biology 141 integumentary system chapter 5. the integument integument: skin – largest body organ ...
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Biology 141Integumentary SystemChapter 5
The IntegumentIntegument: Skin largest body organIntegumentary System:SkinHairNailsFunction:ProtectionMaintain body temperatureProvide sensory input
Dermatology: medical specialty dealing with the integumentary system
Structure of the SkinCutaneous membrane: skinEpidermis superficial layerDermis deep layer
Subcutaneous membraneHypodermis fat layer; not technically a part of the skin.
Structure of the SkinThe 2 layers of skin; epidermis Multilayered epithelial tissuethinner
EpidermisCell types found in the epidermis:Keratinocytes: multilayeredProduce keratin protein (tough, water repellant)MelanocytesProduces pigment melanin to protect nuclear DNA in keratinocytesLangerhans cellImmune responseMerkel cellsContact Merkle discs to detect sensations
Composed of different strata (layers)outermost - dead cells Innermost - Cells divideCells die as they are pushed upward Layers originate from the deepest cell layer of columnar cells called the stratum germinativum.
Sublayers of the Stratum germinativum
Stratum basale ("base layer") Cells of stratum basale are closest to the blood supply in the dermis and are thus the healthiest Only these cells can reproduce
Stratum spinosum ("spiny layer") Cells are pushed from below and become "squished" and look "spiny" on cross sectional view Because the cells are farther away from the dermal blood supply, they are less healthy and thus don't reproduce
Basal Cell CarcinomaLow magnification (left) of skin cross-section of shows different layers (epidermis, dermis and subcutaneous tissue), and areas of tumor invasion. Higher magnification (right): tumor cells resemble those in the normal basal cell layer of the epidermis. Tumor cells appear to bud off from the epidermis and grow downward as islands and cords of basophilic cells with hyperchromatic nuclei.
Epidermis Tissue Layers (deep to superficial)Stratum germinativum ("growth layer")stratum basal germination basement layerStratum spinosum thorn-like
Stratum granulosum "grainy layer"
Stratum lucidum "clear layer"
Stratum corneum horny layer (top layer)
Epidermis: Tissue Layersstratum basal: Single row of cuboidal or columnar keratinocytes.Some are stem cellsContainsMelanocytesLangerhans cellsMerkle cells and discs
Epidermis: Tissue Layersstratum basal Damage to this layer damages stem cellsUnable to regenerate skinRequire skin graftsGrafts can be autologous (same individual) or transplanted from a donor.Skin sheets can also be grown in the lab
Epidermis: Tissue Layersstratum spinosum multilayered keratinocytesFew Langerhans cells and Melanocytes
Epidermis: Tissue Layersstratum granulosumMultilayered, flattened keratinocytesCells undergoing apoptosisSecretes water repellantcells loose nuclei, appear grainy Keratohyalin (a precursor to keratin) forms in granules here
Epidermis: Tissue Layersstratum lucidum: Multilayered, dead keratinocyteswith large amount of keratin
Translucent and flattened
Found only in thick skin (hairless)FingertipsPalmssoles
Epidermis: Tissue Layersstratum corneum: MultilayeredFlat, dead keratinocytesprimarily keratin protein"horny layer" - cells have processes Flattened cells filled with keratin form "keratinized layer" and make this "keratinized stratified squamous epithelium"
Constant friction results in callus formation
DermisDermis: Connective tissueContainsBlood vesselsNervesGlandsHair follicles
Dermis2 main regions:
Papillary: upper layer
Reticular: deep layer
DermisPapillary: upper layerlies next to the epidermiscontains the derma papillae (projections into the upper epidermis) epidermal ridges creat fingerprints, palm prints and footprints.Contain capillariesContain Meisssner corpuscles (tactile receptors)Contain free nerve endingsSenses temperature, pain, itch, tickle
DermisReticular: deep layerAttaches to the subcutaneous layerDense irregular connective tissuecontains more collagen fibers increasing the strength of the skin.Contains:Few adipose cellsHair folliclesNerves and Pacinian corpuscles (deep pressure)Sebaceous glands (oil)Sudoriforous glands (sweat)
Accessory StructuresReceptors: Meissners corpuscles and Pacinian corpusclesMeissners: located in the papillary layer of dermisproject into the papillae.touch receptorsPacinian: spherical, onion-likeLie deep in the reticular layerpressure
Sensory receptors in the DermisMeissners Corpuscle detects light touchPapillary layerPacinian Corpuscle detects deep touch (pressure)Reticular layer
DermisTears in the reticular region of the dermis result in stretch marks.
Incisions against the grain of the collagen fibers = wide scar
Incisions with the grain = thin scar
Structural Basis of Skin ColorSkin color pigments:MelaninHemoglobinCarotene
Melanin number of melanocytes the same in all peopleAmount of melanin produced variesAccumulation results inAge spotsFrecklesmoles
MelaninFunction:Absorbs UV radiationPrevents damage to DNA in epidermal cellsNeutralizes free radicals
HemoglobinFound in RBCs
Skin color depends on amount of oxygen in the blood Blue cyanotic: low oxygenYellow - jaundice: high bilirubinLiver damageRed erythema: engorgement of capillariesInjuryHeatInfectionInflammationAllergic reactionWhite pallor: low number of RBC Shockanemia
CaroteneYellow-orange pigment found in egg yolks and orange vegetablesPrecursor to vitamin AExcessive dietary intake results in accumulation in the subcutaneous layer
Albinism / VitiligoAlbinism: Inherited inability to synthesize melaninMelanin is not produced in skin, hair, and eyes.
Vitiligo: partial or complete loss of melanocytes in patches of skinImmune system attacks and destroys melanocytes.
Accessory StructuresHair: piliColumns of dead, keratinized cells - compactly cemented together.hair shaft portion of the hair that projects above the surface.root portion below the surface extending into the dermis.
HairHair shaft and root consist of 3 concentric layers of cells:MedullaCortexCuticle
Human HairCuticle showing scalesNo medulla, brown pigment granules in cortexLight medulla
HairHair follicle: composed of the root sheath encasement with 2 layers:Internal root sheath produced by matrix, surrounds rootExternal root sheathextension of epidermisThe Dermal root sheath is part of the dermis
Hairbulb - enlarged region of the root containing the follicular papilla (involution of loose connective tissue).
Hairarrector pili muscle smooth muscle that upon contraction forces the skin into goose bumps.
Accessory StructuresGlands: sebaceous and sweat glands
Sebaceous glands:Usually connected to hair folliclessecretes sebum (oil)Moisturizes hair and skinkeeps hair pliable.Keeps skin softInhibits bacteria
Acne: Inflammation of a sebaceous gland.
Blocked sebaceous glandNormal sebaceous gland
Sudoriferous Glands (Sweat glands)2 main types of glands: eccrine and apocrineeccrine: empty directly out through the skin surfacetubular with a coiled basal portion located deep in the dermisRegulates body temperatureapocrine: larger, empty directly into the hair follicle canalsecretory portion located in the subcutaneous layerExcretory duct opens into hair folliclestimuli: psychic factors; emotions, sexual excitement
Accessory structures and location
Ceruminous GlandsModified sweat glands in the external ear.Produce ear wax (cerumen)Provides a sticky barrier
NailsTightly packed, hard, keratinized epithelial cells.
Structure:Nail body: visible portionPink due to capillary bedFree edge: part that extends past the digitWhite due to lack of capillariesNail root: portion buried in a fold of skin
Types of Skin2 types of skin based on structure:Thin (hairy) skinThick (hairless skin)
Functions of the SkinThermoregulation: by sweat and blood flowBlood reservoir8-10% of blood flowProtectionAgainst external assaultCutaneous sensationsTactile, pressure, pain, temperature, tickleExcretion and absorptionExcrete salts, water, and small amounts of CO2 and ureaAbsorbs lipid molecules (vitamins A,D,E and K, drugs, lotions, poisons, heavy metals, steroids)Synthesis of vitamin DUV light activates precursor molecules that can be modified by the liver. Vit. D produces calcitrol which aids in the absorption of calcium in the GI tract.
Maintaining Homeostasis: Skin Wound HealingWound healing can occur via 2 routes:Epidermal Wound Healing affects only the epidermis.
Deep Wound Healing wound extends to dermis and subcutaneous layers
Epidermal Wound HealingInjury response:Basal cells detach from the basement membrane.Hormone (epidermal growth factor) stimulates basal stem cells to divide to replace migrating cells.Migrating cells move across woundCells stop migrating upon touching other cells (contact inhibition)
Deep Wound Healing
4 phases:Inflammatory: clot formation closes the wound, WBC kill invadersMigratory:scab formation, epithelial cells migrate, fibroblasts produce fibrin for scar tissueProliferative:Extensive growth of epithelial cells, depositing collagen fibersMaturation:Scab sloughs off, collagen fibers organize
Development of the Integumentary SystemEpidermis is derived from the ectodermDermis is derived from the mesoderm
Aging and the Integumentary SystemMost changes occur in the dermisCollagen fibers decrease in numberElastic fibers loose elasticityFibroblast (produce collagen and elastin) decrease in numberDecrease number of melanocytes gray hairSubcutaneous adipose tissue is lostHealing is longer
Sun DamageUV A rays:Not absorbed by the ozone layerPenetrate deep into skin and absorbed by melanocytesDepress the immune systemDarken the skinUV B rays:Some absorbed by ozonePenetration of skin not as deepCause sunburn
Sun DamageSunscreenAbsorb UV B, but allow UV A rays to reach the skinSunblockBlock both UV A and UV B rays
Skin CancerBasal cell carcinoma78% of all skin cancersTumors arise from the stratum basaleRarely metastasizeSquamous cell carcinoma20% of all skin cancersArise from squamous cell of epidermismetastasizeMalignant melanoma2% of all skin cancersArise from melanocytesMetastasize rapidly (can kill within months)
Skin CancerBasal cell carcinomamelanomasquamous cell carcinoma
BurnsBurns are graded by severity:First degree: only epidermis, redSecond degree: all epidermis and part of dermis, blistersThird degree: all epidermis, dermis and subcutaneous layers, blackFourth degree: muscle layers are burned
BurnsHalf of all patients with over 70% of the body burned, dies.
Estimating surface area for burns uses the rule of nines.
BurnsHead and neck (front and back)9% Each upper limb (front and back)9% Trunk (front and back)4 x 9% (or 36%)Each lower limb 9% front9% back
Perineum (anal and urogenital region)1%
Pressure UlcersDecubitus ulcers caused by constant deficiency of blood flow from prolonged pressure against an object.
Occur most often in bedridden patients.