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Two Functions of the Barrier System
- -Protection from Microorganisms and UV light
- -Relatively permeable to water (prevents evaporation of body fluids)
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Definition of Sensation
Highly innervated with lots of receptors
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Definition of Thermoregulation
Sweat glands, vasodilation
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Definition of plasticity/elasticity
Allows for changes in size and shape
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3 Layers of skin
- -Epidermis
- -Dermis
- -Hypodermis (subcutaneous tissue)
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Characteristics of Thick Skin
- -400-600 μm (thickness)
- -Hairless
- -Location: Soles of feet and palms
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Characteritics of Thin Skin
- -75-100 μm
- -Hairy
- -Location: Everywhere else
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5 Layers of Epidermis
- -Stratum Basale
- -Stratum Spinosum
- -Stratum Granulosum
- -Stratum Lucidum
- -Stratum Corneum
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Function of Stratum Basale
- -Single layer of cuboidal cells sitting on basement membrane that undergo intense mitotic division
- -Renewed about every 15-30 days
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Describe Stratum Spinosum
- -"spiny cells"; cuboidal cells like stratum basale
- -Filled with keratin filaments that are anchored into desmosomes
- -Desomosomes firmly bind cells of this layer together
- -Function: resist abrasion
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Describe Stratum Granulosum
- -3-5 layers of squamos cells; cytoplasm filled with vesicles
- -Vesicles fuse with the cell membrane and discharge contents into the intercellular space
- -Secreted material contains high concentration of lipid molecules
- -Function: Provides an intercellular cement. Creates a barrier to foreign materials
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Define Stratum Lucidum
- -Most apparent in thick skin; minimal layer in thin skin
- -Translucent layer of squamos cells with no apparent organelles
- -Densely packed keratin filaments anchored to desmosomes (provide strength to this layer)
- -Function: Resist abrasion
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Describe Stratum Corneum
- -Outermost surface of skin
- -15-20 layers of flattened non-nucleated cells; cytoplasm filled with keratin (i.e. "keratinized")
- -Cells consist of only keratin fibers, proteins and thick cell membranes (no organelles; lifeless cells)
- -Cells of this layer are continuously shed; termed "desquamation"
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Properties of Keratinocytes
- -Generic term
- -Epithelial cell in any & all layers
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Properties of Melanocytes
- -Produce melanin
- -Found in basal layer
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Langerhans' cells
- -Skin macrophages
- -Inner layer of epidermis
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Properties of Melanocytes
- -Location: Between stratum basale and spinosum
- -Synthesize melanin (dark pigment protects from UV radiation)
- -Melanin is transferred to keratinocytes at deep layers of skin and deposited "on top" of cell nuclei
- -Highest concentration of melanin occurs in cells in deeper layers of skin
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Facts about Langerhan's cells
- -Resident "macrophage-like" cells of skin
- -Found in stratum basale and stratum spinosum
- -Represent approx. 2-8% of epiermal cells
- -Bone marrow derived; carried to the epidermis via the blood
- -Can bind and present antigen to lymphocytes for immune functions against micro-organisms
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Components of Dermis
- -Loose CT (papillary layer) and dense irregular CT (reticular layer)
- -Neuronal innervation (skin sensory receptors)
- -Blood vessels are abundant in the dermis
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Skin appendages of Dermis
- -Hair follicles, nails
- -Sebaceous glands, sweat glands
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Facts about Subcutaneous Layer
- -Loose CT that binds skin to underlying structures (hypodermis, superficial fascia)
- -Often contains numerous fat cells
- -Also contains neurovascular networks
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3 Types of Epithelial glands
- -Holocrine
- -Merocrine
- -Apocrine
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Holocrine gland
-Secretory product is released along with the entire contens of the cell
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Merocrine (eccrine) gland
-Secretory product is released through exocytosis
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Apocrine gland
-Secretory product is released with portion of cellular cytoplasm
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Facts about sebaceous glands
- -Consist of epithelial cells that take up large quantities of lipids
- -Cells die and release lipid (sebum) into the hair follicle
- -Sebum has antibacterial and antifungal properties
- -These glands are found over most of the body; highly concentrated in face and scalp
- -A type of holocrine gland
- -Lipids are excreted with remnants of a dead cell
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Facts about Merocrine sweat glands
- -Coiled tubular glands opening onto skin surface
- -Ducts release sweat onto skin surface when body temperature increases
- -Sweat evaporates cooling the skin surface
- -Sweat composition: water, NaCl, urea, uric acid, ammonia
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Properties of Apocrine sweat glands
- -Release a viscous, odorless fluid
- -Bacterial decomposition of fluid creates a distinctive scent
- -Found in axillary and ano-genital regions
- -Fluid is released onto hair follicles
- -Controlled by ANS
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Properties of Skin Receptors
- -Responsible for touch-pressure, tactile perception, hot-cold, pain and itching
- -Most are found within dermal layer
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Types of Sensory Receptors
- -Free nerve endings - pain/temperature
- -Ruffini's endings - pressure/vibration
- -Pacinian corpuscles - touch receptors
- -Meissner's corpuscles - touch receptors
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Properties of Nails
- -Plates of keratinized epithelial cells
- -Nail root is source of dividing cells for growth
- -Cuticle is formed from the stratum corneum
- -Nail bed contains basale and spinosum only
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Facts about nail growth
- -Matrix - proximal portion of nail bed contains dividing cells
- -Cells divide, more distally and are cornified at proximal part of nail plate
- -Nail plate "slides" forward over nail bed as new nail material is added
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Facts about hair follicle
- -Derived from invaginations of epidermal cells
- -Dermal papilla contains dividing cells for hair growth and blood supply
- -Erector pili muscle contraction causes "goose bumps"
- -Melanocytes provide pigment for hair color
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Facts about Hair Growth
- -Hair grows approx. 6 inches/yr, random growth cycles
- -3 phases: Catagen, Telogen, Anagen
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Catagen
- -3% of all hairs
- -2-3 week phase
- -No growth occuring
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Telogen
- -10-15% of all hairs
- -Lasts 100+ days
- -Full resting phase; no growth occurs, hair loss
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Anagen
- -Active growth phase
- -30-45 days up to 2-6 years
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Effects of Aging on skin
- -Atrophy of strata of skin (layers become thinner and more fragile)
- -Reduced elasticity
- -Areas of skin exposed to sun are affected more rapidly
- -Reduced sweat capability
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Effect of Acute Activity on skin causes:
- -blood flow to skin to decrease with activity levels >50%
- -Vasoconstriction and dilation control sin blood flor and may be altered by hot environments
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Effects of chronic Training on Skin
- -Hyperplasia of skin (callous formation)
- -Increased ability to sweat (Improved thermoregulatory ability
- -Blisters
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Describe a blister
- -Fluid deposition at junction of epidermis and dermis
- -Epidermis to be raised away from the dermis
- -Most commonly caused by excessive shearing forces
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Effects of Immobilization on skin
- -Increased risk of skin breakdown = pressure ulcer
- -High pressure areas include: Heels, sacrum, greater trochanter, scapula, elbows, back of the head
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Epidermal Specialization on Back, abdomen, thighs, arms
- -thin epidermis, loosely packed keratin
- -Few follicles produce fine hairs, variable eccrine glands
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Sole of foot specializations
- -Thick epidermis, densely packed ekratin
- -Developed epidermal ridge system
- -No hair follicles, abundant eccrine glands
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Scalp epidermal specializations
-tightly packed follicles
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Fingertip epidermal specializations
-Thick epidermis, developed ridges, abundant sensory receptors
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Axilla/groin epidermal specializations
- -Thin epidermis, numerous oblique hair follicles
- -Numerous eccrine and apocrine glands
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