7 LAYERS OF THE SKIN (FOR
FLIPBOOK)
STRATUM CORNEUM (HORNY LAYER)
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thick layer of flattened dead cells completely filled with keratin
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cells are continuously shed as dandruff and flakes
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replaced by underlying cells from deeper strata (2 weeks)
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shed about 40 lbs in a lifetime
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forms an effective barrier against light, heat, bacteria and chemicals
KERATINIZATION
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Cells newly formed in the basal layers undergo a developmental process as they are pushed
to the surface
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during relocation they accumulate keratin
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while the cytoplasm, nucleus and other organelles disappear and the cells die
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Epidermal Growth Hormone (EGF)
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Produced by pituitary gland
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stimulates growth of cells (cancerous cells)
STRATUM LUCIDUM (clear layer)
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o ( absent in thin skin )
Thin translucent band of flattened dead keratinocytes
Closely packed, clear cells, nuclei absent
Keratohyaline –tonofilaments � keratin fibrils
Thickest in soles of feet and palms
Cytoplasm filled with eleidin, a water barrier
STRATUM GRANULOSUM (GRANULAR LAYER)
thinner layer
flattened keratinocytes
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waterproofing glycolipid is secreted into the extracellular spaces
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cell plasma membranes are thickened
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nuclei of the cells are in various stages of degeneration
STRATUM SPINOSUM (SPINY LAYER)
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several cell layers thick
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cell division is less frequent than in the basal layer
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contains Langerhans cells
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Langerhans cells help t-cells in the immune response (t-cells are in the lymph)
arise from bone marrow and migrate to the epidermis
easily damaged by exposure to U.V. radiation
STRATUM BASALE (BASAL LAYER)
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attatched to the dermal layer
contains stem cells which give rise to:
keratinocytes
oil glands, sweat glands, hair follicles
contains Merkel cells
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contains Melanocytes
10-25% of the basal layer
pigmented cells which contain melanin
MELANOCYTES
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Produce melanin -a black -brown skin pigment
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melanin accumulates as granule packets on the superficial side of the branched
keratinocytes forming a shield over the nucleus
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melanin absorbs ultraviolet radiation thus protecting the cell DNA from its harmful effects
DERMIS
Strong, flexible connective tissue containing collagen and elastic fibers
Thick in the palms and soles
Extensive blood vessel supply
Glands, hair follicles and nerves are embedded
Two layers
Papillary layer
most superficial layer (20%)
Reticular layer
deeper (80%)
PAPILLARY LAYER
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Areolar elastic connective tissue
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surface area is increased by
projections called dermal papillae
dermal ridges which create "friction ridges" with nerve endings sensitive to touch
o ridges also create "fingerprints"
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RETICULAR LAYER
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80% of dermis
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Netlike, interlacing bundles of collagen and elastic fibers
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help give the skin strength with elasticity and extensibility
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flexure lines around the joints
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small tears in this layer result in the formation of striae "stretch marks”
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lines of cleavage (tension lines) indicate the predominant direction of underlying collagen
fibers (surgical incisions)
HYPODERMIS
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fatty layer, below the skin
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subcutaneous layer of porous areolar and adipose tissues
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carries the major blood vessels and nerves which supply the skin above
ideal for administration of liquid medicines (insulin) by subcutaneous injection
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anchors the skin to muscles
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stores fat to act as an insulator