Integumentary system (Skin)

Consists of the skin, hair, oil, sweat glands, nails and sensory receptors.
1. Functions of the skin
  1. Regulates body temperature
  2. Stores blood
  3. Protects body from external environment
    1. E.g Chemicals. Sunlight. Water loss. Microbes.
  4. Detects sensations
  5. Excretes and absorbs substances
    1. E.g. urea in sweat. Sebum.
  6. Synthesises vitamin D
SKIN STRUCTURE
1. EPIDERMIS
  1. DERMIS
    1. HYPODERMIS
      1. Subcutaneous layer of loose, fibrous connective tissue
    2. Inside layer
  2. Outside layer
  3. Dermo-Epidermal junction
    1. Basement membrane that joins the Epidermis & Dermis
      1. Composed of 3 layers:(Top) lamina lucida, lamina densa and lamina fibroreticularis (Bottom)
        RETE RIDGES - projections down the way form the epidermis to the dermis. DERMAL PAPILLAE - nipple shaped structures project into the undersurface of the epidermis.
        Rete Ridges increase surface area for molecules passing between dermis and epidermis. Networks of tiny blood vessels run through the ridges, bringing food, vitamins and oxygen to the epidermis.
        Rete Ridges are not present in the skins of unborn babies. Ageing skin - rete ridges get smaller and flatter.
  4. 5 layers of the epidermis
    1. Stratum Corneum
      1. Consists of large, flat, dead cells (10-30 cells thick) - keratinocytes/corneocytes arranged in parallel rows
      2. Cells have lost all organelles and most water content
      3. Cells are continuously shed and replaced by cells from the deeper strata. It's key role is to prevent loss of moisture from tissues through evaporation - Transepidermal water loss
      4. Intercellular space filled with cement which holds the cells together.
      5. This keratinised layer consists of a soft keratin which helps keep the skin elastic
      6. CORNIFIED ZONE - DEAD OR DYING CELLS
    2. Stratum Lucideum
      1. Body has 'thick' (glabrous/non-hairy) skin
      2. Only appears in palms of hands and soles of feet
      3. Acts as a protective shield against UV rays
      4. Consists of 3-5 layers of flattened, clear, dead cells.
      5. Contains a protein called Eleidin
    3. Stratum Granulosum
      1. Usually 3 to 5 layers thick of flattened keratinocytes
      2. Keratinisation process begins
        Newly formed cells in the St. Basale are slowly pushed to the surface. As the cells move from one epidermal layer to the next, they accumulate more and more keratin.
      3. Cells begin to die - the nuclei begins to disintegrate (lysosomes) along with other cellular organelles
      4. The cells become flattened and accumulate large granules called keratohyaline.
    4. Stratum Spinosum
      1. 8-10 layers of many sided keratinocytes fit closely together
        Linked by desmosomes
        Provides strength and flexibility to skin
      2. Cell division & growth occuring
        Cells possess large amounts of keratin filament bundles
      3. Spiny/prickly layer
      4. Contains non-keratinocyte cells called Langerhans cells
      5. Cytoplasm contains numerous polyribosomes & melanin granules derived from epidermal melanocytes.
    5. Stratum Germinativum/Basale
      1. Composed of a single row of cuboidal or columnar keratinocytes.
        Cells have an oval nucleus, prominent nucleoli, little heterochromatin (responsible for DNA/genes).
        Have many mitochondria, free ribosomes, nuclei, may also have cytoskeletal filaments (actin micro filaments and keratin filament bundles) and Tonofilaments.
        Mitochondria - powerhouses of cell
        Cytoskeletal - filaments - give the skeleton to the cell itself.
        Tonofilaments - made up of keratin converge together at the site of the desmosome.
      2. Some cells in this layer are stem cells that undergo cell division (MITOSIS) to continually produce new KERATINOCYTES.
      3. Sits on basement membrane next to the dermis
      4. Cells attached to the basement membrane by HEMIDESMOSOMES
      5. Also contains Melanocytes and Merkel cells - both are types of Non-Keratinocyte cells
      6. MALPIGHIAN LAYER - ACTIVE/GROWING CELLS
  5. EPIDERMOPOIESIS
    1. Cells being made/cell growth
  6. Consists of stratified squamous epithelium.
    1. There is continuous replacement of cells. Renewed every 15-30 days.
      1. Does not contain blood vessels - AVASCULAR
        It is translucent.
        The palms and soles are thicker
  7. Cells of the Epidermis - Keratinocytes - 90% of epidermal cells. Melanocytes - 10% - found mainly in Basale layer.
  8. Langherhans cells (dendritic cells) found in Spinosum layer - important in immune reactions. Merkel cells (dendritic cells) are found in Basale layer - gather sensory information (touch). Form desmosomes with keratinocytes.
Integumentum means COVER
4.5-5 Kilos - skin weight of a normal adult
1. 2m2 - surface area of skin
  1. 0.5mm thick -eyelids to 5mm think - upper back.
    1. We lose about 30-40k of cells every minute
      1. 19 million cells are in each square inch of human skin
        32 million bacteria are found on each square inch of human skin
Langer's/Cleavage Lines - lines of tension within the skin. Surgeons try to follow when making incisions - heaiing is faster and scarring is minimal
SKIN PIGMENTATION
1. The difference in pigmentation that determines racial types is in the number of MELANOSOMES, i.e. the organelle within the melanocyte that produces pigment.
2. Disorders of Pigmentation: Albinism (involves a lack of Tyrosine), Vitiligo, Freckles

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Integumentary system (Skin)

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	Created by Morgan Morgan over 10 years ago