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The Integumentary System (The 3 Layers of the Skin (Epidermis: top layer…

- - - - 25-30 layers of flat dead cells filled with keratin and surrounded by lipids
      - continuously sheds
      - barrier to light, heat, water, chemical and bacteria
      - friction stimulates callus formation
      - 3/4 of the total epidermal thickness
    - - 3-5 layers of clear, flat, dead cells
      - seen in thick skin on palms and soles of feet, most skin lack this layer
      - contains precursor of keratin
    - - 3-5 layers of flat dying cells
      - show nuclear degeneration
      - diamond-shaped keratocytes
      - contains dark-staining keratohyalin granules, lamellar granules that release lipid (water proofing)
    - - 8-10 layers held together by desmosomes
      - langerhan's cell found in this layer
        
        the purpose of these cells is to phagocytes micro-invaders, the originated I bone marrow and then migrated to the skin
      - during slide preparation, cells shrink and look spiny
      - melanin taken in by phagocytosis from nearby melanocytes
        
        Melanocytes are cells that produce melanin (gives skin pigment), its located in the deepest layer of the epidermis
    - - single layer of keratocytes which are actively engaged in cell division
      - cells attached to each other and to basement membrane via desmosomes hemidesmosomes
      - combination of Merkel cells, melanocytes, keratinocytes and stem cells that divide repeatedly
        
        Merkel cells: they thought to aid in sense of touch and are located in the epidermal-dermal junction
        
        Keratinocytes: they produce keratin and it gives skin its resiliency and strength. they push the older cells toward the outer layers
  - - - underneath the epithelial tissue and composed of loose connective tissue and elastic fibers
      - functions:
        
        looping blood vessels provide nourishment to the active cells of epidermis
        
        Nerve and pain receptors
        
        Thermoregulation receptors
    - - composed of dense irregular connective tissue and collagen fibers set the boundary between the two layers
      - Functions:
        
        provides strength, extensibility and elasticity to skin; stretch marks are dermal tears from extreme stretching
- - - - same number of melanocytes in everyone, but differing amounts of pigment produced
        
        results vary from yellow to tan to black color
      - melanocytes convert tyrosine to melanin
        
        UV in sunlight increases melanin production
    - - freckles or liver spots= melanocytes in a patch
      - Albinism= inherited lack of tyrosinase; no pigment
      - Vitiligo: autoimmune loss of melanocytes in areas of skin produces white patches
    - - Yellow-orange pigment (precursor of vitamin A)
      - found in both stratum corneum and dermis
    - - Red, oxygen carrying pigment in blood cells
      - if other pigments are not present then epidermis is translucent so pinkies will be evident
  - - - yellowish color to skin and whites of eyes
      - build up of yellow bilirubin in blood from liver disease
    - - bluish in color to nail beds and skin
      - Hemoglobin depleted of oxygen looks purple-blue
    - - redness of skin due to enlargement of capillaries in dermis
      - during inflammation, infection, allergy or burns
- - - - trapping insulating layer of air
      - maintains body temp
    - - guard hair
      - wool type hair
      - tactile hair
        
        also called sinus hairs because of large blood-filled sinuses that surround the deep portions of the follicle
        
        thicker, longer than guard hairs. also very sensitive to movement
        
        Used as probes/feelers and found on face, lips, and eyes
    - - shaft-visible
        
        medulla (center of hair shaft), cortex (melanin), and cuticle (outer)
        
        CS round in straight hair
        
        CS oval in wavy hair
      - root-below surface
      - follicle surrounds root
      - Structure of hair follicle:
        
        Invaginate as a double-layered root sheath which surrounds hair and ends in a hair bulb
        
        Hair build surrounds dermal papilla
        
        internal epithelial root sheath: its next to root of hair and continuous w/ dermal papilla
        
        external epithelial root sheath: continuous w/ epidermis and gives rise to sebaceous glands
      - Hair related structure: arrestor pili muscle
        
        smooth muscle in Demis contracts w/ cold or fear
        
        forms goosebumps as hair is pulled vertically
        
        innervated sympathetic nervous system: fight or flight reactions to increase body size
  - - - located all over the body and associated w/ hair follicle. arrestor pili muscles aid in secretion
      - oily, lipid secretions
      - Halocrine structure: gland in which cell is liberated at secretion
    - - located all over body
      - produce a watery transparent liquid (sweat) that helps cool the body
      - eccrine sweat glands: simple coiled tube located in dermis or hypodermis and empty into the epidermis; its on skin
      - Apocrine sweat glands: coiled tube located in dermis or hypodermis and empty into a hair follicle; on hair follicles
      - Horse only one that sweats regularly
        
        sweat glands sensitive to epinephrine, why a nervous horse sweats a lot
        
        sweat very rich in protein, why they foam or lather up
        
        sweat high in potassium
- - - - releasing of sweat onto the skin
      - adjusting flow of blood to the body surface
        
        moderate exercise: more blood brought to surface helps lower temp
        
        extreme exercise: blood is shunted to muscle and body temp rises
      - shivering and construction of surface vessels
    - - tight cell junctions prevent bacterial invasion
      - lipids released retard evaporation
      - pigment protects somewhat against UV light
      - Langerhans cells alert immune system
    - - touch, temp, pressure, vibration, tickling and some pain sensation arise from the skin
    - - only a minor role by skin
      - 400 mL of water evaporates from it daily, small amount of salt, CO2, ammonia and urea are excreted
      - lipid soluble substances can be absorbed through the skin
        
        Vitamin A,D, and K
        
        oxygen and CO2
    - - sunlights activate a precursor to vitamin D
      - enzymes in the liver and kidneys transform that molecules into calcitriol (most active from of vitamin D)
  - - - abrasion or minor burn (superficial wounds)
      - basal cells migrate across the wound
      - contact inhibition with other cells stop migration
      - epidermal growth factor stimulates cell division
      - full thickness of epidermis results from further cell division
    - - Inflammatory phase: clot unite wound edges and WBC's arrive from dilated and more permeable blood vessels
      - Migratory phase: regrowth of epithelial cells and formation of scar tissue by fibroblasts
      - proliferative phase: completion of tissue formation
      - maturation phase: scab falls off
      - scar formation:
        
        hypertrophic scar remain w/in the boundaries of the original wound
        
        keloid scar extends into previously normal tissue