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Flashcards in Skin IA%% (+ Deck (20):

Skin as an Organ

•Combination of the 4 primary tissues: epithelium, connective tissue, muscle, nerve.

•Epidermal cells are termed keratinocytes

Largest organ in the body

•Has its own pathological conditions:

 eg. sunburn, acne, eczema, psoriasis (red,crusty patches of skin), melanoma

•Provides  important external evidence of underlying systemic conditions: eg. liver disease, systemic sclerosis (autoimmune disease of the connective tissue), mitral stenosis (a narrowing of the mitral valve opening that blocks blood flow from the left atrium to the left ventricle), urticaria  (rash)


2 layers: Structure 


- Epithelium

- Forms boundary between internal and external compartments


- Connective tissue

- Gives structural strength

Note: Hypodermis

-  Adipose (fatty) CT layer beneath skin = subcutaneous tissue, anchors skin to underlying structures - not part of skin

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4 types of epidermal cells


  • Most frequent, contain keratin (contains sulphur), hard and  resistance to abrasion.
  •  Extrude (force out) lipids – waterproofing.
  • Constantly dividing – self regeneration  protecting from trauma and other damage.


  • pigment formation

Langerhans cells:

  • immune surveillance

Merkel cells:

  • touch receptors

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  • Organic process whereby keratin is deposited in cells and these become horny as in dead skin, nails, hair

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Outer layer of skin (consisting itself of 5 strata = layers)

•Epithelial = Stratified squamous keratinising epithelium

Ectodermal origin

•Prevents water loss by evaporation

•5 layers  formed by maturing keratinocytes​

5 layers (superficial to deep):

  1. Statum corneum
  2. Stratum lucidum
  3. Statum granulosum
  4. Statum spinosum
  5. Statum basale

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Stratum corneum (Stratum lucidum)

  • Stratum lucidum difficult to distinguish from stratum corneum
  • Conversion of keratohyalin ⇒ keratin
  • Lots disulphide linkages give strength
  • Stratum corneum  has no organelles
  • Desmosomes bind cells
  • 15-30 day turnover

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Stratum granulosum

  • Presence of granules defines the layer
  • Keratohyalin (possible precursors of keratin) are in Granules 


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Stratum spinosum

Spinous layer

•Created post-mortem: Cells shrink but desmosome junctions “create” spines

•Little structural evidence of activity

Preparative layer for keratinisation

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Stratum basale (germinativum)

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Tall columnar cells interspersed with melanocytes and Merkel cells

•Cells bound to BM by hemidesmosomes

•Irregular interface with dermis - dermal papillae

•Continuous cell proliferation - are stem cells (undifferentiated)

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Dermis:2 layers

Papillary layer

Loose connective tissue


Reticular layer

–Dense irregular connective tissue


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Dermis: papillary layer

–Loose connective tissue

–Irregular interface with epidermis - “papillae”

Cellular eg macrophages

Protective against pathogens

–Blood vessels: Thermoregulation, Nutrition

–Nerve endings: Sense organ

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Dermis: Reticular layer

Dense irregular connective tissue

Collagen bundles in 3 planes

Elastic fibres

–Loss of elasticity is normal in old age


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Skin- sense and repair

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Meissner’s corpuscles - light touch - fingertips

Paccinian corpuscles - vibration & pressure

•Pain receptors


4 stages

  1. Blood clot
  2. Scab
  3. Granulation tissue
  4. Scar

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Skin colour

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Carotene (Carotenes are photosynthetic pigments important for photosynthesis)

Melanin –Protects against UV

Melanocytes (melanin-producing neural-crest derived cells located in the bottom layer, the stratum basale,of the skin's epidermis)





  • Function of epidermis
  • Keratin in cells “waterproof


  • Melanin –Protects against UV


  • Eccrine sweat glands
  • Blood vessels dialation: absorption/radiation
  • Hair (polar bears, not humans)


  • Hair


Eccrine sweat glands

•Simple tubular glands

•Located in dermis

Coiled secretory portion

•Coiled and straight duct in dermis

•Spiral channel in epidermis

•Watery secretion


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Hair 1

•Derived from epithelial layer

Origin of hair follicles

•From epidermis in utero

Downgrowth of epithelial cells

•Invasion of knot of blood vessels

•Growth of hair

•Continuity with layers of epidermis



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Hair 2 

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•Hair + sheath(s)

•Arrector pili muscles

–Attached to follicle root and base epidermis

–Follicle at angle

–Hair straightens when muscle contracts

•Sebaceous glands

Between follicle and arrector pili muscle

–Secretes sebum (oily, waxy substance called sebum that is made of triglycerides, wax esters. Sebum waterproofs and lubricates the skin and hair of mammals)

–Function uncertain


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  • The distal end of each digit is protected by a strong plate of hard keratin, called a nail or nail plate, which grows out from a nail bed. 
  • The nail bed, is a specialised form of skin epithelium, and has the same 4 layers of the epidermis of skin, with the nail plate being analogous to the stratum corneum layer.

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Skin glands

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Sebaceous glands: secretes a lubricating oily matter, sebum, into the hair follicles

Eccrine glands: the major sweat glands of the human body

Apocrine: sweat glands


–Protein rich - B.O.!

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