skel3

• Integumentary system


  Composed of the skin, hair, oil and sweat glands, nails and sensory receptors
• Integumentary system


  • Helps maintain a constant body temperature, protects the body, and provides sensory information about the surrounding environment
• Dermatology


  Medical specialty that deals with the structure, function, and disorders of the integumentary system
• Skin


  Covers the external surface of the body and is by weight the largest organ of the body
• Layers of the skin

  • Epidermis
  • Dermis
  • Subcutaneous tissue
• Epidermis


  • Superficial, thinner portion, composed of epithelial tissue; Avascular
• Dermis


  • Thicker connective tissue portion; dermis is highly vascular
• Subcutaneous tissue


  • Also called the hypodermis; the tissue consists of areolar and adipose tissues; It also contains nerve endings called "lamellar corpuscles" or Pacinian corpuscles that are sensitive to pressure
• Cell types in the epidermis

  • Keratinocytes (85%)
  • Melanocytes (8%)
  • Dendritic cells
  • Tactile epithelial cells
• Keratinocytes


  Produce a fibrous protein called "keratin"; Also produce lamellar granules, which release a water-repellent sealant that decreases water entry and loss and inhibits the entry of foreign materials
• Melanocytes


  Pigment producing cells of the body; Produce the pigment melanin (yellow-red or brown-black pigment)
• Dendritic cells (Langerhans cells)


  Arise from red bone marrow and migrate to the epidermis, where they constitute about 5% of the epidermal cells; Involved in immune response
• Tactile epithelial cells (Merkel cells)


  Least numerous (2%); Located in the deepest layer; They make contact with the flattened process of a sensory neuron (nerve cell), called a non-encapsulated sensory corpuscle or Merkel disc
• Layers of the epidermis

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum
• Stratum basale (Stratum germinativum)


  Deepest layer; Single-row of cuboidal or columnar keratinocytes; Some cells are stem cells that undergo cell division; Contains keratin intermediate filaments (tonofilaments)
• Stratum spinosum


  Superficial to stratum basale; Numerous keratinocytes arranged in 8-10 layers with bundles of keratin intermediate filaments
• Stratum granulosum


  1. 5 rows of flattened keratinocytes, in which organelles are beginning to degenerate; Cells contain "keratohyalin" and "lamellar granules"
• Stratum lucidum


  Present only in skin of palms, palmar surfaces of digits, soles, and plantar surfaces of toes; Consists of 4-6 rows of clear, flat, dead keratinocytes with large amounts of keratin
• Stratum corneum


  Few to 50 or more rows of dead, flat keratinocytes that contain mostly keratin
• Dermis


  • Composed of irregular connective tissue containing collagen and elastic fibers; Woven network of fibers has great tensile strength and ability to stretch and recoil easily; Much thicker than epidermis
• Layers of the dermis

  • Papillary dermis
  • Reticular dermis
• Papillary dermis


  About 1/5 of thickness of the total layer; Contains thin collagen and fine elastic fibers; Surface area is increased by dermal papillae; Contains capillary loops and tactile receptors
• Reticular dermis


  Attached to subcutaneous tissue; Contains bundles of thick collagen fibers, scattered fibroblast, and various wandering cells; Collagen fibers are arranged in netlike manner
• Epidermal ridges


  Produced during the 3rd month of fetal development; Follow the contour of the dermal papillae of the papillary dermis; Form fingerprints
• Melanin


  Causes the skin's color to vary from pale yellow to reddish-brown to black; Pheomelanin is yellow to red, Eumelanin is brown to black; Synthesized by melanocytes in melanosomes; Serves a protective function by absorbing UV radiation
• Hemoglobin


  Red color; The oxygen-carrying pigment in red blood cells
• Carotene


  Yellow-orange pigment that gives egg yolks and carrots their color; Precursor of Vitamin A stored in the stratum corneum and fatty areas of the dermis and subcutaneous tissue
• Albinism


  Inherited inability of an individual to produce melanin; Melanocytes are unable to synthesize tyrosinase
• Vitiligo


  Partial or complete loss of melanocytes from patches of skin produces irregular white spots; Due to immune system malfunction
• Accessory structures of the skin

  • Hair
  • Skin glands
  • Nails
• Hair


  • Present on most skin surfaces except the nipples, the palms, palmar surfaces of the fingers, the soles, the plantar surface of the toes, and labia minora, and prepuce of the penis; Hair shaft and hair root consist of three concentric layers of cells: medulla, cortex, and cuticle of hair
• Functions of the skin

  • Thermoregulation
  • Blood reservoir
  • Cutaneous sensations
  • Synthesis of Vitamin D (Calcitriol)
• Types of wound healing

  • Epidermal wound healing
  • Deep wound healing
• Epidermal wound healing


  1. Epidermal stem cells surrounding the wound break contact with the basement membrane

  2. The cells will enlarge and migrate across the wound

  3. The cells appear to migrate as a sheet until advancing cells from opposite sides of the wound meet

  4. When epidermal cells encounter one another, they stop migrating due to cellular response called "contact inhibition"
• Skin structures


  • Labia minora
  • Prepuce of the penis
• Hair shaft components


  • Superficial portion
  • Deep to the shaft that penetrates into the dermis
• Hair shaft and root

  • They both consist of three concentric layers of cells: medulla, cortex, and cuticle of hair
• Medulla


  Lacking in thinner hair, is composed of two or three rows of irregularly shaped cells that contain large amounts of pigment granules in dark hair, small amounts in gray hair, and lack of pigment granules and presence of air bubbles in white hair
• Cortex


  Forms the major part of the shaft and consist of elongated cells
• Cuticle


  Outermost layer; consists of single layer of thin flat cells that are most heavily keratinized