Skin Anatomy and Functions

Skin - An External Body Covering

• The skin is the body's largest organ, an external covering, it is a pliable yet tough membrane.
• It is exposed to air and is a dry membrane, which helps keep water and other important molecules in the body, but also keeps water out.

Skin Functions

• Protection:

  • Protects deeper tissues from mechanical damage, due to keratin and pressure receptors.
  • Protects deeper tissues from chemical damage, the keratinized cells of the skin are relatively impermeable to foreign substances, pain receptors alert the body to potential harm.
  • Protects deeper tissues from bacterial damage, skin secretions are acidic, inhibiting bacteria and the skin provides an unbroken surface. Phagocytes within the skin ingest foreign pathogens, preventing them from penetrating deeper tissues.
  • Protects deeper tissues from ultraviolet radiation (damaging effects of sunlight) melanin produced by melanocytes offers protection from UV damage.
  • Protects deeper tissues from thermal damage, heat/cold/pain receptors respond to changes in the environment that can damage the skin.
  • Protects against desiccation (drying out), a waterproofing glycolipid and the keratin found in skin prevent this.

• Regulation:

  • Aids in body heat loss or heat retention, sweat glands are activated and blood flushes into skin capillary beds when hot, allowing for heat loss. The reverse occurs to retain heat.

• Excretion:

  • Aids in the excretion of urea and uric acid, contained within perspiration secreted by the sweat glands.

• Synthesis:

  • Synthesizes vitamin D, sunlight acts on modified cholesterol molecules in the skin, converting them to vitamin D.

Skin Structure

• Epidermis:

  • The outermost layer of skin.
  • Composed of several layers:
    • Stratum basale: The deepest layer of the epidermis, lies closest to the dermis, where epidermal cells receive nutrients. Cells here are undergoing continuous cell division.
    • Stratum spinosum and stratum granulosum: Daughter cells from the stratum basale are pushed upwards to form these layers.
    • Stratum lucidum: Cells in these layers become flattened, filled with keratin and eventually die.
    • Stratum corneum: The outermost layer of the epidermis, composed of dead, keratinized cells.

• Dermis:

  • The middle layer of skin, containing blood vessels, nerves, glands, and hair follicles.

• Hypodermis: (also called subcutaneous layer)

  • The deepest layer of skin, is essentially adipose tissue.
  • Anchors the skin to underlying organs.
  • Acts as a shock absorber.
  • Insulates the deeper tissues from extreme temperature changes.