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��General Anatomy� Skin ����

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  • Skin (integument) is body’s largest organ.
  • Integumentary system describes the skin �and its appendages—the hair, nails, and �skin glands.

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Anatomy of Skin

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Functions of Skin

Functions of the Integumentary System:

    • First defensive barrier of immune response (physical barrier).
    • Protection from dehydration, infection & UV rays.
    • Regulation of body temperature.
    • Respond to different sensations e.g., temperature, pressure, pain, touch, … etc
    • Excretion of water, salts, urea (nitrogenous waste).
    • Synthesis of vitamin D (essential for Ca + P absorption).

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Layers of Skin

  1. Epidermis
  2. Dermis

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N.B. Subcutaneous layer:

    • beneath dermis
    • not part of skin

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Epidermis

  • Keratinized stratified squamous epithelium.
  • Rests on a basement membrane separating it from the dermis.
  • Lacks blood vessels.
  • Thickest on palms and soles (0.8-1.4mm).

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Cells of the Epidermis

  • Keratinocytes: constitute over 90% of cells present; principal structural element of the epidermis.
  • Melanocytes: melanin-producing cells (5% of the total); contribute to skin color; filter ultraviolet light.
  • Langerhans cells: dendritic (branched) antigen-presenting cells (APCs), they play a role in adaptive immune response.

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Layers of the Epidermis

From superficial to deep:

    • Stratum corneum: dead cells filled with keratin.
    • Stratum lucidum: present only in thick skin.
    • Stratum granulosum.
    • Stratum spinosum: the thickest layer of the skin.
    • Stratum basale: single layer of columnar cells resting on a basement membrane.

N.B. Stratum germinativum (growth layer): describes the deep cells of stratum spinosum and stratum basale together that divide actively to replace cells of top layers.

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Dermis

  • Dense irregular connective tissue.
  • Contains dermal papillae.
  • Binds epidermis to underlying tissues.
  • Contains blood vessels, muscle cells, nerve cell processes, sensory receptors, hair follicles & glands.

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Layers of the Dermis

  1. Papillary layer: composed of dermal papillae that project into the epidermis; a loose connective tissue layer; contains the dermal-epidermal junction; forms a unique pattern that gives individual fingerprints.
  2. Reticular layer: contains dense, interlacing white collagen fibers and elastic fibers to make the skin tough yet stretchable.

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Lines of Cleavage

  • Tension lines in the skin identify the predominant orientation of collagen fiber bundles.
  • Clinically and surgically significant because cuts perpendicular to these lines can result in slow healing and increased scarring.

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Subcutaneous Layer

  • Hypodermis/ Subcutis/ Superficial fascia.
  • Loose connective tissue + adipose tissue.
  • Acts as a thermal insulator.
  • Contains major blood vessels.

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Skin Color

Genetic factors

    • Varying amounts of melanin
    • Varying size of melanin granules
    • Albinos lack melanin

Environmental factors

    • Sunlight
    • UV light from sunlamps
    • X rays
    • All darken melanin

Physiological factors

    • Dilation of dermal blood vessels
    • Constriction of dermal blood vessels
    • Accumulation of carotene
    • Jaundice

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Sebaceous glands

      • Secrete sebum—oily substance that keeps hair and skin soft and pliant; prevents excessive water loss from the skin
      • usually associated with hair follicles
      • Lipid components have antifungal activity
      • Found in dermis except in palms and soles
      • Secretion increases in adolescence; may lead to formation of pimples and blackheads (Acne Vulgaris)

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Skin glands

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Sweat Glands

  • Widespread in the skin.
  • Originates in deeper dermis or hypodermis.
  • Types of sweat glands:
    1. Eccrine glands: widely distributed; important in sweating & temperature regulation.
    2. Apocrine glands: limited to the axilla, perianal region & areola of the breast. They function at puberty.
    3. Modified sweat glands:
      1. Ceruminous glands: secrete ear wax.
      2. Mammary glands: secrete milk.

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Sweat Glands

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Hair

  • Distribution: over the entire body except palms of hands, soles of feet and a few other small areas
      • Fine and soft hair present before birth is called lanugo.
      • Coarse pubic and axillary hair that develops at puberty is called terminal hair

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Hair Thinning and Baldness

  • Alopecia – hair thinning in both sexes
  • True, or frank, baldness
    • Genetically determined and sex-influenced condition

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    • Consist of epidermal cells converted to hard keratin
    • Nail body—visible part of each nail
    • Root—part of nail in groove hidden by fold of skin, the cuticle
    • Lunula—moon-shaped white area nearest root

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Nails

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Burns

  • Tissue damage from excessive heat, electricity, radioactivity, or corrosive chemicals that destroys (denatures) proteins in the exposed cells is called a burn.

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  • Generally, the systemic effects of a burn are a greater threat to life than are the local effects.

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  • The seriousness of a burn is determined by
    • Its depth
    • Extent
    • Area involved
    • The person’s age and general health.

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  • When the burn area exceeds 70%, over half of the victims die

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Burns

  • Problems that result from burns:
    • Shock due to water, plasma and plasma protein loss.
    • Circulatory & kidney problems from loss of plasma.
    • Bacterial infection.

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Types of Burns

  • First-degree
    • only epidermis (sunburn)

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Types of Burns

  • Second-degree burn
    • destroys entire epidermis & part of dermis
    • fluid-filled blisters separate epidermis & dermis
    • epidermal derivatives are not damaged
    • heals without grafting in 3 to 4 weeks & may scar

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Types of Burns

  • Third-degree or full-thickness
    • destroy epidermis, dermis & epidermal derivatives
    • damaged area is numb due to loss of sensory nerves

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Rule of Nines

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Skin Cancer

  • The most common type of cancer.
  • The greatest risk factor is exposure to UV rays of the sun.
  • The highest incidence is in people who have had severe sunburns, especially as children.

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Skin Cancer

  • Most skin tumors are benign and do not metastasize.
  • The three major types of skin cancer are:
    • Basal cell carcinoma (most common)
    • Squamous cell carcinoma
    • Melanoma (most dangerous)

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Basal Cell Carcinoma

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Squamous Cell Carcinoma

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Malignant Melanoma

  • Cancer of melanocytes is the most dangerous type of skin cancer because it is:
    • Highly metastatic
    • Resistant to chemotherapy

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Malignant Melanoma

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THE END