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2012-01-21 22:10:04
human physiology organ system

skin, lecture 5
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  1. Integument
    •Integument = Skin + its appendages (e.g., glands, hair nails and sensory receptors)

    •Largest organ of the body

    – ~22 square feet (1.5 – 2 m2)

    – ~10-11 pounds (4.5-5 kg; 7% body weight)

    –~ 1-2 mm (0.04-0.08 inch) thick

    •Two layers:



    –Epidermis and dermis are joined by dermal-epidermal junctions
  2. Subcutaneous layer(hypodermis/superficial fascia)
    –Loose connective tissue

    –Not a true part of integument

    –Attaches to connective tissue around muscles and bones
  3. Functions of Integument
    –Physical protection

    •Barrier against mechanical, chemical, and microbial factors that may affect the physiological status of the body







  4. Functions of Integument
    –Synthesized vitamin D3

    –Sensory information about the surrounding environment
  5. Epidermis
    •Composed of keratinized stratified squamous epithelium

    •Avascular tissue (no blood vessels)

    –Oxygen and nutrients diffuse from underlying dermis
  6. Four cell types
    –Keratinocytes (~90% of cells present)

    •The most abundant cells of the epidermis

    •Arranged in 4-5 layers

    •Produce keratin

    •Produce lamellar granules


    •Located in the stratum basale, the deepest layer of epidermis

    •Produce the brow pigment melanin

    •Filter UV radiation

    –Langerhans cells

    •Immune cells

    •Detect and destroy pathogens

    –Merkel cells

    •Located in the deepest layer of epidermis

    •Detect touch sensation
  7. Five distinct layers of epidermis
    –Stratum Basale (also known as Striatum Germanitivum)

    –Stratum Spinosum

    –Stratum Granulosum

    –Stratum Lucidum

    •Only present in thick skin (e.g. fingertips)

    –Stratum Corneum

    •Thin skin- thin stratum corneum

    Thick skin- thick stratum corneum
  8. Stratum Basale
    –Deepest layer of epidermis

    •between epidermis and dermis

    –Consist of single layer of columnar or cuboidal Keratinocytes, which rest on the basement membrane

    –Contains stem cells which continuously give rise to a new keratinocytes

    • •In human the renewal of epidermis takes ~
    • 3-4 weeks

    –Form epidermal ridges, dermal pappilae

    –Contains Melanocytes and Markel cells
  9. Stratum Granulosum (granular layer) and Stratum Spinosum (spiny layer)
    •Stratum Spinosum (spiny layer)

    –Composed of 8-10 layers of keratinocytes

    –Contains the highest concentration of Langrehan’s cells and projections of melanocytes

    •Stratum Granulosum (granular layer)

    –Cells arranged into 2-5 layers


    –Contain lamellar granules within the keratinocytes

    •Release lipid-rich secretions

    –Water repellent
  10. Stratum Corneum (horny layer) and Stratum Lucidum (clear layer)
    •Stratum Corneum (horny layer)

    –Protective layer of epidermis

    –Keratinized layer of cells (~ 30 cells thick)

    –Cells are flat; space between cells filled with lipids

    –Cells continuously shed and are replaced from deeper strata

    •Stratum Lucidum (clear layer)

    –Present only in thick skin

    •Skin on the fingertips, palms and soles

    •4-6 layers of flat, dead keratinocytes
  11. Skin Color
    •Skin color results from the combination of genetic, physiological and environmental factors


    –An oxygen-binding protein present in red blood cells

    –Bright red color

    • Melanin

    –Pigment produced and stored in melanocytes

    •Eumelanin- group of dark-brown melanins

    •Pheomelanin- group of reddish and orange melanins

    –Differences in skin color results from the different amounts of melanin
  12. b-Carotenes

    •High consumption of carrot/carrot juice or sweet potato may cause orange or yellow coloration of the skin
  13. Dermis
    •Dense connective tissue with numerous collagenous and elastic fibres

    •Contains the following:

    –Blood supply

    •Critical for temperature regulation

    –Nerve supply

    •Sensory receptors for pain, pressure, touch and temperature

    Hair and nails

    Extracellular matrix is a complex structure composed of highly organized collagen, elastic, and reticular fibers. Collagen provides the skin with tensile strength and tissue integrity whereas elastin provides elasticity and resiliency

    Contains macrophages and mast cells, as well as glands. Sebaceous glands secrete triglyceride and cholesterol-rich sebum that lubricate the skin and keep it supple and waterproof
  14. Two major regions of dermis
    •Superficial pappilary layer

    –1/5th of the thickness of the total dermis

    –Contains fine collagenous and elastic fibers

    –Contains the dermal-epidermal junctions

    –Contain corpuscle of touch (Meissner corpuscle)

    – Contain free nerve endings

    •Pain, warmth, coolness, itching

    •Deeper reticular layer

    –Contains collagen and elastic fibers, adipose tissue, hair follicles and glands

    –Provides the skin with extensibility and elasticity

    –Stretch marks

    •Tears in dermis that result from extreme streching
  15. Epidermal ridges
    –Downward projections of the epidermis and dermis

    –Present on the surfaces of palms, fingers and toes

    –Epidermal ridge pattern –basis for identification through fingerprints or footprints
  16. Appendages of the Skin

    –Sudoriferous (sweat) glands

    –Sebaceous (oil) gland



  17. Sudoriferous (Sweat) Glands
    –Most numerous glands of the skin

    –Excrete sweat from the skin

    –Classified into two groups:

    •Eccrine sweat glands

    –Found only in primates

    –Most numerous in the skin of palms, soles and forehead

    • –Regulate body temperature and help to eliminate waste
    • products

    •Apocrine sweat glands

    • –Found in the skin of the armpit, groin, pigmented area
    • around nipples

    –Secretory portion located in hypodermis
  18. Sebaceous glands
    –Classified as holocrine glands

    •Sebum released as cells burst

    • –Produce sebum (oil) that contains cholesterol,
    • triglycerides, proteins and inorganic salts

    •Keeps the hair supple and skin soft and pliant

    –Found in dermis (except palms and soles)

    –Connected to the hair follicles

    •Prevents excessive water loss from the skin

    Sebum contains 45% water-insoluble fatty acids known to have broad antimicrobial activity. Also sebum provides Vitamin E to the upper layers of facial skin. Sebaceous lipids contribute to maintain integrity of skin barrier, and express pro-inflammatory and anti-inflammatory properties

    People who develop hormonal acne have over stimulated sebaceous glands
  19. Ceruminous Glands
    –Simple, coiled tubular glands

    •3-4 millions

    –Modified apocrine sweat glands

    –Found in external ear canal or with sebaceous glands

    –Mix secretion of sebaceous and ceruminous glands produce cerumen (a brown waxy substance)
  20. Hair (Pili)
    –Can be found over entire regions of the skin, except palms of hands and soles of feet

    • –Hair color is
    • determined by the amount of type melanin present

    •Variation in hair color is due to the genetically determined differences in the structure of the melanin

    –Function of Hair:


    •Heat retention

    •Sensory reception

    • Visual identification
  21. Hair

    •Superficial portion of the hair

    •Straight hair-round in transverse section

    •Curly hair- kidney shaped in transverse section


    •Penetrates into dermis

    • •Both, shaft and root, are composed of three concentric
    • layers:

    –Inner medulla

    »Pigment granules in dark hair

    »Air bubbles in white hair

    –Middle cortex

    »Elongated cells


    Single layer of heavily keratinized cells

    –Hair Follicle

    •Surrounds the root of the hair

    •Surrounded by the dermal root sheet

    –Dense dermis

    –Hair Matrix

    •Contains cells that divide

    –Hair Growth

    • •Growth stage (2-6 years),regression stage (2-3 weeks)
    • and resting stage (3 months)

    –Hair Color

    •Determined by the type and amount of melanin produced
  22. Nail
    –Protective covering over the ends of fingers and toes

    –Composed of stratified squamous keratinized epithelial cells overlying the nail bed
  23. Appendages of Skin- Nails
    •Nail body

    –Visible part of each nail


    –Buried in fold of skin


    –Moon-shaped white area nearest root

    –Site of nail growth

    •Nail bed

    –Layer of epithelium under nail body

    –Contains abundant blood vessels
  24. Skin Coloration
    •Freckles and moles

    –Melanin becomes concentrated in a specific area


    –Melanocytes do not secrete melanin

    –Hair, skin and iris are white


    –Skin appears blue due to the poorly oxygenated blood


    –Results from the dilation of blood vessels
  25. Thermoregulation
    –Homeostatic regulation of body temperature

    –High environmental temperature OR sweating

    •↑ sweat production by eccrine sweat glands

    •Dilation of the blood vessels in the dermis→ increased amount of blood flow→ increased heat loss

    –Low environmental temperature

    •↓production of sweat

    •Blood vessels constrict → decreased heat loss
  26. Blood reservoir and protection
    •Blood Reservoir

    –Dermis has an extensive network of blood vessels

    •8-10% of total blood flow



    –Lipids released from lamellar granules

    •Protects the skin from dehydration

    •Prevent water entry from environment

    –Sebum from the sebaceous glands

    •Keeps skin and hair from drying out

    •Bactericidal chemicals-kill bacteria


    •Protection against ultraviolet radiation

    –Langreham Cells

    • Alert the immune system
  27. Cutaneous Sensations
    –Tactile Sensations

    •Touch, pressure, vibration and tickeling

    –Thermal Sensation

    •Warmth and cosolenes

  28. Exertion and absorption and synthesis of vitamin D
    •Exertion and Absorption


    • •Water, small amounts of salts, carbon dioxide, ammonia
    • and urea


    •Certain drugs and toxins

    •Synthesis of Vitamin D

    –UV rays activate precursor molecule in the skin, which then is modified in kidney and liver to form calcitriol (active form of vitamin D)
  29. Tattooing and Body Piercing

    –Originated in ancient Egypt (4000-2000 B.C.)

    –Permanent coloration of the skin

    –Ink is injected with a needle into the dermis

    •Body Piercing

    –Employed by Egyptian pharaohs and Roman soldiers

    –Insertion of jewellery through an artificial opening