the integumentary system - kdmassey.orgkdmassey.org/student/anatomy and...

The Integumentary System

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Integumentary System - General

Skin & its derivatives (sweat glands, oil glands, hair & nails)Skin is largest organ (7% of body by wt.), 1.5 - 4 mm. thickFlexion (flexure) creases – on surface where skin folds during movement (palmar surface)

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Integumentary System - General

Flexion lines – on surface where skin stretches during movement (elbow)2 Major regions of skin:

Epidermis – superficial, stratified squamous epitheliumDermis – dense irregular C.T.

Skin sits upon hypodermis (superficial fascia, or subcutaneous) – loose C.T.

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Epidermis

EctodermalUsually < 0.12 mm thick

Thicker at friction sitesKeratinocytes – most abundant cell type

Derived from deepest part of epidermis by mitosis & cytokinesisProduce keratinInterconnected by desmosomes

Other cells present

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Epidermis, Cont.’d

Melanocytes – in deepest layerProduce melanin – a yellow to reddish-brown to black pigment

Pigment produced from tyrosine (an amino acid)Accumulates in melanosomes within melanocyte

Accumulate in processes for transfer to keratinocytesCollects on “sunny” side of keratinocyte nucleus …shields nucleus DNA from UV

Langerhans’ cells – activate the immune system From bone marrow, cells possess slender processes

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Epidermis, Cont.’d

Merkel cells – at epidermal-dermal junction

Associated with disc like sensory nerve endingMerkel disc = Merkel cell + nerve ending

Function: touch receptor

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Epidermal layers – Thick Skin

5 layers (strata) –palms, fingertips, soles of feet:

1 Stratum basale (S. germinativum)Deepest, usually a single row of cellsYoungest keratinocytes + 10-25% melanocytes.Site of mitosis & cytokinesisMay contain Merkel cells

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2 Stratum spinosum – 8-10 cell layersCells may appear flattened & spinyMainly keratinocytes with melanin granules & Langerhans’ cells

3 Stratum granulosum – 3-5 cell layersCells more flattenedNuclei & organelles begin to disintegrate (distance from blood vessels)Accumulate a gummy keratohyaline granules & lamellated granules (contain waterproofing glycolipid)

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4 Stratum lucidum – 3-4 layers of clear dead cells

Only found in thick skinKeratohyaline granules begin to cling to keratin filaments parallel bundled arrays of keratin filaments

5 Stratum corneum – 15-30 layers of dead cells

Keratin & thickened P.M. prevent abrasion & penetration, glycolipid waterproofs

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Epidermal layers

Shingle-like cells called cornified cells

Thin skin – Covers most of bodyStratum lucidum absent & other strata may be thinner

Rete pegs – The projections of the epidermis extending between upward projections of dermis (papillary pegs)

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Dermis – Averages 2 mm. thick

Deeper region of skinVascularContains sensory receptors and nerve fibersContains glandsContains major portion of hair follicles

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Dermis – 2 layers

Papillary layer – thin & superficial 1/5 Loose c. t.Papillary pegs (dermal papillae)

May contain capillary loops, free nerve endings (pain receptors), & Meissner’s corpuscles (touch receptors)

Dermal ridges on palms & solesElevate overlying epidermis to form epidermal ridges …fingerprints

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Dermis – 2 layers

Reticular layer – deep 4/5 of dermisDense irregular c.t.

Separations or less dense regions called cleavage lines

On limbs…longitudinal, on trunk…circularSignificance ………

Striae (stretch marks) – dermal tearingBlister – separation of epidermis from dermis (from burn or other trauma)

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Skin Color

Melanin – skin coloration reflects the relative kind and amount produced

In humans melanocyte number is same in same region of bodyLocal accumulations: freckles, pig. MolesTan – skin darkening with local accumulation, due to UV exposureExcessive sun: leathery skin, skin cancer, premature aging of skin, depresses immunity

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Skin Color

Photosensitivity – increased skin sensitivity to UV

Antibiotics, perfumes, detergents, other chemicalsBlisterlike lesions and skin peeling

Carotene – yellow to orange pigmentProduced by plantsAccumulates in S. corneum & hypodermis

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Skin Color

Degree of oxygenation of hemoglobinCyanosis - blue appearing skin

Mucous membranes & nail bedsErythema (redness) – blushing(b.v. diameter), fever, hypertension, polycythemia, inflammation or allergyPallor (blanching) – emotional stress (fear, anger) or anemia

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Skin Color

Bronzing – Addison’s diseaseHypofunction of adrenal cortex

Jaundice – liver disorder or excess RBC destruction

Excess bilirubin, a bile pigmentHematomas – black & blue marks where blood has clotted below the skinVitiligo – patches of white skin at sites of melanocyte destruction (autoimmunity –1%)

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Appendages of the skin

Sweat glands (sudoriferous glands)Absent from lips Eccrine – merocrine, general distribution

Simple coiled tubular gland, pore at skin surfaceSweat released by exocytosis, it contains:

99% H2O, NaCl, vitamin C, antibodies, wastes (urea, ammonia, uric acid), lactic acid & some drugspH = 4-6Prevents overheating

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Apocrine – anal, genital, axillary, & areola & nipple

Duct opens into hair follicle, myoepithelial cellsSweat same as eccrine plus fatty substances and proteins present …body odorDevelop at puberty in response to androgensRespond to emotional stress, pain, sexual foreplay, not temperature

Ceruminous glands – produce cerumin (earwax) in external ear canal

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Mammary gland – secrete milkSebaceous gland – sebum (oil) product

Holocrine, hormone stimulationUsually develop from & secrete into hair follicleUsually simple, sometimes branched alveolarAbsent from palmar & plantar surfaces

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Whitehead – sebum blocked sebaceous gl. duct

Blackhead – oxidized & dried sebumAcne – an active inflammation of sebaceous gland with skin eruption

Proprionibacterium acnesSeborrhea –common skin condition with overproduction of sebum

Ex.: Cradle cap of infants – washing to remove excessive oils

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Hairs & Hair Follicles

Absent from palms, soles, lips, nipples, & parts of ext. genitaliaScalp hair guards against physical trauma, heat loss & sunlightEyelashes shield eyes

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Structure of a hair:

Columns of dead keratinized cells produced in a hair follicle

Hard keratin – more durable, cells less likely to flake

2 regions of hair:Shaft – visible portion projecting from skin

Flat…kinky, oval…silky & wavy, round…straight & coarse

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Root – part embedded in skin3 concentric layers of hair(c.s.):

Medulla – central coreAbsent from fine hairsLarge cells & air spaces

Cortex – surrounds medullaSeveral layers, receives pigment from melanocytes at the base of hair follicle

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Cuticle – single layer of overlapping cellsProvides strength and compaction“split ends” – when cuticle wears awayHair color – various proportions of melanins

Red hair – iron-containing melanin (trichosiderin)Gray hair – decreased melanin production & air bubbles in medulla

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Structure of hair follicle:

Bulb – the expanded base of follicleContains the hair papilla

Indentation containing loose c.t. & blood vessels

Concentric hair follicle regions:Connective tissue sheath (outer)Glassy membrane (b.m. of next region)External root sheath – epithelial

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Structure of hair follicle:

Internal root sheath – epithelialDoes not extend superficially past sebaceous gland duct3 single-celled layers (Henle’s, Huxley’s & cuticle layer of inner root sheath)Narrows more deeply to single layer, the hair matrix

Actively carry on mitosis & cytokinesisHair matrix cells originate & migrate from a slightly more superficial region, the hair bulge

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Arrector pili

Bundle of smooth muscle running diagonally from c.t. sheath at base of follicle to papillary layer of dermisContraction erection of hair (goosepimples)Increases sebum secretion, other??

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Types of hair

Vellus hair – a pale, fine hair varietyBody hair of children & adult females

Terminal hair – coarser, longer, often darker hair of eyebrows, scalp, and after puberty axillary & pubic regions

Grow in response to androgens, such as testosterone

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Growth of terminal hair

Influenced by nutrition & hormonesPoor nutrition…poor hair growthIncreased blood flow…enhance hair growthLarge amount of testosterone…luxuriant hair growth

Removal of unwanted hair by electrolysis & laser treatments

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Growth of terminal hair, Cont.’d

Alternate grow state & resting stageResting stage – hair matrix inactive & hair base and bulb atrophiesEye lashes – grow 30 days, rest 105 daysScalp hair – averages 4 year growth, rests a few months

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Hair Thinning & Baldness

After 40’s hair growth slowsThinning and some degree of baldness (alopecia) in both sexes

Usually begins at ant. hair lineTerminal hairs replaced by villus hairs

Male pattern baldnessSex-influenced conditionGene switches on in adulthood & changes response to testosterone

Growth cycle shortens with replacement by villus hair Minoxidil (high B.P. treat.) & life-long finasteride

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Hair Thinning & Baldness

Hair thinning induced by:High fever, surgery, severe emotional trauma, excess Vit. A, some antidepressants & chemotherapy drugsProtein deficient diets

Inadequate protein for keratin synthesisLactation

Protein used for milk production, temporary

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Nails

Plates of tightly packed, hard, keratinized epidermal cells over dorsal distal portions of finger & toes Picking up small objects & scratchingParts: Free edge, body & rootNail bed – surface to which nail body root are attached

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Nails

Nail matrix – thickened proximal portion of nail bed (stratum germinativum)

Responsible for nail growthLunula – small portion of nail matrix visible through nail body, crescent shape

Because of thickness – appears white

Eponychium (cuticle) – stratum corneum that occupies the proximal border of nail

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Nails, Cont.’d

Hyponychium – thickened layer of stratum corneum below free edge of nailNail folds: proximal, lateral & medial

Skin folds overlapping borders of nail

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Functions of the Integumentary System:

Chemical barrier –secretions & melaninAcid mantle (low pH) retards bacterial growthSebum may kill some bacteriaHuman defensin – natural antibioticMelanin helps prevent UV damage

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Physical (mechanical barrier):Due to continuity of skin & hardness of keratin…bacterial barrierGlycolipids from lamellated granules –prevent the loss from and entry intobody through the skin of H2O & H2O soluble substances

Not blocked are fat soluble : O2, CO2, fat soluble vitamins (A, D, E, K), & steroids

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Not blocked plant resins : of poison ivy & poison sumacNot blocked organic solvents : acetone, dry cleaner solvent, paint thinner (they dissolve cell lipids) – kidney failure, brain damageNot blocked salts of heavy metals : lead (Pb), mercury (Hg), nickel (Ni)

Pb – anemia & neurological defectsNot blocked penetration enhancing drugs : dialkylamino acetates

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Biological barriers :Langerhans’ Cells of epidermis & macrophage cells of dermis : phagocytize & present antigen to cells of immune system (T-lymphocytes) –activate immune systemMacrophages of dermis –directly phagocytize & destroy some attackers

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Body temperature regulation : Cooling factors (heat loss center*):

Sweat glandsDilation of dermal vessels

Warming factors (heat gain center*) :Constriction of dermal vesselsContraction of skeletal muscles

*located in hypothalamusof brain

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Cutaneous sensation :Meissner’s corpuscles – light touch (clothing)Merkel discs – samePacinian corpuscles – heavy pressureRoot hair plexuses – bending of hairFree nerve endings – painHeat & cold receptors

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Production of Vitamin D :

7-dehydrocholesterolVit. D3

(Cholecalciferol)

-liver-kidney

Calcitriol

Increased Intestinal absorption of Ca++ + PO4

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UVlight

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Keratinocytes:Convert topically applied cortisone to hydrocortisone (anti-inflammatory)Produce hormone that stimulates T-cellsDisarm some cancer causing chemicals

Skin cells :produce collagenase for collagen fiber turn-over (deters wrinkling)

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Blood reservoirCan hold up to 5% of blood volumeConstriction of dermal vessels diverts blood to “needy site”

Excretion of ammonia, urea, uric acid, some medications, NaCl, excess H2O

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Skin Cancer

Tumors (neoplasms) can be benign or malignant

Most benign – ex.: wartRisk factors:

UV of sunlight – disables tumor suppressor gene (p53) or patched gene (ptc)Frequent irritation: infection, chemicals, traumafas protein – reduces risk in sunburned skin by skin suicide method & peeling of skin

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Skin Cancer

Basal cell carcinoma – 75% of skin cancers, least likely to spread, stratum basale proliferates

Invades dermis & hypodermis, slow growingShiny dome shaped, develop a central ulcer with pearly beaded edge99% curable by surgery

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Skin Cancer

Squamous Cell Carcinoma – about 20%Scaly reddened papule (small rounded elevation) Most often on head (scalp, ears, lower lip) and handsGrows rapidly & metastasizesSurgical removal &/or radiation, if early good results

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Skin Cancer

Melanoma – about 5%Wherever melanin present, 1/3 from molesSpreading brown to black patchMetastasizes rapidly to surrounding lymph & blood vesselsChance of survival if over 4 mm. thick is poorWide surgical incision & immunotherapy

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Skin Cancer

ABCD(E) Rule (American Cancer Society) for melanoma

Asymmetry – 2 sides do not matchBorder – exhibits indentationsColor – contains several colors (black, brown, tan, blue, red)Diameter – 6 mm. or more diameter (pencil eraser)Elevation

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Burns

Loss of tissue fluid & plasmaDehydration, kidney damage, shock, infectionDegree:

1st : Only epidermal layers damagedPain, redness, swelling (as in mild sunburn)

2nd : Damage of epidermis & some dermisBlisters (vesicles)

3rd : No epidermis at site, extends subdermally

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Burns, Cont.’d

May call for graftingSplit skin grafting – epidermis & ½ of dermisArtificial skin grafts – silicone(epid.) + collagen & cartilage(dermis), + cultured patient’s cellsRule of nines – estimating burn extent

H 9, SL9, Trunk36, IL18, Genetalia1

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Clinical Terms:

Boils -Milia- small white spotsCarbuncles on forehead & noseCold soresDecubitus ulcer (bedsore)DermatologyImpetigoVernix caseosa – white cheesy sebum of newborn

the integumentary system - kdmassey.orgkdmassey.org/student/anatomy and...

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