THE INTEGUMENTARY SYSTEM (6)

• Integumentary system


  The skin and its associated structures
• Skin - is the largest organ of the body in weight
• Two main parts:

  Epidermis

  Dermis
• Epidermis


  Composed of epithelial tissue
• Dermis


  Thicker connective tissue portion
• Functions of the integumentary system

  • Regulates body temperature
  • Stores blood
  • Protects body from external environment
  • Detects cutaneous sensations
  • Excretes and absorbs substances
  • Synthesize vitamin D
• Epidermis


  • Composed of keratinised stratified squamous epithelium
  • Contains four principal types of cells: keratinocytes, melanocytes, intraepidermal macrophages, and tactile epithelial cells
• Dermis


  • Composed of dense regular connective tissue containing collagen and elastic fibres
  • Essential for the survival of epidermis
  • Can be divided into thin superficial papillary region and a thick deeper reticular region
• Keratinocytes


  • Make up about 90% of epidermal cells
  • Arranged in four or five layers
  • Produce the protein keratin to protect the skin and underlying tissues
  • Also produce lamellar granules
• Layers of epidermis

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum
• Stratum basale


  • Deepest layer of the epidermis
  • Composed of single row of cuboidal or columnar keratinocytes
  • Contains stem cells that undergo cell division to produce new keratinocytes
  • Contains melanocytes and tactile epithelial cells
• Stratum spinosum


  • 8 to 10 rows of many-sided keratinocytes with bundles of keratin intermediate filaments
  • Contains projections of melanocytes and intraepidermal macrophages
• Stratum granulosum


  • 3 to 5 rows of flattened keratinocytes
  • Organelles are beginning to degenerate
  • Cells contain the protein keratohyalin and lamellar granules
• Stratum lucidum


  • Only exists in thick areas of skin
  • Consists of 4 to 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
  • Callus and abnormal thickening can occur
• Keratinisation and growth of the epidermis

  1. Newly formed cells in the stratum basale are slowly pushed to the surface

  2. As cells move from one epidermal layer to the next, they accumulate more and more keratin

  3. Cells then undergo apoptosis

  4. Keratinised cells slough off and are replaced by underlying cells that in turn become keratinised

  5. Whole process takes about four to six weeks in an average epidermis of 0.1 mm (0.004 in.) thickness
• Papillary region of dermis

  • Superficial portion of dermis (about one-fifth)
  • Consists of areolar connective tissue with thin collagen and fine elastic fibres
  • Contains dermal ridges that house blood capillaries, corpuscles of touch, and free nerve endings
  • Surface area is greatly increased by dermal papillae
• Reticular region of dermis

  • Deeper portion of dermis (about four-fifths)
  • Consists of dense irregular connective tissue with bundles of thick collagen and some coarse elastic fibres
  • Spaces between fibres contain some adipose cells, hair follicles, nerves, sebaceous gland, and sudoriferous glands
• Subcutaneous layer (hypodermis)


  • Consists of areolar and adipose tissues
  • Serves as a storage depot for fat and contains large blood vessels that supply the skin
  • Contains nerve endings called lamellated corpuscles or Pacinian corpuscles that are sensitive to pressure
• Epidermal ridges


  • Create a strong bond between the epidermis and dermis in a region of high mechanical stress
  • Epidermal ridge pattern is in part genetically determined and is unique for each individual
  • Dermatoglyphics is the study of the pattern of epidermal ridges
• Pigments that impart colour to skin

  • Melanin
  • Hemoglobin
  • Carotene
• Melanin


  Causes the skin's colour to vary from pale yellow to reddish-brown to black
• Hemoglobin

  Causes the red colour due to the oxygen-carrying pigment in red blood cells
• Carotene


  A yellow-orange pigment that gives egg yolks and carrots their colour
• Representative diseases and disorders of the integumentary system

  • Birthmarks
  • Ringworm
  • Eczema and dermatitis
  • Frostbites
  • Psoriasis
  • Vitiligo
  • Alopecia areata
  • Skin cancer
  • Impetigo
  • Erysipelas
  • Decubitus ulcers
  • Acne
  • Rubeola (measles)
  • Rubella (German measles)
  • Chickenpox
  • Shingles
  • Cold sores
  • Genital herpes