Integumentary system (Skin)

Integumentary system (Skin)

1. Consists of the skin, hair, oil, sweat glands, nails and sensory receptors.

   • Functions of the skin
     • Regulates body temperature
     • Stores blood
     • Protects body from external environment
       • E.g Chemicals. Sunlight. Water loss. Microbes.
     • Detects sensations
     • Excretes and absorbs substances
       • E.g. urea in sweat. Sebum.
     • Synthesises vitamin D

2. SKIN STRUCTURE

   • EPIDERMIS
     • DERMIS
       • HYPODERMIS
         • Subcutaneous layer of loose, fibrous connective tissue
       • Inside layer
     • Outside layer
     • Dermo-Epidermal junction
       • Basement membrane that joins the Epidermis & Dermis
         • 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.
     • 5 layers of the epidermis
       • Stratum Corneum
         • Consists of large, flat, dead cells (10-30 cells thick) - keratinocytes/corneocytes arranged in parallel rows
         • Cells have lost all organelles and most water content
         • 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
         • Intercellular space filled with cement which holds the cells together.
         • This keratinised layer consists of a soft keratin which helps keep the skin elastic
         • CORNIFIED ZONE - DEAD OR DYING CELLS
       • Stratum Lucideum
         • Body has 'thick' (glabrous/non-hairy) skin
         • Only appears in palms of hands and soles of feet
         • Acts as a protective shield against UV rays
         • Consists of 3-5 layers of flattened, clear, dead cells.
         • Contains a protein called Eleidin
       • Stratum Granulosum
         • Usually 3 to 5 layers thick of flattened keratinocytes
         • 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.
         • Cells begin to die - the nuclei begins to disintegrate (lysosomes) along with other cellular organelles
         • The cells become flattened and accumulate large granules called keratohyaline.
       • Stratum Spinosum
         • 8-10 layers of many sided keratinocytes fit closely together
           • Linked by desmosomes
           • Provides strength and flexibility to skin
         • Cell division & growth occuring
           • Cells possess large amounts of keratin filament bundles
         • Spiny/prickly layer
         • Contains non-keratinocyte cells called Langerhans cells
         • Cytoplasm contains numerous polyribosomes & melanin granules derived from epidermal melanocytes.
       • Stratum Germinativum/Basale
         • 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.
         • Some cells in this layer are stem cells that undergo cell division (MITOSIS) to continually produce new KERATINOCYTES.
         • Sits on basement membrane next to the dermis
         • Cells attached to the basement membrane by HEMIDESMOSOMES
         • Also contains Melanocytes and Merkel cells - both are types of Non-Keratinocyte cells
         • MALPIGHIAN LAYER - ACTIVE/GROWING CELLS
     • EPIDERMOPOIESIS
       • Cells being made/cell growth
     • Consists of stratified squamous epithelium.
       • There is continuous replacement of cells. Renewed every 15-30 days.
         • Does not contain blood vessels - AVASCULAR
           • It is translucent.
             • The palms and soles are thicker
     • Cells of the Epidermis - Keratinocytes - 90% of epidermal cells. Melanocytes - 10% - found mainly in Basale layer.
     • 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.

3. Integumentum means COVER

4. 4.5-5 Kilos - skin weight of a normal adult

   • 2m2 - surface area of skin
     • 0.5mm thick -eyelids to 5mm think - upper back.
       • We lose about 30-40k of cells every minute
         • 19 million cells are in each square inch of human skin
           • 32 million bacteria are found on each square inch of human skin

5. Langer's/Cleavage Lines - lines of tension within the skin. Surgeons try to follow when making incisions - heaiing is faster and scarring is minimal

6. SKIN PIGMENTATION

   • The difference in pigmentation that determines racial types is in the number of MELANOSOMES, i.e. the organelle within the melanocyte that produces pigment.
   • Disorders of Pigmentation: Albinism (involves a lack of Tyrosine), Vitiligo, Freckles