Physiology -Chap 5- Outline

Structure of the Skin

Largest organ in the body

• Skin (Cutaneous membrane)
  
  • Largest organ in both size and weight
    
  • Has two main parts
    
    • Epidermis
      
      • Thinner
        
      • Composed of epithelial tissue
        
      • Kerantinized stratified squamous epi.
        
      • Four cells types
        
        • Keratinocytes
          
          • Arranged in four or five layers
            
          • Produce keratin
            
          • Produce lamellar granules: release water repellent sealant
            
        • Meloanocytes
          
          • Develop from ectoderm
            
          • Produce melanin
            
            • Yellow-red or brown-black pigment that contributes to skin color
              
        • Langerhans
          
          • From red bone marrow and move to epi.
            
          • Immune responses
            
        • Merkel
          
          • Contact flattened process of sensory neuron (tactile disc)
            
      • Four strata, or layers in most places (thin skin)
        
        • Stratum basale
          
        • Stratum spinosum
          
        • Stratum granulosum
          
        • Stratum corneum-thin
          
      • Five layers in certain places (thick skin)
        
        • Stratum basale
          
        • Stratum spinosum
          
        • Stratum granulosum
          
        • Stratum Lucidum
          
        • Stratum corneum-thick
          
    • Dermis
      
      • Deeper and thicker
        
      • Connective tissue
        
• Subcateous layer (hypodermis)
  
  • Consists of Areolar and adipose tissue
    
  • Fibers connect hypodermis to dermis which attaches to organs
    
  • Storage for fat and contains large blood vessels
    
  • Contains llamellated corpuscles
    
    • Nerve endings sensitive to pressure
      
• 
  
• Stratum Basale
  
• Deepest Layer
  
• Single row cuboidal or columnar keratinocytes
  
• Some cells in this layer are stem cells
  
• Cytoskeleton of kera. Include tonofilaments
  
  • Composed of protein that forms keratin in more superficial layers
    
  • Attech to desmosomes
    
• Also known as stratum germination
  

  
  

Stratum Spinosum

Many-sided kera. Fill 8-10 layers

• When prepared for examination kera. pull apart, form thorn-like points, and shrink
  
• When in living tissue they are rounded and larger
  
• Add strength and flexibility to skin
  

Stratum Granulosum

3-5 layers of flattened kera.

• Kera. is undergoing apoptosis
  
• Other organelles degenerate
  
• Tonofilaments become more apparent
  
• Contains keratohyalin
  
  • Protein that converts tonofilaments into keratin
    
• Contains lamellar granules
  
  • Releases lipid-rich secretion
    
    • Fills spaces between cells
      
    • Water-repellant sealant
      

Statum Lucidum

Three to five layers of flattened, clear, dead, kera.

• Only in thick skin
  
• Large amounts of kertin, and thickened plasma mem.
  

  
  

  Stratum Corneum
  

  25-30 layers of flattened dead kera.
  

• Continuously shed and replaced
  
• Interiors contains mostly keratin
  
• Many layers of dead cells protect deeper levels from injury
  
• Contant exposure to friction cause callus
  

Keratinization and Growth of the Epidermis

• Keratinization
  
  • Cells formed in basale pushed to surface
    
    • As they move through each layer they obtain more keratin –Keratinization
      
• Then they go through apoptosis
  
• Takes four weeks
  
• Hormone-like proteins play role in epi. regeneration
  
  • Epidermal growth factor
    

Dermis

Second part of skin

• Blood vessels, nerves, glands, and fair follicle embedded
  
• Divided into two parts
  
  • Papillary region
    
    • 1/5 of total layer
      
    • Areolar CT
      
    • Surface area increased by dermal papillae
      
      • Nipple-shaped
        
      • Contain capillary loops, tactile receptors called corpuscles of touch, nerve endings, and free nerve ending
        
  • Reticular region
    
    • Attached to subcutaneous layer
      
    • Contains dense irregular CT
      
    • Collagen & elastic fibers provide strength, extensibility, and elasticity
      
    • Extreme stretching may tear dermis, causing striae (stretch marks)
      

Notes

SKIN GAFTS

• New skin cannot regenerate if stratum basale is destroyed by an injury
  
• To heal skin you need a skin gaft
  
  • Patch of healthy skin, taken from a donor site
    

VOCAB.

Cutaneous Membrane: Skin

Epidermis: Thinner layer of skin, composed of E. T.

Dermis: Thicker layer of skin, composed of C.T.

Subcutaneous Layer: Hypodermis, connects to dermis on one side & organs on other

Hypodermis: Subcataneous layer

Lamallated Corpuscles: Nerve endings sensitive to pressure

Keratinocytes: Majority of epi. cells. Produce keratin

Keratin: Protien produced by keratinocytes

Melancytes: Develop frm ectoderm. Produce melanin

Melanin: Givves skin pigment

Langerhans Cells: Ceom frm. Red-bone marrow and move to epi. Immune system responses

Merkel Cells: Contact tactile disc

Tactile Disc: Flattened process of sensory nueron

Thin Skin: Has only the four layers (basale, spinosum, granulosum, & corneum)

Thick Skin: Five layers (basale, spinosum, granulosum, lucidum & corneum)

Startum Basale: Layer number one of skin

Skin Graft: Healthy skin from a donas

Stratum Spinosum: Layer number two of skin

Stratum Granulosum: Layer number three of skin

Keratohyalin: Protein, convert tonofilaments to keratin

Lamellar Granules: Release lipid-rich secretion

Stratum Lucidum: Optional layer number four

Stratum Corneum: Layer number four/five

Keratinization: Process of cells moving from basale through other layers, picking up karatin

Epidermal Growth Factor: Hormone-like protein

Papillary Region: One region of dermis

Dermal Papillae: Increases surface area of papillary region

Capillary Loops: Blood capillaries

Corpuscles of Touch: Tactile receptors

Free Nerve Endings: Dendrites that lack structural specialization

Reticular Region: One region of dermis

Striae: Stretch marks

Lines of cleavage: Indicate predominant direction of underlying collagen fibers

Epidermal Ridges: Grooves in places as fingers and palms

Pasted from <file:///C:\Users\Joyce\Documents\School\Physiology\physio.%20145-150.docx>

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The Structural Basis of Skin Color

Melanin, hemogoblin, and carotene=Skin pigments

• Melanin: skin color from pale to black
  
  • Pheomelanin (yellow to red) =] Difference is
    
  • Eumelanin (brown to black) =] in the hair
    
  • Melanocytes are more in the epi. of penis, nipples of breasts, face, and limbs
    
  • Difference in skin color caused by pigments the melanocytes produce
    
  • Synthesied from tyrosine –occurs in melanosome
    
  • Melanin absorbs UV to protect DNA from being damaged
    
  • Light skinned people have little melanin, dark skinned people have more
    
• Carotine
  
  • Needed to synthesize for vision
    
• Albinism
  
  • Inherited inability to produce melanin.
    

Tattooing and Body Piercing

• Tattooing
  
  • Needle with foreign pigment is inserted into dermis
    
• Body Piercing
  
  • Insertion of jewelry into an artificial hole
    

Accessory Structures of the Skin

Hair, skin, glands, and nails

• Develop from embryonic epidermis
  

  Hair
  

Present on most surfaces

• Hair guards scalp from injury
  
• Eyebrows and eyelashes protect eyes
  
• Touch receptors associated with hair follicles activated at the slightest touch
  

Anatomy of a Hair

• Composer of dead, keratinized cells bonded together by E-C proteins
  
• Shaft is the superficial portion which projects from skin
  
• Root is the portion of hair deep to the shaft
  
  • Shaft and root of hair have three concentric layers
    
    • Medulla, cortex, and cuticle
      
      • Medulla: composed of two or three rows of irregularly shaped cells
        
      • Cortex: forms major part of shaft and consists of elongated cells
        
      • Cuticle: outermost layer, single thin, flat cells
        
  • Surrounding root is the hair follicle
    
    • Made of external root sheath and internal root sheath –epithelial root sheath
      
    • Internal root sheath- produced by the matrix and forms a cellular tubular sheath of epithelium between the external root sheath and the hair
      

Hair Growth

• Growth stage
  
  • Cells of the matrix differentiate, keratinize, and die
    
  • In time the growth stops and cell enters resting stage
    

Vocab.

Melanin: Causes skin color to vary from pale yellow to red to tan to black

Nevus (mole): Round flat or raised area that is an overgrowth of melan.

Melanosome: Where the synthesis of melanin occurs

Hemogoblin: O2 carrying pigment in RBC

Carotine: Yellow-orange pigment that gives egg yolk and carrots their color

Albinism: Inherited inability to produce melanin, albinos

Vitiligo: Partial or complete loss of melo. From patches of skin

Shaft: The superficial portion which projects from skin

Root: Portion of hair deep to shaft

Epithelial Root Sheath: Downward continuation of epidermis

Dermal Root Sheath: Dense dermis surrounding the hair follicle

Bulb: Base of each hair follicle

Papilla of the Hair: Nipple shaped indentation in the bulb. Contains areolar CT

Pasted from <file:///C:\Users\Joyce\Documents\School\Physiology\physio.%20150-156.docx>