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Lect 5   intergumentary
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Lect 5 intergumentary






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    Lect 5   intergumentary Lect 5 intergumentary Presentation Transcript

    • Chapter 5 The Integumentary System Lecture Outline
      • The skin and its accessory structures make up the integumentary system.
      • The integumentary system functions to guard the body’s physical and biochemical integrity, maintain a constant body temperature, and provide sensory information about the surrounding environment.
      • Skin and its accessory structures
        • structure
        • function
        • growth and repair
        • development
        • aging
    • STRUCTURE OF THE SKIN (Figure 5.1)
      • The superficial portion of the skin is the epidermis and is composed of epithelial tissue.
      • The deeper layer of the skin is the dermis and is primarily composed of connective tissue.
      • Deep to the dermis is the subcutaneous layer or hypodermis. ( not a part of the skin)
        • It consists of areolar and adipose tissue.
        • fat storage, an area for blood vessel passage, and an area of pressure-sensing nerve endings.
    • Overview of Epidermis
      • Stratified squamous epithelium
      • avascular (contains no blood vessels)
    • Four Principle Cells of the Epidermis – Figure 5.2
      • keratinocytes
        • produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes, and chemicals, and lamellar granules, which release a waterproof sealant
      • melanocytes
        • produce the pigment melanin which contributes to skin color and absorbs damaging ultraviolet (UV) light
      • Langerhans cells
        • derived from bone marrow
        • participate in immune response
      • Merkel cells
        • contact a sensory structure called a tactile (Merkel) disc and function in the sensation of touch
    • Layers (Strata) of the Epidermis
      • Stratum corneum
      • Stratum lucidum
      • Stratum granulosum
      • Stratum spinosum
      • Stratum basale
    • Stratum Basale ( stratum germinativum)
      • Stratum corneum
        • Barrier to light, heat, water, chemicals & bacteria
        • Lamellar granules in this layer make it water-repellent.
      • Stratum lucidum
        • Contains precursor of keratin
      • Stratum granulosum
        • transition between the deeper, metabolically active strata and the dead cells of the more superficial strata
      • Stratum spinosum
        • provides strength and flexibility to the skin
      • Stratum basale
        • Deepest single layer of epidermis
    • Dermis (Figure 5.1)
      • Connective tissue layer composed of collagen & elastic fibers, fibroblasts, macrophages & fat cells
      • Contains hair follicles, glands, nerves & blood vessels
      • Two major regions of dermis
        • papillary region
        • reticular region
    • Dermis - Papillary Region
      • Top 20% of dermis
      • areolar connective tissue containing fine elastic fibers, corpuscles of touch (Meissner’s corpuscles), adipose cells, hair follicles, sebaceous glands, sudoriferous glands
        • The collagen and elastic fibers provide strength, extensibility (ability to stretch), and elasticity (ability to return to original shape after stretching) to skin.
      • Finger like projections are called dermal papillae
        • anchors epidermis to dermis
        • contains capillaries that feed epidermis
        • contains Meissner’s corpuscles (touch) & free nerve endings for sensations of heat, cold, pain, tickle, and itch
    • Dermis - Reticular Region
      • Dense irregular connective tissue
      • Contains interlacing collagen and elastic fibers
      • Packed with oil glands, sweat gland ducts, fat & hair follicles
      • Provides strength, extensibility & elasticity to skin
        • stretch marks are dermal tears from extreme stretching
      • Epidermal ridges form in fetus as epidermis conforms to dermal papillae
        • fingerprints are left by sweat glands open on ridges
        • increase grip of hand
    • Dermis -- Structure
      • Epidermal ridges increase friction for better grasping ability and provide the basis for fingerprints and footprints. The ridges typically reflect contours of the underlying dermis.
      • Lines of cleavage in the skin indicate the predominant direction of the underlying collagen fibers. Knowledge of these lines is especially important to plastic surgeons.
    • Basis of Skin Color
      • The color of skin and mucous membranes can provide clues for diagnosing certain problems, such as
        • Jaundice
          • yellowish color to skin and whites of eyes
          • buildup of yellow bilirubin in blood from liver disease
        • Cyanosis
          • bluish color to nail beds and skin
          • hemoglobin depleted of oxygen looks purple-blue
        • Erythema
          • redness of skin due to enlargement of capillaries in dermis
          • during inflammation, infection, allergy or burns
    • Skin Color Pigments
      • Melanin produced in epidermis by melanocytes
        • melanocytes convert tyrosine to melanin
          • UV in sunlight increases melanin production
      • The wide variety of colors in skin is due to three pigments - melanin, carotene, and hemoglobin (in blood in capillaries) - in the dermis.
      • Carotene in dermis
        • yellow-orange pigment (precursor of vitamin A)
        • found in stratum corneum & dermis
      • Hemoglobin
        • red, oxygen-carrying pigment in blood cells
        • if other pigments are not present, epidermis is translucent so pinkness will be evident
    • Accessory Structures of Skin
      • develop from the embryonic epidermis
      • Cells sink inward during development to form:
        • hair
        • oil glands
        • sweat glands
        • nails
    • Structure of Hair
      • Shaft -- visible
      • Root -- below the surface
      • Follicle surrounds root
      • Functions of Hair
        • P revents heat loss
        • Decreases sunburn
        • Eyelashes help protect eyes
        • Touch receptors (hair root plexus) senses light touch
    • Glands of the Skin
      • Specialized exocrine glands found in dermis
      • Sebaceous (oil) glands
      • Sudiferous (sweat) glands
      • Ceruminous (wax) glands
      • Mammary (milk) glands
    • Sudoriferous (sweat) glands
      • Eccrine sweat glands have an extensive distribution most areas of skin
        • secretory portion is in dermis with duct to surface
        • ducts terminate at pores at the surface of the epidermis.
        • regulate body temperature through evaporation (perspiration)
        • help eliminate wastes such as urea.
      • Apocrine sweat glands are limited in distribution to the skin of the axilla, pubis, and areolae; their duct open into hair follicles.
        • secretory portion in dermis
        • duct that opens onto hair follicle
        • secretions are more viscous
    • Ceruminous Glands
      • Ceruminous glands are modified sudoriferous glands that produce a waxy substance called cerumen.
        • found in the external auditory meatus
        • contains secretions of oil and wax glands
        • barrier for entrance of foreign bodies
      • An abnormal amount of cerumen in the external auditory meatus or canal can result in impaction and prevent sound waves from reaching the ear drum (Clinical Application).
    • Structure of Nails (Figure 5.5)
      • Tightly packed keratinized cells
      • Nail body
        • visible portion pink due to underlying capillaries
        • free edge appears white
      • Nail root
        • buried under skin layers
        • lunula is white due to thickened stratum basale
      • Eponychium (cuticle)
        • stratum corneum layer
    • Sebaceous (oil) glands
      • Sebaceous (oil) glands are usually connected to hair follicles; they are absent in the palms and soles
      • Secretory portion of gland is located in the dermis
        • produce sebum
          • contains cholesterol, proteins, fats & salts
          • moistens hairs
          • waterproofs and softens the skin
          • inhibits growth of bacteria & fungi (ringworm)
      • Acne
        • bacterial inflammation of glands
        • secretions are stimulated by hormones at puberty
      • Thin skin
        • covers all parts of the body except for the palms and palmar surfaces of the digits and toes.
        • lacks epidermal ridges
        • has a sparser distribution of sensory receptors than thick skin.
      • Thick skin (0.6 to 4.5 mm)
        • covers the palms, palmar surfaces of the digits, and soles
        • features a stratum lucidum and thick epidermal ridges
        • lacks hair follicles, arrector pili muscles, and sebaceous glands, and has more sweat glands than thin skin.
    • FUNCTIONS OF SKIN -- thermoregulation
      • Perspiration & its evaporation
        • lowers body temperature
        • flow of blood in the dermis is adjusted
      • Exercise
        • in moderate exercise, more blood brought to surface helps lower temperature
        • with extreme exercise, blood is shunted to muscles and body temperature rises
      • Shivering and constriction of surface vessels
        • raise internal body temperature as needed
      • blood reservoir
        • extensive network of blood vessels
      • protection - physical, chemical and biological barriers
        • tight cell junctions prevent bacterial invasion
        • lipids released retard evaporation
        • pigment protects somewhat against UV light
        • Langerhans cells alert immune system
      • cutaneous sensations
        • touch, pressure, vibration, tickle, heat, cold, and pain arise in the skin
      • Synthesis of Vitamin D
        • activation of a precursor molecule in the skin by UV light
        • enzymes in the liver and kidneys modify the activated molecule to produce calcitriol, the most active form of vitamin D.
        • necessary vitamin for absorption of calcium from food in the gastrointestinal tract
      • excretion
        • 400 mL of water/day, small amounts salt, CO2, ammonia and urea
    • Epidermal Wound Healing
      • Abrasion or minor burn
      • Basal cells migrate across the wound
      • Contact inhibition with other cells stops migration
      • Epidermal growth factor stimulates basal cells to divide and replace the ones that have moved into the wound
      • Full thickness of epidermis results from further cell division
    • Deep Wound Healing
      • When an injury extends to tissues deep to the epidermis, the repair process is more complex than epidermal healing, and scar formation results.
      • Healing occurs in 4 phases
        • inflammatory phase has clot unite wound edges and WBCs arrive from dilated and more permeable blood vessels
        • migratory phase begins the regrowth of epithelial cells and the formation of scar tissue by the fibroblasts
        • proliferative phase is a completion of tissue formation
        • maturation phase sees the scab fall off
      • Scar formation
        • hypertrophic scar remains within the boundaries of the original wound
        • keloid scar extends into previously normal tissue
          • collagen fibers are very dense and fewer blood vessels are present so the tissue is lighter in color
    • Deep Wound Healing
      • Phases of Deep Wound Healing
        • During the inflammatory phase , a blood clot unites the wound edges, epithelial cells migrate across the wound, vasodilatation and increased permeability of blood vessels deliver phagocytes, and fibroblasts form
        • During the migratory phase , epithelial cells beneath the scab bridge the wound, fibroblasts begin scar tissue, and damaged blood vessels begin to grow. During this phase, tissue filling the wound is called granulation tissue .
    • Phases of Deep Wound Healing
    • Deep Wound Healing
      • Phases of Deep Wound Healing
        • During the proliferative phase , the events of the migratory phase intensify.
        • During the maturation phase , the scab sloughs off, the epidermis is restored to normal thickness, collagen fibers become more organized, fibroblasts begin to disappear, and blood vessels are restored to normal
        • Scar tissue formation (fibrosis) can occur in deep wound healing.
    • Age Related Structural Changes
      • Collagen fibers decrease in number & stiffen
      • Elastic fibers become less elastic
      • Fibroblasts decrease in number
      • decrease in number of melanocytes (gray hair, blotching)
      • decrease in Langerhans cells (decreased immune responsiveness)
      • reduced number and less-efficient phagocytes
      • Most of the changes occur in the dermis
        • wrinkling, slower growth of hair and nails
        • dryness and cracking due to sebaceous gland atrophy
        • Walls of blood vessels in dermis thicken so decreased nutrient availability leads to thinner skin as subcutaneous fat is lost.