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Friday, October 12, 2007

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


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)



  • 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


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>


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


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


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>

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