Integument (Skin)

Learning Objectives

  • Identify tissues in epidermis and dermis.
  • Describe hypodermis structure and function.
  • Define four principal cell types of epidermis:
    • Keratinocytes, melanocytes, Langerhans cells, Merkel cells.
  • Understand epidermal cell layers' organization.
  • Compare papillary and reticular dermis composition.
  • Explain elastic and collagen fibers' significance in dermis.

Structure of the Integument

  • Composed of:
    • Superficial epidermis
    • Deeper dermis
    • Accessory structures (hair follicles, exocrine glands, nails)

Functions of the Skin

  1. Regulates body temperature.
  2. Protects underlying tissues from external environment.
  3. Detects sensations (touch, pain, temperature).
  4. Excretes substances (salts, water, organic wastes).
  5. Synthesizes vitamin D.

Layers of the Skin

Epidermis
  • Comprised of four or five layers:
    1. Stratum basale
    2. Stratum spinosum
    3. Stratum granulosum
    4. Stratum lucidum (only in thick skin)
    5. Stratum corneum
Dermis
  • Two main layers:
    • Papillary layer
    • Reticular layer
Hypodermis
  • Subcutaneous tissue; mainly adipose connective tissue.
  • Functions: energy storage, thermal insulation.

Principal Cell Types in Epidermis

  • Keratinocytes: predominant, produce keratin for protection.
  • Melanocytes: synthesize melanin for UV protection.
  • Merkel Cells: detect touch sensations.
  • Langerhans Cells: phagocytic, immune response.

Stratum Layers Description

  1. Stratum Basale: Deepest layer, active mitosis, contains stem cells.
  2. Stratum Spinosum: Thick layer with spiny keratinocytes, resists tension.
  3. Stratum Granulosum: Cells begin keratinization; contains glycolipid granules.
  4. Stratum Lucidum: Only in thick skin, clear and dead keratinocytes.
  5. Stratum Corneum: Outermost layer, dead keratinized cells, functions as barrier.