Ch 5: The Integumentary System

General info– Integumentary system –

• skin, sweat and oil glands, hairs and nails

– Skin –• Weighs: 9-12 pounds• 7% of total body weight• Integument = covering • Composed of:

– Epidermis

» Epithelial cells (relies on dermis below for nutrients)

» Outermost protection

– Dermis

» Most of the skin

» Tough layer

» Fibrous connective tissue

– Hypodermis

» Deep to the skin

» Adipose & areolar tissue – grows with weight gain

» Anchors the underlying tissue

Figure 5.1

Epidermis

Dermis

Hypodermis(superficialfascia)

Hair root

Hair shaft

Pore

Dermal papillae (papillary layer of dermis)

Meissner's corpuscle

Free nerve endingReticular layer of dermis

Sebaceous (oil) gland

Arrector pili muscle

Sensory nerve fiberEccrine sweat gland

Pacinian corpuscle

Artery

Vein

Adipose tissue

Hair follicle receptor(root hair plexus)

Hair follicle

Eccrine sweatgland

Epidermis• Made of:

– Keratinized stratified squamous epithelium consisting of four distinct cell types and four/five distinct layers

• Cells:– Keratinocytes

• Majority of epidermal cells, produce a fibrous protein – keratin – protection

• Arise in the deepest part of the epidermis (stratum basale) – undergoes continuous mitosis

• As they are pushed up they produce keratin• When they reach the surface they are dead and scale

like keratin filled plasma membranes• New epidermis every 25 – 45 days• Friction can cause a thickening of the epidermis = a

callus

Cells cont.• Melanocytes –

– Spider shaped epithelial cells that synthesize the pigment melanin

– Production and movement –• Melanin is moved to the melanocyte’s

processes to be periodically transferred to keratinocytes

• Accumulate on the superficial side of keratinocytes nucleus

• Forms a pigment shield that protects the nucleus from UV radiation

Cells cont.

• Langerhans’ cells –

– Epidermal dendritic (projections) cells

– Processes extend around the keratinocytes to form a continuous network

– Arise from bone marrow migrate to epidermis

– Composed of macrophages that help activate the immune system

Cells cont.

• Merkel cells–

– Present at epidermal-dermal junctions

– Shape = spiky hemisphere

– Closely associated with sensory nerve endings• Sensory nerve endings + Merkel cells = Merkel

discs = sensory receptors for touch

Layers – general info• Epidermis - five layers or strata - “bed

sheets”• Deep to superficial the layers (for thick skin)

are:– Stratum basale– Stratum spinosum– Stratum granulosum– Stratum lucidum (absent in thin skin)– Stratum corneum

• Thick skin covers the palms, fingertips, and soles of the feet.

Layers of Epidermis

• Stratum Basale –– Basal layer – deepest epidermal layer, site of

mitosis (renews the cell population)– Firmly attached to dermis – wavy borderline– Single row of cells = youngest keratinocytes– Alternative name = stratum germinativum

(germinating layer)

– 10-25% of cells are melanocytes – branches will stretch into the more superficial stratum spinosum layer

Layers of the Epidermis cont. • Stratum Spinosum –

– Prickly layer– Multiple cell layers thick – Contains:

• Keratinocytes• melanin granules• highest concentration of Langerhans’ cells

– Keratinocytes –• Irregular giving the layer its prickly appearance• Occurs when the cells shrink but the desmosomes

hold tight– Melanin granules and Langerhans’ cells –

scattered among the keratinocytes

Layers cont. • Stratum Granulosum –

– 3-5 cell layers – Granular layer –

• Help to form keratin

– Keratinocytes undergo a great deal of physical changes – turn them into the tough outer cells of the epidermis

– Thickens because cytosol proteins bind to inner membrane face & lamellated granules coat the outer surfaces

– Lamellated granules –• Contain a waterproofing glycolipid • Slows water loss across the epidermis

Layers cont.

• Stratum lucidum –

– Clear layer

– Found only in thick skin and is composed of dead keratinocytes

– Clear, flat, dead keratinocytes w/ no distinct boundaries

Layers cont.

• Stratum corneum –– Horny layer– Outermost protective layer – composed of a

thick layer of dead keratinocytes– ¾ of the epidermal thickness – Keratin & thickened plasma membranes

protect the skin against abrasions – Glycolipids between the cells waterproofs

the layer– Dandruff from scalp & dry skin slough off –

shed 40 lbs of dead flakes in lifetime

Dermis• 2nd major skin layer • Composed of:

– Connective tissue proper – Fibroblasts, macrophages, mast cells, white blood

cells – Matrix embedded w/ collagen, elastin & reticular fibers

• Supplied w/ nerve fibers, blood vessels, & lymphatic vessels

• Hair follicles, oil, & sweat glands reside in the dermis

Dermal layers

• 2 layers –– Papillary & Reticular– Papillary –

• Superficial layer• Highly vascularized areolar connective tissue –

– Containing a woven mat of collagen and elastin fibers

• Dermal papillae – – Superior surface– Indent the overlying epidermis – Hands & feet – lie atop larger mounds – dermal ridges –

elevate the overlying epidermis – epidermal ridges – increase friction & enhance gripping ability of hands and feet

– Genetically determined ridges – Fingerprints – the identifying film that is left from the sweat that

seeps from the pores along the crests

• Meissners corpuscles – nervous pain receptors

Dermal layers – Reticular layers –

• 80% of the thickness of the dermis • Dense irregular connective tissue • Matrix –

– Thick bundles of interlacing collagen fibers – most run parallel to skin surface

• Lines of cleavage or tension lines – Run longitudinally– Externally invisible – Important for surgery – skin gapes less when incisions are

made parallel to the lines

• Flexure lines –– Dermal folds that occur at or near joints where the dermis is

secured to deeper structures– Accommodates joint movement– Deep creases in the palms

Cleavage Lines Flexure Lines

Skin Pigments

• Skin color is determine by three pigments:– Melanin –

• Only pigment (of the three) made in the skin• A polymer – tyrosine amino acid• Color = yellow – black• Process-

– Melanocytes synthesize tyrosinase

– Increased activity when exposed to UV radiation– Melanin build up (a tan) helps protect our DNA –

absorbs the light and dissipates the energy as heat

• Skin color determined by the kind and amount of melanin made and retained

• Freckles = accumulations of melanin

Skin pigments – Hemoglobin

• Fair skinned people –• Color = provides a pinkish hue due to oxygenated

blood• Common in Caucasians – small amounts of

melanin – epidermis is almost transparent – allows hemoglobin’s color to show through

– Carotene• Color = yellow – orange • Accumulates in the stratum corneum & fatty tissue

of hypodermis• Obvious: palms and soles of the feet where

corneum is the thickest & when carotene rich foods (carrots) are eaten in large amounts

Discolorations of the skin

• Erythema:– Skin reddening – Blood vessels of the dermis dilate

• Pallor/blanching:– Paling of the skin due to stress, fear, low bp, or

anemia

• Jaundice:– Can indicate a liver disorder– Yellow bile pigments accumulate in the blood –

deposited in tissues

Discolorations of the skin cont.

• Bronzing:– Addison’s disease – metallic

appearance of the skin– Increased production and

functions of the adrenal cortex

• Bruises:– Blood escaping from circulation

and accumulating beneath the skin

– Clotted blood = hematoma – “blood swelling”

Appendages of the skin • Appendages =

– hair & hair follicles, nails, sweat glands, & oil glands

• Sweat glands/sudoriferous glands -

– Sudor = sweat– Distributed over entire body except nipples &

external genitalia– ~ 2.5 million sweat glands per person

– Two types:

• Eccrine & Apocrine

Glands • Eccrine sweat glands –

– AKA merocrine sweat glands– Produce true sweat– Most numerous of the sweat glands

• Abundant on palms of hands, soles of the feet and the forehead

– Simple, coiled, tubular gland– Duct extends to the open, skin surface, through a funnel

– pore – Sweat is released by exocytosis

• 99% water• Salts, antibodies, dermicidin, metabolic wastes, vit C, lactic acid

(attracts mosquitoes)• Components depend on heredity and diet• Controlled by sympathetic nervous system – no control• Prevents over heating of the body – begins on forehead &

spreads inferiorly• Anxiety sweat begins on palms, soles of feet and armpits then

spreads

Glands

• Apocrine sweat glands –– Confined to the armpits & genital areas – Produce true sweat with the addition of fatty

substances & proteins – Larger than eccrine glands– Ducts empty into the hair follicles – Very viscous & can appear milky or yellow– Secretion is odorless – organic molecules are

decomposed by bacteria on the skin = odor – Induced by androgens (hormones)

Glands

• Ceruminous glands –– Modified sweat glands – Lines the ear canal – secretes sticky, bitter

substance – ear = cerumen • Thought to deter insects and block foreign

materials

• Mammary glands –– Modified sweat glands– Found in breasts– Produce milk

Sebaceous Glands

• Simple branched alveolar glands - found everywhere except palms of hands and soles of feet

• Secrete:– Sebum (oily secretion – lipids and cell

fragments)• Secreted into hair follicle – occasionally to a pore

on the skins surface• Soften and lubricates the skin & hair • Slows water loss from the skin when external

humidity is low• Kills bacteria• Stimulated by hormones – androgens• Active during puberty

Hair

• Hair is found everywhere except…– Palms, soles of our feet, lips, nipples, and

parts of our external genitalia

• Main functions: – sensing, sunlight protection, heat loss, filters,

& shields

Hairs cont• Hairs, or pili, are flexible strands produced by hair

follicles that consist of dead, hard, keratinized cells– Benefits of hard keratin

• Tough and durable• Individual cells don’t slough off

• Regions of the hair:– 2 main regions

• Shaft– Projects from the skin

– Round shaft/pore = straight

– Oval shaft/pore = silky & wavy

– Flat shaft/pore = kinky

• Root – Embedded in the skin

– Area where hair develops & grows

Hair cont• Three concentric layers of keratinized cells:

– Medulla:• Inner core• Consists of large cells & air spaces• Absent in fine hairs

– Cortex: • Middle layer• Bulky layer surrounding the medulla• Several layers of flattened cells

– Cuticle: • Outer layer• Heavily keratinized • Single layer of cells that overlap one another• Arrangement helps keep hair apart• Provides strength

Hair

Hair cont– Split ends =

• When cuticle wears away & allows the cortex & medulla to “frizz” out

– Hair pigments (melanin of different colors) are made by melanocytes at the base of the hair follicle

• Melanin colors combine to produce the hair color• Grey or white hair is due to decreased melanin

production & melanin granules being replaced by air bubbles in the hair shaft

Melanocytes

Structure of hair • Hair follicles reside in the dermis

– Fold down from the epidermis into the dermis & occasionally into the hypodermis

• Deep end of the hair follicle is expanded, forms hair bulb -surrounded by a knot of sensory nerve endings = root hair plexus (hair follicle receptor) – enables the hair to be a sense receptor

• Hair papilla – – Hair matrix = actively dividing area of the hair bulb =

produces hair – Supplies nutrients to the growing hair

• Wall of hair follicle:– Outer thick connective tissue root sheath – derived from

dermis – Inner epithelial root sheath – derived from epidermis

Structure of hair cont.

• Arrector pili – – “raiser of hair”– Smooth muscle cells associated with each

hair follicle– Pulls hair into an upright position – Dimples the skin in response to cold or fear

• Used for heat retention

Types of hair

• Hair classified as vellus or terminal• Vellus:

– Vell – “wool” or “fleece”– Women & children (peach fuzz) – Pale, soft hair– Stomach & face

• Terminal:– Coarser– Longer & darker than vellus hair– Eyebrows, scalp, axillary, & pubic regions in both

sexes– Face & chest of males– Growth due to androgens (in males – testosterone)

Homeostatic imbalances

• Hair growth influenced by nutrition & hormones– Poor nutrition = poor hair growth

• Rate of hair growth influenced by sex & age - varies from one body region to another (about 2 mm a week)– Growth cycles – includes an active phase & resting

phase– Follicles can become inactive for months at a time– Can lose up to 90 scalp hairs a day– Eyebrows = active for 3-4 months – inhibits long

eyebrow hairs– Eyelashes = slowest growing cycle

Homeostatic imbalances

• Baldness/hair thinning due to….– After 40, hairs are not replaced as fast, longer resting

phase• Alopecia = hair thinning

– Terminal hair is replaced by vellus hair

– Genetics = true or frank baldness• Male pattern baldness - sex-influenced trait• Gene is turned on during adulthood - inhibits hair follicles

response to testosterone – shortens hair growth cycles

– Homeostatic imbalances• Emotional trauma, fever, surgery, protein-deficient diets, &

lactation• Can be reversed if imbalances are corrected• Severe burns & radiation – hair loss is permanent because

the follicle was eliminated

Nails• Scale-like modification of the epidermis that forms a clear,

protective covering• Contain:

– hard keratin, a free edge, body (visible attached portion) & proximal root (embedded in skin)

• Nail bed –– deeper epidermal layer that extends beneath the nail– Nail itself corresponds to the superficial keratinized layers

• Nail matrix – – nail bed responsible for nail growth– Appear pink due to rich blood supply of capillaries

underlying the dermis• Lunula –

– little moon – lies over thick nail matrix – appears white• Nail folds –

– overlap of skin folds on the proximal and lateral borders• Cuticle –

– nail fold that projects onto the nail body

Nails

Functions • Functions of Integumentary system - • Protection

– Chemical barrier• Skin secretions & melanin• Low pH of skin secretions inhibits skin bacteria from

multiplying out of control• Antibacterial substances in sebum that kill bacteria

– Physical/mechanical barrier• Continuity of skin

– Waterproofing glycolipids block diffusion of H2O & H2O soluble substances

» Lipid soluble substances (O2, CO2, & fat soluble vitamins) will penetrate in small amounts

– Biological barriers• Langerhan’s cells – epidermis • Macrophages – dermis – dispose of viruses & bacteria that

may have penetrated the epidermis

Functions cont.• Body temp regulation –

• sweat glands to cool the body• constriction or dilation of capillaries

• Cutaneous sensation –– Cutaneous sensory receptors – part of the nervous system

• Respond to stimuli outside the body• Meisner’s corpuscles, Merkel discs, Pacinian receptors, & root hair

plexuses

• Vit D production – – Occurs when skin is exposed to sunlight – Needed for calcium absorption

• Blood reservoir –– Holds around 5% of the body’s blood– May be diverted to other areas when needed

• Nervous system constricts dermal vessels when other areas need blood

• Nitrogenous waste –– Skin excretes limited amounts of nitrogenous waste

• Ammonia, urea, & uric acid

Homeostatic imbalances • Skin cancers:

– Basal cell -• Most common skin cancer – sun exposure • 30% of all Caucasians in their lifetime • Cells in the stratum basale layer invade the dermis &

epidermis • Shiny, dome shaped nodules that develop a central ulcer• Metastasis seldom occurs

– Squamous cell -• Grow rapidly – will metastasize if not treated • Arise from keratinocytes in the stratum spinosum • Scaly reddened elevated lesion

– Melanoma -• Most dangerous • Highly metastatic & resistant to chemotherapy • Cancer of melanocytes • Develop from preexisting moles or areas w/ high pigment • Spreading brown/black patch - will spread to surrounding

lymph & blood vessels

A: basal cell, B: Squamous cell, C: Melanoma

Burns• A burn is:

– Tissue damage inflicted by intense heat, electricity, radiation, or certain chemicals, all of which denature cell proteins and cause cell death to infected areas

• Threats to patients:– Most immediate threat = dehydration & electrolyte

imbalance due to fluid loss• Renal failure and circulatory shock can occur• Infection becomes threat

– Burned skin is sterile for 24 hours

– Bacteria, viruses, & fungi invade the area and thrive in the dead tissue

• Rule of nine = body divided into 11 areas - each account for about 9% of the body’s total area – method for determining how much of the body surface has been burned

Rule of Nines

Burns cont.• First degree –

– Damage only to the epidermis – Redness, swelling, & pain– Heal w/in 2-3 days– Sunburn – partial thickness burn

• Second degree –– Injure epidermis & upper regions of the dermis– Symptoms similar to 1st degree, include blisters – Heal w/in 3-4 weeks w/ little or no scaring– Need to be mindful of the possibility of infections– Partial thickness burn

• Third degree –– Involve entire thickness of skin– Grey-white, cherry red, or blackened– Initially no edema – Not painful – nerve endings have been destroyed – Skin grafting is usually necessary

B: First degree

C: Second degree

D: Third degree

Developmental aspects• Epidermis develops from:

– Embryonic ectoderm• Dermis & hypodermis develop from:

– Mesoderm• Development:

– 4th month - skin is well formed– During adolescence, skin & hair become oilier as sebaceous glands are

activated– Optimal skin appearance – 20s & 30s– Approach of old age:

• Epidermal cell replacement slows• Adipose tissue diminishes• Elastic fibers clump • Collagen fibers stiffen • Wrinkles = loss of subcutaneous tissue (adipose tissue) & decrease in

elasticity

– Skin thins• Becomes more prone to bruising & other injuries

– Hair thins due to inactive hair follicles & activation of genes responsible for balding