integument B

Overview of Skin and Integument

  • Integument: The skin, as the largest organ of the body, serves as a barrier against external threats and retains bodily fluids.

Learning Objectives

  • Describe the layers of the epidermis and the cells in each layer.

  • Examine the dermis.

  • Explain the keratinization process of epidermal growth.

  • Refer to Saladin’s 8th edition, section 6.2, "The Skin and Subcutaneous Tissue," pages 160 to 166.

Skin Structure

Layers of the Skin

  • Epidermis: The superficial layer.

  • Dermis: The deeper layer beneath the epidermis.

  • Hypodermis: The layer beneath the dermis.

Epidermis Histology

  • Composed primarily of tightly packed epithelial tissue, enhancing its barrier function.

  • Dermal Papillae: Projections from the dermis that interdigitate with the epidermis, increasing the surface area for better adhesion.

Layers of the Epidermis

Stratum Basale (Basal Layer)

  • Type of Cells:

    • Keratinocytes: Predominant cell type, producing keratin.

    • Melanocytes: Produce melanin, provide pigmentation.

      • Melanocytes send projections with melanin granules that keratinocytes engulf, protecting them from UV radiation.

    • Merkel Cells (Tactile Cells): Function as touch receptors in association with nerve endings.

Stratum Spinosum (Spiny Layer)

  • Mostly keratinocytes.

  • Contains Langerhans Cells (immune cells) that detect and respond to pathogens.

  • Appearance is spiny due to prominent desmosomes (cell junctions).

Stratum Granulosum (Granular Layer)

  • Represents the transition between living and dead cells.

  • Cells are flatter, nuclei are less visible; characterized by the presence of granules:

    • Lipid Granules: Provide waterproof barrier by filling spaces between cells.

    • Keratohyalin Granules: Serve as precursors for keratin bundles to establish a strong barrier.

Stratum Corneum (Horny Layer)

  • Composed of dead keratinocytes that are flattened and filled with keratin.

  • Functions as a protective barrier, with no nuclei present.

Keratinization Process

  • Only the cells in the stratum basale undergo mitosis. As new cells are produced, they move up through the epidermal layers, losing nutrients and undergoing keratinization until they die and become part of the stratum corneum.

Dermis Structure

  • Composition: Dense irregular connective tissue, provides strength and elasticity; also contains a thin layer of areolar connective tissue.

  • Contains various structures:

    • Hair Follicles: Associated with nerve endings, acting as sensory receptors.

    • Receptors:

      • Pacinian Corpuscles: Detect deep pressure and vibration.

      • Meissner’s Corpuscles: Detect light touch and low-frequency vibrations.

    • Free Nerve Endings: Responsible for pain and temperature sensations.

    • Glands:

      • Sebaceous Glands: Associated with hair follicles, secrete oil.

      • Sweat Glands (Sudoriferous Glands): Found directly on the skin or associated with hair follicles.

  • The dermis provides the structural integrity of the skin and is utilized in making leather.

Visuals and Images

  • Various illustrations show the structure and differences in epidermal and dermal layers, highlighting features like the stratum lucidum (present in thick skin) and the arrangement of collagen fibers in the dermis.

Conclusion

  • Understanding the layers and cell types of the skin is crucial for recognizing how the skin serves as a protective barrier and engages in sensory functions. Further exploration of skin appendages like hair and nails will be covered in the next session.