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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