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Skin and Derivatives of Skin. Main Layers of Skin. Epidermis (outer layer) Dermis (inner layer). Epidermis. Functions Protection against physical, chemical, and radiation injury.

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main layers of skin
Main Layers of Skin
  • Epidermis (outer layer)
  • Dermis (inner layer)
  • Functions
    • Protection against physical, chemical, and radiation injury.
    • Protection against microorganisms (by barrier, by bacterial binding to cells which will be released and by some phagocytosis)
    • Reduction of fluid loss
sub layers of epidermis
Sub-layers of Epidermis
  • Basal lamina – separates epidermis from dermis
  • Stratum basale
    • Deep layer contains living cells that divide to produce new cells
  • Stratum spinosum
  • Stratum granulosum
  • Stratum corneum
    • Surface layer of dead cells
stages of epidermal cell development
Stages of Epidermal Cell Development
  • Synthetic Stage
    • Most cells found in lower part of spinosum layer
    • Synthesis of specific proteins and lipids (protein filaments, a polar lipid material that will be released from the cell, and keratohylain granules which will form the protein keratin)
stages continued
Stages (Continued)
  • Transformation Stage
    • Occurs in layers below Stratum corneum
    • Intracellular enzymes are released that attack and lyse all organelles
    • Keratohyalin material fills cell
stages continued8
Stages (Continued)
  • Terminal Stage
    • Excessive loss of fluid from cells
    • The narrow intracellular space becomes filled with lipid material
    • Cells at the end of this stage are found in upper Stratum corneum layer
dermis of skin
Dermis of Skin
  • Thick layer of:
    • Fibrous connective tissue (anchoring fibers, collagen fibers, elastic fibers)
    • Muscle tissue
    • Adipose tissue
    • Blood vessels
    • Nerves including sensory receptors
dermal structures of epidermal origin
Dermal Structures of Epidermal Origin
  • Sebaceous Glands
    • usually associated with hair follicles – serve primarily to lubricate hair
    • These glands are important in waterproofing the pelage
    • Secretions are mainly cellular debris and lipids (oils) from cells that breakdown
    • Androgens stimulated these glands
structures continued
Structures (Continued)
  • Sweat Glands
    • Hypotonic secretions that contain a lot of water
      • Apocrine Type – open into a hair follicle
      • Eccrine Type – open onto the surface of the skin independent of a hair follicle
        • Responsible for most of the sweat that is produced
structures continued12
Structures (Continued)
  • Sweat functions in
    • Evaporative Cooling
    • Improving tactile sensitivity
  • No sweat glands in – Cetaceans, Sirenians, Elephants, Pangolins, Echidnas, Moles, Rodents
structures continued13
Structures (Continued)
  • Only apocrine sweat glands in – Bats, some primitive primate species
  • More eccrine than apocrine sweat glands in – higher primates and humans
structures continued14
Structures (Continued)
  • Scent glands
    • May be modified sebaceous glands or modified sweat glands
    • Used for defense, territory marking, orientation, social interactions
structures continued15
Structures (Continued)
  • Hair
    • Hair is a keratinized derivative of the epidermis which is found in all mammals at some point in life cycle
    • Structure is
      • Central medulla (continuous or with air spaces)
      • Cortex which constitutes bulk of hair follicle
      • Cuticle (layer of outer scales that vary in shape)
types of hair
Types of Hair
  • Vibrissae – Long, stiff hairs well well innervated bases, tactile receptors, definitive growth
  • Guard Hairs – Serve primarily for protection
    • Spines – enlarged, stiff guard hairs, ex. quills of porcupines, definitive growth, shed and replaced periodically
types of hair continued
Types of Hair (Continued)
  • Guard Hairs (Continued)
    • Bristles – long, firm hairs with angora growth, ex. horse and lion manes
    • Awns – firm, expanded distal portion with smaller base, definitive growth
types of hair continued18
Types of Hair (Continued)
  • Underhair – primarily for insulation
    • Wool – long, angora growth
    • Fur – short, definitive growth
    • Velli – down or fuzz, first hair on an animal
color of hair
Color of Hair
  • Pigment molecules
    • Eumelanin – provides shades of black and brown
    • Pheomelanin – produces shades of red and yellow
pigment in cells
Pigment in Cells
  • Contained in melanosomes within melanocytes
  • Melanosomes are transferred from melanocytes to epithelial cells that become keratinocytes
  • Pigment in melanocytes and keratinocytes shield stratum basale from UV radiation
  • Pigment also acts as free radical scavenger, preventing cellular damage
pigment in hair
Pigment in Hair
  • Melanocytes transfer melanosomes to epithelial cells at base of hair shaft
  • Melanosomes are phagocytized by cells that will form the cortex of the hair shaft
head ornaments
Head Ornaments
  • Occur only in Orders Artiodactyla and Perissodactyla
true horns
True Horns
  • Found only in Family Bovidae of O. Artiodactyla
    • An inner core of bone from the frontal bone and a sheath of keratinized epidermis
    • Grow continuously throughout life of animal
    • Unbranched
    • Never shed
    • Usually in males but can be in females too
  • Found only in Pronghorn antelope (F. Antilocapridae, O. Artiodactyla)
    • Similar in structure to true horns except
      • Sheath is shed annually
      • Sheath is branched but bone is not
      • Occur in males and some females, horn on female may be smaller than on male and could be unbranched
giraffes horns
Giraffes Horns
  • F. Giraffidae of O. Artiodactyla
    • Derive from separate bony ossifications that fuse to the skull near the junction of the parietal and frontal bones (are not projections from frontal bone!)
    • Permanently covered by skin and hair
    • Occur in both sexes
rhinoceros horns
Rhinoceros Horns
  • O. Perissodactyla
  • Horn is composed of large mass of elongated, dermal papillae that fuse to form the horn
  • No core of bone
  • Horn is really keratinized skin
  • F. Cervidae of O. Artiodactyla
    • Made entirely of bone
    • Branched
    • Outgrowths of frontal bone
    • Shed annually
    • Covered by “velvet” while growing
    • Size cannot be used to directly age and animal, size depends upon nutritional state