The Integumentary System

Skin and its accessory structures, sweat and oil glands, hair, nails,

muscles and nerves

Skin• A large organ composed of all 4 tissue types• 22 square feet • Weight 10 lbs.• 7% of total body weight• 1.5mm-4mm thick• Two distinct regions

– Epidermis• Epithelial cells, avascular

– Dermis• Fibrous connective tissue, vascularized

hair shaftstratum corneum

dermal papilla

Meissner’s corpuscle (touch)

blood vessels

sebaceous gland

arrector pili muscle

sweat gland

hair follicle

adipose tissue (usually in subcutaneous area)Pacinian corpuscle (deep pressure)

dermis

epidermis

SKIN

Epidermis

• Superficial, thinner part of skin

• Epithelial tissue- keratinized stratified squamous epithelium

• avascular (contains no blood vessels)

Overview of Epidermis

• Stratified squamous epithelium

– 4 types of cells-Keratinocytes, melanocytes, langerhans cells and merkel cells

– 5 distinct strata (layers) of cells

Cells of EpidermisKeratinocyte• 90% of epidermal cells• Produce keratin, fibrous

protein that gives skin its protective properties

• many desmosomes• Mitosis at basal layer and

dead at apical layer• Rub off millions daily,

new epidermis every 25-45 days

Cells of Epidermis

Melanocyte• Spider-shaped cell that makes

pigment Melanin• In deepest layer, sending

processes into other layers to deliver melanin

• Accumulates melanin in melanosomes that are taken up by keratinocyte

• Melanin accumulates on sunny side of keratinocytes creating a pigment shield that protects nucleus from damaging UV radiation

Cells of Epidermis

Langerhans Cells• Phagocytes that ingest

foreign substances and help activate the immune system

Cells of Epidermis

Merkel Cells• Occasional cells found in

deepest layers of epidermis at epidermal-dermal junction

• In contact with a disclike sensory nerve ending forming a merkel disc that functions as sensory receptor for touch

Several Distinct layers of keratinocytes in various stages of development form epidermis

Layers (Strata) of the Epidermis-a continuum of cell growth as move up the layers

• Stratum corneum

• Stratum lucidum

• Stratum granulosum

• Stratum spinosum

• Stratum basale

Stratum Basale (stratum germinativum)• Deepest layer,single layer of

mitotically active cells attached to dermis

• Youngest keratinocytes• Large nuclei• 10-25% of cells are

melanocytes• Occasional merkel cells• Desmosomes and

hemidesmosomes

Stratum Basale

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

Stratum Spinosum (prickly layer)

• 8-10 cell layers

• Cells held together by desmosomes which gives cells a spiny or irregular appearance during tissue preparation

• Langerhans cells present

• Projections of melanocytes

Stratum Granulosum• Transition between

metabolically active strata and the dead cells of the more superficial strata

• Thin, 3-5 layers of flat dying cells that show nuclear degeneration and cells flatten

• lamellar granules that have a waterproofing glycolipid that gets released into extracellular space to slow water loss from dermis

• Contain dark-staining keratohyalin granules that will help form keratin in upper layers

Stratum Lucidum

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

• Three to five layers of clear, flat, dead cells that form a thin translucent band

Stratum Corneum

• Outermost layer

• ¾ thickness of epidermis

• 25 to 30 layers of flat dead cells filled with keratin and surrounded by glycolipids

• Barrier to light, heat, water, chemicals & bacteria, protect against abrasion and penetration

Keratinization and Growth of Epidermis

• New cells formed in stratum basale and pushed to surface

• Keratinization- accumulate keratin as move up through the layers

• Aptosis• Slough• 4 week process

Dermis

• Deeper, thicker part of skin

• Strong flexible connective tissue

Papillary Dermis• Thin superficial layer• Top 20% of dermis• Aerolar connective tissue with

collagen fibers and fine elastic fibers

• Very vascular• Dermal Papillae

– Small peg-like projections into epidermis that increase the surface area

– Capillary loops– Free nerve endings (pain

receptors)– Meissner corpuscles that are

touch receptors

Reticular Dermis

• 80% of thickness of Dermis

• Dense irregular connective tissue with a matrix of thick bundles of interlacing collagen fibers

• Provides strength, extensibility & elasticity to skin

Dermis

• Epidermal Ridges are downward projections of epidermis into dermis between the dermal papillae of the papillary region creating ridges and grooves that increase friction and enhance grip– Fingerprints and footprints– Genetically determined,

unique and do not change throughout life

Dermis

• Lines of cleavage in the skin/skin tension lines indicate the predominant direction of the underlying collagen fibers. – Important for surgical

incision planning– Incision parallel to

them provides best scar

Blisterseparation of dermis and epidermis by fluid accummulation

Stretch Marks

• Tears in dermis• White scars• striae

SkinCallus- abnormal thickening of skin due to exposure to friction

HypodermisAKA subcutaneous layer, subQ, superficial fascia

• Not part of the skin• Deep to dermis• Consists of areolar and

adipose tissue• Functions to store fat,

absorb shock, insulator, anchors skin to underlying structures and contains lamellated (pacinian corpuscles) nerve endings for pressure

Basis of Skin Color3 pigments

• Melanin– Only pigment made in skin– Yellow to reddish brown– Synthesis depends on enzyme tyrosinase in melanocytes, UV light

increases activity of enzyme– Difference in color due to amount and kind of melanin and not

number of melanocytes– Pheomelanin- yellow to red– Eumelanin- brown to black– Freckles and moles are local accumulations of melanocytes– Albinism- inherited inability to produce melanin, melanocytes can

not synthesize tyrosinase– Vitiligo is partial or complete loss of melanocytes from patches of

skin resulting in irregular white spots due to immune malfunction

Basis of Skin Color3 pigments

• Hemoglobin– Oxygen carrying pigment in RBC– In dermal capillaries

• Carotene– Yellow to orange pigment found in plant products– Precursor of vitamin A that is used to synthesize

pigments needed for vision– Excessive amounts accumulate in stratum corneum and

fatty areas of dermis and sub Q, in palms and soles

Skin Color and Diagnosis

• Cyanotic– Skin of nail beds and

mucus membranes bluish due to poorly oxygenated hemoglobin

• Jaundice– Build up of bilirubin in

skin, yellow pigment– Liver disease

• Erythema– Redness due to

engorgement of capillaries of dermis with blood due to injury, heat, infection, inflammation or allergic reactions

• Pallor– Low blood pressure, shock,

anemia

• Bruises– Black and blue marks due

to blood that escapes circulation and clots beneath skin-hematomas

Accessory Structures of Skin skin appendages

• develop from the embryonic epidermis

• Cells sink inward during development to form:– Hair and hair follicles

– sebacious (oil) glands

– sweat glands

– nails

Glands of Skin

• Sebaceous (oil) glands

• Sudoriferous (sweat) glands

• Ceruminous glands

Sebaceous(oil) Glands• Secreting portion in dermis

• Opens onto the hair follicle

• Absent in palms and soles

• Secrete sebum

– Cells accumulate lipids until they burst, holocrine glands

– Sebum is lipids and cell fragments

– Softens and lubricates skin and hair, prevents brittleness

– bactericidal

Sebaceous(oil) Glands

• Whiteheads –sebaceous gland duct blocked and sebum accumulates

• Blackhead when the material oxidizes or dries

• Acne-inflammation of these glands, colonized by bacteria

Sudoriferous (sweat) Glands

• Release sweat onto hair follicles or onto skin surface through pores

• Eccrine• apocrine

Eccrine Sweat Glands• Excretory duct ends at pore on surface of epidermis• Most numerous on palms, sole of feet and forehead• Sweat- 99% water, salts, vit C, antibodies, microbe killins

peptide, dermicidin and trace metabolic wastes, acidic • Regulated by nervous system• Function to regulate body temperature and eliminate

wastes• Insensible sweat and sensible sweat

Apocrine Sweat Glands

• Ducts open to hair follicles• Secretory product like sweat but has lipids and

proteins, odorless but takes on odor when organic molecules decomposed by bacteria on skin

• Axillary and anogenital areas• Function at puberty but precise function not

known and no role in thermoregulation

Ceruminous Glands

• Modified apocrine sweat glands in external ear• Produce a waxy substance• Cerumen-earwax is combined secretion of

ceruminous glands and sebaceous glands, deters insects and blocks entry of foreign materials

Hair

• Hair is columns of dead keratinized cells bonded together by extracellular proteins

• On entire skin surface except palms, soles, lips, nipples and parts of external genitalia

• Shaft-portion that project above skin surface• Root-embedded in skin, penetrates into dermis or

subQ• Hair Follicle- surrounds the root• Bulb-base of hair follicle

Structure of Hair• Shaft – visible• Root -- below the surface• Follicle surrounds root• base of follicle is bulb

• blood vessels

• Mitotically active cells

Structure of Hair Follicle

• About 4mm below skin surface, expanded bulb

• Knot of sensory nerve endings called hair follicle receptor or hair root plexus wrap around the bulb and are stimulated by bending of hairs, hairs sensitive to touch

Hair Follicle

• Papilla of hair-dermal tissue that protrudes into hair pulp and contains capillaries

• Matrix- actively dividing cells

Figure 5.5c

Structure of HairShaft – visible

– 3 concentric layers of keratinized cells

• Medulla– Central core, large cells and

air spaces• Cortex

– Bulky layer around medulla, several layers of flattened cells

• Cuticle– Outermost layer, single layer

of cells that overlap one another from below like roof shingles

Figure 5.5a, b

Hair Pigment

• Hair pigment made by melanocytes at base of hair follicle and transferred to cortical cells

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

Hair Related Structures• Arrector pili

– smooth muscle in dermis contracts with cold or fear.

– forms goosebumps as hair is pulled vertically, into upright position

• Hair root plexus– detect hair movement

• sebaceous (oil) glands

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

– With age, hair not replaced as fast as shed leading to thinning and baldness(alopecia)

• 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.

Functions of Hair• Prevents heat loss• Decreases sunburn• Eyelashes help protect

eyes• Touch receptors (hair

root plexus) senses light touch

Nails• Plates of tightly packed, hard, dead keratinized

epidermal cells that form a clear, solid covering over the dorsal surfaces of the distal portions of digits

• Nail body-visible portion of nail

• Free Edge- part that extends past distal aspect of digit

• Hyponychium- region below free edge

• Nail Root- proximal part buried beneath nail fold

• Lunula-white crescent, too thick to see vasculature

• Eponychium- cuticle

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.

Skin Cancer

• The three major types of skin cancer are:– Basal cell carcinoma– Squamous cell carcinoma– Melanoma

Basal cell and Squamous cell considered nonmelanoma skin cancers. In 2008, more than 1,000,000 new cases in US but less than 1,000 deaths.

Basal Cell Carcinoma

• Least malignant and most common skin cancer• cells at base of epidermis proliferate and invade

the dermis and hypodermis• Sun-exposed areas• Dome-shaped nodules that develop a central

ulcer with a pearly, beaded edge• Slow growing and do not often metastasize• Can be cured by surgical excision in 99% of the

cases

Basal Cell Carcinoma

Basal Cell Carcinoma

Three common presentations:

Small, smooth, pale, or waxy shiny lump

Firm, red lump A lump that bleeds or develops a crust

Basal Cell Carcinoma

Squamous Cell Carcinoma

• Arises from cells of epidermis• Arise most often on scalp, ears, and lower lip• Scaly reddened papule• Grows rapidly and metastasizes if not removed• Prognosis is good if treated

Squamous Cell Carcinoma

Squamous Cell Carcinoma

Melanoma

• Cancer of melanocytes is the most dangerous type of skin cancer because it is:– Highly metastatic– Resistant to chemotherapy

Melanoma

A form of skin cancer that arises in melanocytes, the cells that produce pigment and also are found in the epidermis.

Melanomas usually begin in a mole, which is a benign cluster of melanocytes and other tissue.

Normal moles:

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Signs and Symptoms of Melanoma

Change in the size, shape or color of a mole, such as:

– Signs that a mole’s border is becoming more ragged

– Spread of pigmentation beyond its border

Scaliness, bleeding or change in the appearance of a bump or nodule

Change in sensation, itchiness, tenderness or pain in a mole or other growth

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– A (Asymmetry) one portion of the mole does not match the other

– B (Border) edges are irregular, notched, or blurred

– C (Color) different shades of black or brown, patchy colors

– D (Diameter) spot is 6 millimeters across, or growing larger

A B

C D

Use ABCD Rule to Spot Melanoma

Melanoma (the A-B-C and Ds)

Asymmetry -- The shape of one half does not match the other.

AsymmetryOne half does not match

the other half.

Border irregularityThe edges are ragged, notched,

or blurred.

Melanoma (the A-B-C and Ds)

Color -- The color is uneven. Shades of black, brown, and tan may be present. Areas of white, grey, red, pink, or blue also may be seen.

Melanoma (the A-B-C and Ds)

Diameter -- There is a change in size, usually an increase. Melanomas are usually larger than the eraser of a pencil (5 mm or 1/4 inch).

Diameter -Greater than ¼ inch. Any sudden or continuing increase in size is of special concern.

Normal Mole

Malignant Mole

Melanoma

May be found when a pre-existing mole changes:Early changes- forming a new black area- newly formed fine scales- itching in a moleMore advanced changes- texture changes (becomes hard or lumpy)- itch, ooze, or bleed- usually do not cause pain

Melanoma

• Moles are clusters of melanocytes, called nevus (singular) and nevi (multiple)

• Most people have 10-40 that appear at birth or after birth, usually before age 40

• Increased risk of melanoma in those with more than 50 or in person with dysplastic nevi (abnormal looking moles)

Melanoma• US- more than 53,600 people learned they had

melanoma in 2008• Risk factors:

– Fair skin– More than 50 moles– Dysplastic moles– About 10% of patients with melanoma have a family

history– Depressed immune system– UV radiation– Blistering sunburn

Melanoma

• Treated by wide surgical excision accompanied by immunotherapy

• Chance of survival is poor if the lesion is over 4 mm thick

Wear your Sunblock!!!

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• First-degree – only the epidermis is damaged

– Symptoms include localized redness, swelling, and pain

• Second-degree – epidermis and upper regions of dermis are damaged– Symptoms mimic first degree burns, but blisters also

appear– fluid-filled blisters separate epidermis & dermis– Heals in 3 to 4 weeks & may scar

Burns

Third-degree – entire thickness of the skin is damaged

– Burned area appears gray-white, cherry red, or black; there is no initial edema or pain (since nerve endings are destroyed)

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

Burns

Rule of Nines

• Estimates the severity of burns

• Burns considered critical if:– Over 25% of the body has second-degree burns– Over 10% of the body has third-degree burns– There are third-degree burns on face, hands, or

feet

Rule of Nines

Figure 5.8a

Wound Healing

• Two types depending on the depth of the wound

• Epidermal Wound Healing

• Deep Wound Healing

Epidermal Wound Healing• Abrasion or minor burn

• Basal cells migrate across the wound

• 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

• Full thickness of epidermis results from further cell division

Deep Wound Healing

• In response to an injury that extends into the dermis and subQ

• Scar tissue is formed• Four Phases

– Inflammatory– Migratory– Proliferative– Maturation

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

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.