L1

• skin functions       

  Protective                

  • Barrier against microbial organisms                
  • Against mechanical, chemical, osmotic, thermal, UV radiation damage                
  • Immunological response      

  Biomechanical synthesise                

  • Vit D under influence of UVB      

  Homeostasis                

  • Control body temperature      

  Sweating                

  • Sweat glands      

  Major sensory organ                

  • Touch, temperature, pain etc
• LAYERS OF THE SKIN

  Epidermis

  Dermis

  Hypodermis
• EPIDERMIS

  Self renewing stratified epithelial tissue

  
  

  CELLS in epidermis:

  Mainly keratinocytes

  Langerhans cells

  Merkel cells

  Melanocytes 
• KERATINOCYTES

  Undergo continuous renewal throughout life

  Turnover is mediated by stem cells

  Superficially => More mature
• LANGERHANS CELLS 

  Immune function

  Distributed in both basal and spiny layers
• MERKEL CELLS

  Present in basal lamina

  Sensory nerve ending (light touch sensation)

  Has desmosome connections to keratinocytes
• MELANOCYTES

  Present at the basal lamina

  Produce melanin pigment -> melanosome -> keratinocytes (umbrella)

  Lack desmosome connections with keratinocytes (branching dendrites)

  Present hemidesmosome connection with basal lamina
• All humans have the same number of melanocytes -> just produce differing amounts of melanin
• STRATUM CORNEUM

  Final stage of epidermal differentiation

  Closely packed flattened cells / corneocytes - dead

  Cells lack nucleus and membranous organelles

  Packed with keratin filaments

  Desmosomes weaker
• STRATUM GRANULOSUM

  3-4 layers of flattened cells

  Nuclei and organelles become disintegrated

  Cytokeratin filament bundles become more compact

  Densely strained keratocyte hyaline granules synthesise hydrophobic glycophospholipids which form a water barrier between granular and cornified layer -> hydration and prevents water from evaporating

  Keratohyalin granules + thornofibrils = keratinisation = keratin made go superficially

  
• STRATUM SPINOSUM

  Keratinocytes are closely packed, connected via desmosomes (provide tensile strength)

  Cytoplasm consists of melanosomes

  Langerhans cells also present

  
  

  SPIKY - desmosomes

  
  

  Spiny cells synthesise cytoplasmic intermediate filaments (cytokeratin) which comes together to form thornofibrils
• STRATUM BASALE (basement layer)

  Cells

  Columnar keratinocyte cells

  Stem cells => site of EPIDERMAL CELLULAR PROLIFERATION

  Langerhans cells

  Merkel cells

  Melanocytes

  
  

  Cytoplasm

  Consists of melanosomes and keratin filament bundles (keratin tonofilaments)

  
  

  Desmosomes

  Connect plasma membranes of basal keratinocytes with each other (BETWEEN CELLS)

  
  

  Hemidesmosomes

  Anchor basal keratinocytes to the basement membrane  
• Basement membrane

  BC plasma membrane + Basal lamina (lamina lucida containing anchoring filament, lamina densa, dark)

  A) Basement membrane

  B) Dermis

  
• Epidermal pegs also called rete pegs contain stem cells

  
• DERMIS is MADE OF

  • Irregular, moderately dense CT
  • Meshwork of collagen (tensile strength) and elastin (stretch and recoil) fibres
  • Ground substance (glycosaminoglycans, glycoproteins & water)
• Dermis CONTAINS

  • fibroblasts (produce ECM), plasma cells, macrophages, blood vessels, nerves, lymphatics, epidermal appendages (hair, sweat glands and sebaceous glands)
• DERMIS REGIONS (superior to inferior):

  Papillary

  
  

  Reticular

  
• Papillary layer

  Immediately next to the epidermis

  Can find rete ridges which interdigitate with rete pegs

  Predominantly consist of Collagen type Ill and some elastic fibres

  Fine and loosely packed collagens

  Sensory receptors (Meissner's corpuscles)
• Reticular layer

  No proper boundary between papillary and reticular laver

  Collagen type Il with some elastin fibbers fibres

  Thick, irregular bundles of collagen

  Sensory receptors (Pacinian corpuscles)

  =>Also present in hypodermis
• HYPODERMIS

  Layer of CT of variable thickness, deeper to dermis

  Mainly consist of adipose tissue

  Blood vessels (BV), nerves & lymphatic travels trough it 
• Hypodermis FUNCTION

  Increase mobility of the skin

  Adipose

  • Thermal insulation
  • Shock absorber
  • Store metabolic energy
• ACCESORY STRUCTURES / EPIDERMAL DERIVATIVES

  HAIR - Sensory and thermoregulation - has arrector pili muscle

  SEBACEOUS GLANDS  –Produce sebum, epidermal barrier - associated with hair follicle - sebum lubricates

  SWEAT GLANDS (apocrine & eccrine/everywhere) - thermoregulation

  
• SWEAT GLANDS

  Eccrine

  Secretions from the secretory cells will be passed to the eccrine duct

  Duct is deeply stained (darker bc more organelles, lots of mt & modify sweat composition)

  
• SENSORY RECEPTORS

  • Touch
  • Pressure
  • Temperature
  • Pain
• TACTILE (MEISSNER) CORPUSCLES

  Encapsulated (Corpuscle)Rapidly adoptive mechanoreceptor

  LOCATION:

  Dermal papillae

  FUNCTION:Sensitive to touch

  
• LAMELLAR (PACINIAN) CORPUSCLES

  Encapsulated (Corpuscle)

  Has an intermediate zone

  Has a central core (contains an axon terminal)- Rapidly adapting mechanoreceptors

  LOCATION:Reticular dermis and hypodermis

  FUNCTION:Sensitive to pressure and vibration