BIO 210 LabInstructor: Dr. Rebecca Clarke

Chapter 5:The Integumentary System

Parts of the Integumentary SystemCutaneous membrane (integument,

skin)(outer) epidermis = superficial epithelium(inner) dermis = underlying area of

connective tissuesAccessory structures – located primarily

in dermis, protrude through epidermis to skin surfaceHairNails(Multicellular) exocrine glands

AlsoBlood vessels throughout dermisSensory receptors – monitor touch,

pressure, temperature, pain

Integumentary System

Cutaneous membrane = epidermis + dermis

Figure 5–1

Layers (Strata) of EpidermisFrom basal lamina to free surface:

stratum germinativumstratum spinosumstratum granulosumstratum lucidumstratum corneum

Stratum Germinativum (Basale)Single layer of basal (germinative, stem)

cellsSite of cell division; replenishes epidermis

Attached to basal lamina by hemidesmosomes

Forms strong bond between epidermis and dermis

Stratum GerminativumForms epidermal ridges (Fig 5-2)

fingerlike projections into dermis underneath; intermesh with dermal papillae

ridge-shaped pattern (fingerprint) on surface of skin which is unique for each individual (genetically determined) (Fig 5-4)

increase strength and bond between epidermis and dermis

Has melanocytes (with melanin pigment) – give skin its color (Fig 5-5)

Organization of the Epidermis

Figure 5–2

Ridges and Ducts

Figure 5–4

Stratum Spinosum“Spiny layer”

cells shrink until cytoskeletons stick out (spiny)

8-10 cell layers of keratinocytesDividing cells from stratum

germinativum push up through this layerStill some cell division

Stratum Granulosum“Grainy layer”3-5 cell layers thick Cells stop dividing, start producing proteins

grainy appearancekeratin:

tough, fibrous protein makes up hair and nails water resistant, not waterproof

keratohyalin dense granulescross-link keratin fibers tightly interlocked cell layers

Cellsthinner, flatter, less permeablefurther from papillary plexus, start to die

Stratum Lucidum“Clear layer”Cells flattened, densely packed, filled with

keratin barrier to waterOnly in thick skin (on palms and soles)

Stratum Corneum“Horn/hard layer” on exposed surface of skin15-30 cell layers of dead cells (far from

nutrients in dermis); durable, expendable protective function

Cells filled with keratin (= keratinized) water-resistance (not waterproof)

Cells tightly interconnected by desmosomes so are sloughed off in sheets

Cells remain for 2 weeks (total of 6 weeks from origin in stratum germinativum to sloughing)

2 Kinds of SkinThin skin

Has 4 layers of keratinocytes (missing stratum lucidum)

Covers most of bodyThick skin

Has all 5 layers of keratinocytesCovers heavily abraded body surfaces, e.g.,

palms of hands, soles of feet

DermisLocated between epidermis and

subcutaneous layerContains

Blood and lymph vesselsNerve fibers and sensory receptors

Tactile (Meissner’s) corpuscles – sensitive to light touch; located in dermal papilla

Lamellated (Pacinian) corpuscles – sensitive to deep pressure and vibration

Accessory organs (of epidermal origin), e.g., hair follicles, sweat glands

Components of Dermis2 major components – boundaries

indistinctPapillary layerReticular layer

Associated structuresPapillary plexus = branching network of

small arteries in papillary layer of dermis which provide blood to capillary loops that follow contours of epidermis-dermis boundary

Papillary LayerHas dermal papillae projecting between

epidermal ridgesConsists of areolar tissueContains smaller capillaries, lymphatics,

and sensory neurons

Reticular LayerDeep to papillary layerConsists of dense irregular connective

tissueContains

Larger blood vessels, lymph vessels, and nerve fibers

Collagen and elastic fibers Strength and elasticityFlexibility

Dermatitis An inflammation of the papillary layerCaused by infection, radiation, mechanical

irritation, or chemicals (e.g., poison ivy)Characterized by itch or pain

Subcutaneous Layeraka hypodermis (“below dermis”),

superficial fasciaHighly vascularized – contains large

arteries and veins; site of subcu injections

Separates integument from deep fascia around other organs, e.g., muscles and bones

Stabilizes position of skin relative to underlying tissues, e.g., skeletal muscles or other organs, while permitting independent movement

Structure of Subcutaneous LayerConsists of

Elastic areolar (loose) connective tissueAdipose tissue (energy reserve, shock

absorber)

Accessory Structures of the Integumentary SystemDerived from epidermisLocated in dermisExtend through epidermis to skin surfaceInclude:

Hair follicles and hairsExocrine glandsNails

Structure of a Hair and Follicle

Figure 5–10a

Hair FolliclesLiving organsProduce “nonliving” hairs; complex process

involving dermis and epidermisExtend deep into/through dermis and into

underlying subcutaneous layerWrapped in dense connective tissue sheath

of dermis

Follicle WallComposed of epithelial cellsCells organized into 3 concentric layers

(from outside in)Glassy membrane:

Thickened basal laminaExternal root sheath:

Widest layerInternal root sheath:

Contacts cuticle (outer layer of hair)

Structure of a Hair and Follicle

Figure 5–10

Structure of a Hair FollicleHair bulb

Bulbous mass of epithelial cellsHair matrix

Layer of epithelial cells in central, deepest part of follicle

Site where cell division begins that produces hairCells gradually pushed toward surface as hair gets

longerHair papilla

At base of follicle (below matrix)“Peg” of connective tissue that contains capillaries

and nervesIf damaged, hair will not grow

Structure of a Hair and Follicle

Figure 5–10

Hair StructureHair root

Lower part of hairBegins at base of hair (bulb) and extends

about halfway to skin surfaceAnchors hair into skin;

Hair shaftUpper part of hairExtends from above the root to above the

skin surface

Structure of a Hair and Follicle

Figure 5–10

Layers Within HairCuticle

Outer surfaceLayer of overlapping, dead keratinized cellsContains hard keratin hair stiffness

CortexIntermediate layer below cuticleAlso contains hard keratin

MedullaMiddle layer, central coreContains soft keratinFlexible

Structure of a Hair and Follicle

Figure 5–10

Associated StructuresArrector pili muscle

Involuntary smooth muscleContractions cause hairs to stand up

“goose bumps”

Exocrine GlandsSebaceous (oil) glands:

holocrine glandssecrete sebum

Sweat (sudoriferous) glands:merocrine glandsapocrine glands

Types of Sweat GlandsApocrine:

Associated with hair folliclesFound in armpits, around nipples, and groin

Merocrine:Widely distributed on body surfaceEspecially on palms and soles

Merocrine Sweat GlandsAlso called eccrine glandsSmaller but more numerousCoiled, tubular glandsWatery secretion = sensible perspiration

(produced by glands) vs. insensible perspiration which is the loss of fluid by evaporation through the stratum corneum

NailsNonliving structures; made of dead cells

packed with keratinForm on dorsal surface of tips of fingers

and toesFunction = protect fingers and toesMetabolic disorders can change nail

structure, e.g., shape, appearance; can assist in diagnosis

Nail StructureNail body - Superficial, visible portionNail bed – area of epidermis under nail bodyNail root – epidermal fold not visible from

surface; where nail production occursEponychium – extends over exposed nail

forming cuticleHyponychium – skin beneath free edge of nailLunula (“moons”) pale crescent at base of nail

where underlying blood vessels may be obscured

Structure of a Nail

Figure 5–13