Two Divisions of the Integumentary System1. Skin=integument=cutaneous membraneSkins is the largest organ of the body—surface area of 1.2 to 2.2 square meters; weighs 9 to 11 pounds (4-5kg)=7% of the total body weightComposed of the superficial epidermis and the deeper dermis2. Accessory skin structures=skin appendagesi) Sweat (Sudoriferous) glandsii) Sebaceous (oil) glandsiii) Hair/hair folliclesiv) NailsStrata of the EpidermisStratum Basale—deepest stratumStratum Spinosum—contains tonofilamentsStratum Granulosum—contains granulesStratum Lucidum—present only in thick skinStratum Corneum—superficial stratumStratum BasaleThe deepest stratumA single layer of cells including keratinocytes, melanocytes, Merkel cells:Keratinocytes are mitotically active producing cells for the superficial layers hence, the stratum basale is also known as the stratum germinativumMelanocytes produce the pigment melanin contained in melanosomes—melanosomes accumulate on the superficial surface of the keratonocytes in the stratum basale; melanin acts as a chemical shield to protect the nuclei of the keratinocytes from the harmful effects of UV radiation in sunlight; melanin gives skin its color; albinism- genetic condition in which melanin is not synthesizedWhen you go out into the sun, these cells make extra melanin to protect you from getting burned by the sun’s ultraviolet, or UV rays=tanningMerkel cells at the epidermal-dermal junction associate with free nerve endings to form Merkel Discs which act as touch receptorsStratum SpinosumSeveral layers of cellsCells are connected by desmosomes—hold cells together which cause the cells to appear “spiny” during histological preparationCells contain intermediate filaments called tonofilamentsEpidermal dendritic cells—Langerhans’ cells in the stratum spinosum act as macrophages to engulf and digest pathogensStratum GranulosumComposed of 3-5 layers of cellsCells contain two types of granules:Lamellated granules- contain glycolipids—the lipids that make the epidermis water-proofKeratohyaline granules- contain the tough, insoluble protein, keratin, which makes the epidermis tough and abrasive-resistantStratum LucidumThin, translucent layer of deal cellsThickens the epidermisPresent only in thick skins—palms, solesStratum CorneumSuperficial layer of the epidermisComposed of 20-30 layers of dead, flat cellsDeal cells are impregnated with glycolipids and keratin to provide a tough, durable, water-proof “coat”Replaced every 3-4 weeksThe DermisConsists of the superficial papillary layer and the deep reticular layerThe papillary layerComposed of areolar connective tissueSurface has peg-like projections called dermal papillae—house blood capillaries and nerve endings and Meissner’s corpuscles which act as touch receptorsIn thick skin, the surface of the papillae are supported by mounds called Dermal Ridges which form impressions on the epidermal surface called the epidermal ridges (friction ridges)—increased friction and enhance grippingPattern of epidermal ridges is genetically determined and therefore unique to an indivudual—acts a the basis for finger-printingReticular Layer of the DermisDeeper layer accounting for 80% of the dermisComposed of dense irregular connect tissueContains the touch receptors for deep pressure called Pacinian corpusclesCleavage (tension) lines—areas of the reticular layer with less collagen bundlesIncisions made parallel to the cleavage lines gape less and therefore heal fasterStriae (stretch marks)—indicate dermal tearing replaced by slivery white scarsLocation of the Nervous Structures in the SkinMerkel discs: epidermal-dermal junctions; act as light touchMeissner’s Corpuscles: papillary layer of the dermis; act as touch receptorsRoot hair plexus: wrapped around the base of a hair follicle called the hair bulb and it is stimulated when the hairs bend; act as touchPacinian Corpuscles: located in the reticular layer of the dermis and they respond to deep pressure placed on the skinAccessory Structures of the SkinAll derived from the epidermis but reside in the dermis:Sweat (Sudoriferous) glandsSebaceous (oil) glandsHairs/hair folliclesNailSweat GlandsSuderiferous glandsSimple coiled tubular multicellular exocrine glandsTwo types: Eccrine and ApocrineEccrine Sweat Glands:Three million per personAbundant in the palms, soles, and foreheadSecrete sweatUse the merocrine mode of secretionHence, the eccrine sweat glands are also known as merocrine sweat glandsComposition of SweatHypotonic filtrate of blood99% waterAntibodiesVitamic CSalts—NaClMetabolic wastesDermicidin—antimicrobial proteinpH between 4-6=acidicAcidic mantle—acidic pH of sweat prevents microbial growth on the surface of the skinApocrine Sweat Glands2000 of them located in the anogenital and axillary (armpits) areasBecome active after puberty when they are stimulated by the sex steroid hormonesSecrete a viscous, yellowish fluid onto hair folliclesSecrete their product via merocrine mode of secretionSecretion is associated with body odor hence, the apocrine sweat glands are also known as “odoriferous” glandsTwo Specialized Sweat GlandsCeruminous glands- specialized sweat glands located in the lining of the external ear canal; they secrete a bitter substance called cerumen (earwax) which prevents entry of foreign objects such as, insects and water, into the earMammary glands- specialized sweat glands located in breasts; secrete milk to feed the youngSebaceous GlandsOil glandsSimple alveolar glandsFound all over the body except the palms/solesSecrete an oily substance called sebum into hair follicles and via pores to the surface of the skinSebum softens and lubricates hair and skinSecrete via the holocrine mode of secretionWhiteheads- sebum accumulated in the ducts of the sebaceous glandsBlackheads- popped whiteheads that result in oxidation and darkeningAcne- inflammation of sebaceous glands caused by bacteriaHairs=PiliProduced by cells in the matrix inside hair folliclesEach hair has two regions—shaft and rootShaft- region exposed above the skinRoot- region below the skin enclosed by the hair follicleThree Concentric Layers of HairHair is composed of three concentric layers of keratinized cells:Inner medulla—the coreMiddle cortex—the largest layerOuter cuticle—a single layer of overlapping cells that protects the underlying layers and to prevent hair from mattingConditioners keep the cuticle smooth to prevent matting
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