Unit 4 – The Unit 4 – The Integumentary SystemIntegumentary System

Integumentary SystemIntegumentary SystemAlso known as the Integument

◦Accounts for 16% of your body weight

◦First line of defense◦Almost 2m2

Consists of 2 major components◦Cutaneous membrane◦Accessory structures

Integumentary SystemIntegumentary SystemCutaneous membrane has two

layers◦Epidermis◦Dermis

Accessory structures include:◦Hair◦Nails◦Exocrine glands

Integumentary SystemIntegumentary SystemBlood vessels and nerves are

found in the dermis

Deep to the dermis, is the subcutaneous layer (hypodermis)

Integumentary SystemIntegumentary SystemFunctions of skin and

subcutaneous layer:◦Protection◦Excretion◦Maintenance of body temperature◦Synthesis if vitamin D◦Storage of fats◦Detection of touch, pressure, pain,

temperature

THE EPIDERMISTHE EPIDERMISIntegumentary System

The EpidermisThe EpidermisStratified squamous epithelial tissue

◦Mostly keratinocytes (contains keratin)Is comprised of several layers (deep

to superficial) Stratum germinativum Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum

Thin Skin – covers most of your body

Thick skin – palms of hands, soles of feet

Epidermal LayersEpidermal LayersStratum germinativum

◦Deepest layer◦Attached to basal lamina◦Has epidermal ridges

Extend into dermis to strengthen bond between epidermis and dermis

Pattern of ridges are revealed in fingerprints◦Dominated by basal cells (germinative)

Stem cells that replace lost superficial cells◦Contains melanocytes – cells that make

melanin

Epidermal LayersEpidermal LayersStratum spinosum

◦8-10 layers of cells◦Made of freshly divided basal cells

Epidermal LayersEpidermal LayersStratum granulosum

◦“grainy layer”◦3-5 layers of cells pushed

superficially from stratum spinosum◦Make large amounts of keratin

Basis of hair and nails in humans Makes skin waterproof

◦Cells die in this layer

Epidermal LayersEpidermal LayersStratum lucidum

◦Found in the palms of your hands and soles of your feet

Epidermal LayersEpidermal LayersStratum corneum

◦The exposed surface of the skin◦15-30 layers of keratinized cells

It takes 15-30 days for cells to move from the stratum germinativum to the stratum corneum

Cells spend about 2 weeks in the stratum corneum before being shed

Epidermal LayersEpidermal LayersStratum corneum (con’t)

◦Is water resistant, but not waterproof Water evaporates at a rate of about

500ml/day Called insensible perspiration

Sweat glands produce sensible perspiration

◦Blisters are formed when the connections between superficial and deeper layers are damaged. Fluid collects between layers

THE DERMISTHE DERMISIntegumentary System

The DermisThe DermisLies between the epidermis and

the subcutaneous layerTwo major components

◦Superficial papillary layer◦Deeper reticular layer

The Papillary LayerThe Papillary LayerSuperficial portion of dermisAreolar tissueContains capillaries, lymphatics,

and sensory neurons that supply the surface of the skin

Contain dermal papillae that interlock with the epidermal ridges

Reticular LayerReticular LayerDeeper portion of dermisDense irregular connective tissue

◦Collagen and elastic fibersContains all cells of connective

tissue properAlso contains blood vessels,

lymph vessels and nerve fibers

Dermal Strength and Dermal Strength and ElasticityElasticityDermis contains both collagen and

elastic fiber◦Allows dermis to tolerate limited

stretching

Water also helps with flexibility and resilience◦Pinch test for dehydration

Aging, hormones, UV radiation damages elastic fibers◦Leads to wrinkles and sagging skin

Dermal Strength and Dermal Strength and ElasticityElasticityExtensive stretching of dermis can

exceed the elastic capabilities of the skin◦Complete recoiling of fibers is

prevented◦Result is stretch marks

Retin-A (derivitave of Vitamin A) can help repair the dermis and can lessen appearance of wrinkles and stretch marks.

Lines of CleavageLines of CleavageThe collagen and elastic fibers in

the dermis are usually arranged in parallel bundles◦Arranged to resist forces during

normal movement◦The pattern forms lines of cleavage

Lines of CleavageLines of CleavageWhy are the lines important?

◦Cuts parallel to the lines of cleavage will remain closed and heal with minimal scarring

◦Cuts perpendicular to the lines will be pulled open by the recoiling elastic fibers and will result in greater scarring.

THE SUBCUTANEOUS THE SUBCUTANEOUS LAYERLAYER

Integumentary System

The Subcutaneous LayerThe Subcutaneous LayerAlso known as the hypodermisConsists of areolar and adipose

tissue◦Very elastic

Superficial region contains blood vessels

Subcutaneous fat serves as an insulator and a major energy reserve for the body.

The Subcutaneous LayerThe Subcutaneous LayerAt puberty, distribution of fat

starts to differ between the sexes◦Men tend to store fat at the neck,

arms, low back, and buttocks◦Women tend to store fat at the

breasts, buttocks, hips and thighs◦Both can accumulate fat in the

abdominal region

ACCESSORY ACCESSORY STRUCTURESSTRUCTURES

Integumentary System

Hair and Hair FolliclesHair and Hair FolliclesHair – cover almost every surface

of your skin◦Exceptions are sides and soles of

feet, palms of hands, sides of toes and fingers, lips, portions of external genitalia

Body has 2.5 million hairs 75% NOT on your head

Hair is a nonliving structure produced by hair follicles◦Made of the protein keratin

Hair and Hair FolliclesHair and Hair FolliclesFunction of hair on head

◦Protect from UV radiation◦Cushion light blows to head◦Insulate skull

In nostrils and ear:◦Prevent entry of foreign particles

All hair serve as sensory receptors

Hair and Hair FolliclesHair and Hair FolliclesHave arrector pili muscles

attached to hair follicle◦When contracted, makes hair stand

up From emotions, cold (goose bumps) In furry mammals, this will increase

insulation, but doesn’t have that effect in humans

Hair and Hair FolliclesHair and Hair FolliclesHair will grow for 2-5 years

before being shed◦Grows about 0.33mm each day

While growing, the follicle will incorporate nutrients/chemicals into the hair shaft◦Can be useful for detecting disorders

or drugs.◦Can be used for DNA fingerprinting if

hair contains nucleated cells

Hair and Hair FolliclesHair and Hair FolliclesHair coloration is from the

melanocytes producing varying amounts of melanin in the hair follicle

Different forms of melanin will give hair a dark brown, yellow-brown, or red appearance

Glands In the SkinGlands In the SkinSebaceous (Oil) GlandsCan secrete oil from hair follicle

or directly onto skinThe secreted material is called

sebum◦Made of fatty acids, cholesterol,

proteins, and electrolytes◦Inhibits bacteria growth, lubricates

and protects hair, and conditions surrounding skin

Glands In the SkinGlands In the SkinSebaceous (Oil) Glands (Con’t)

◦Sebaceous follicles Glands NOT associated with hair follicles Discharge sebum directly onto epidermis Located on face, back, chest, nipples,

external genitalia Very active just before birth and during

puberty

Glands In the SkinGlands In the SkinSweat Glands

◦Also known as sudoriferous glands◦Two types

Apocrine sweat glands Found in armpits, around nipples, and pubic

region Secrete sweat into hair follicles Sticky, cloudy, odorous secretion Begin secreting at puberty This sweat is a nutrition source for bacteria,

which intensifies odor

Glands In the SkinGlands In the SkinSweat Glands (Con’t)

◦Two types Merocrine sweat glands

Discharge secretion directly onto surface of skin More numerous (2-5 million) than apocrine

glands Palms and soles have highest number

3000 per square inch Secretion is 99% water with some electrolytes

(mainly sodium chloride)

Glands In the SkinGlands In the Skin

NailsNailsProtect exposed dorsal surfaces of

the tips of the fingers and toesParts:

◦Nail body – visible portion of nail◦Nail bed – lies under nail body◦Lateral nail grooves – lateral borders of

nail body◦Lateral nail folds – portion of skin

overlapping lateral portion of nail body◦Free edge – distal portion extending past

nail bed

NailsNailsParts (con’t):

◦Hyponychium – thickened skin at distal end of nail bed

◦Nail root – forms the nail◦Eponychium (cuticle) – skin flap

covering proximal nail body◦Lunula – pale crescent at proximal end

of nail body

INJURY RESPONSEINJURY RESPONSEIntegumentary System

Injury ResponseInjury ResponseExcellent regeneration

capabilities and response to stresses.

Calluses form when repeated stresses from manual labor are placed on the skin◦The stem cells of stratum

germinativum divide more rapidly, thickening the skin in that area

Injury ResponseInjury ResponseThe process of injury repair can be

slow

Infection and fluid loss can complicate repair

The type of injury also determines rate of repair◦Thin, straight cut (incision) will generally

heal more quickly than a scrape (abrasion) because of the relative surfaces involved

Injury ResponseInjury ResponseBleeding occurs when the

damage extends into the dermis. Why?◦No vessels in epidermis

Injury ResponseInjury ResponseSteps to injury response

Step 1Bleeding occurs and mast cells

trigger the inflammatory response

Injury ResponseInjury Response

Step 2Blood clot (scab) forms

Restores integrity of epidermis Restricts microorganisms from entering area

Stratum germinativum cells migrate along edges of wound

Divide rapidly to replace epidermal cells

Macrophages patrol area collecting debris and pathogens

Injury ResponseInjury Response

Step 2 (con’t)Increased capillary formation

enhances blood flowCombination of blood clot,

fibroblasts, and new capillary network is called granulation tissue

Injury ResponseInjury Response

Step 3Over time, deeper portion of clot

dissolvesNumber of capillaries declineFibroblast activity leads to

increase in collagen fibers and ground substance

Epidermal cells have migrated over the network of collagen fibers

Injury ResponseInjury ResponseStep 4After several weeks, the scab is shedThe repairs do not restore the

integument to its original condition◦Dermis will contain abnormally large

numbers of collagen fibers, and few capillaries

Severely damaged hair follicles, glands, muscle and nerve cells are seldom repaired◦Replaced by fibrous tissue (Scar)

AGINGAGINGIntegumentary System

Aging and the IntegumentAging and the IntegumentEffects of aging on the integument

◦Thinning epidermis◦Decreased vitamin D production

Muscle and bone weakness

◦Decreased melanocyte activity More sensitive to sun

◦Decline in glandular activity Dry, scaly skin. Less perspiration means

increased overheating

◦Reduced blood supply to dermis

Aging and the IntegumentAging and the IntegumentEffects of aging on the integument

◦Hair follicles stop functioning Thinner, finer hair

◦Dermis thins Sagging and wrinkling occur

◦Decrease in sex hormones Hair characteristics and fat distribution change People of both sexes age 90-100 tend to look

alike◦Skin repairs more slowly

Repairs can take twice as long as a young adult

Recurring infections may result