns


Types of Burns

• First-degree– only epidermis (sunburn)

• Second-degree burn – destroys entire epidermis & part of dermis – fluid-filled blisters separate epidermis & dermis– epidermal derivatives are not damaged– heals without grafting in 3 to 4 weeks & may scar

• Third-degree or full-thickness– destroy epidermis, dermis & epidermal derivatives– damaged area is numb due to loss of sensory nerves


Burns


Pressure Sores

• Pressure ulcers, also known as decubitus ulcers– caused by a constant deficiency of blood to

tissues overlying a bony projection that has been subjected to prolonged pressure

– typically occur between bony projection and hard object such as a bed, cast, or splint

– the deficiency of blood flow results in tissue ulceration.

• Preventable with proper care


end

Chapter 5

Documents

skin figure

epidermis figure

skin color

skin graft

introductionthe skin

new skin

keratinocytes figure

keratinocytes stem cells