Week 4 LR4 Integumentary (Dermis, hypodermis)

Overview of the Dermis

  • The dermis is the main portion of the skin, thicker than the epidermis, and varies in thickness across different body areas.

  • Thickest at the back, leading to surgical difficulties and keloid formation.

Structure of the Dermis

  • Composed of strong, flexible connective tissue mostly made up of collagen (triple helix structure).

  • Collagen is stronger than keratin and is stabilized by hydrogen bonds, which require Vitamin C for formation.

Functions of the Dermis

  • Transdermal Drug Delivery:

    • Allows medications to pass through via lipid solubility.

    • Common examples include nicotine patches, hormone replacement therapy, and nitroglycerin for heart issues.

    • Important to wear gloves when applying due to transference through skin.

  • Thermoregulation:

    • Regulates blood flow to maintain body temperature via vasoconstriction (reducing blood flow to skin) and vasodilation (increasing blood flow to skin).

    • Hypothalamus acts as the body's thermostat, responding to peripheral thermoreceptors.

Layers of the Dermis

  • Papillary Layer:

    • Loose connective tissue beneath the epidermis.

    • Contains dermal papillae that interlock with the epidermis, providing structural stability and enhancing grip.

    • Houses blood vessels, leukocytes, nerves, and plays a role in sensation.

  • Reticular Layer:

    • Composed of dense irregular connective tissue, making up 80% of skin thickness.

    • Contains collagen and elastic fibers arranged in bundles to resist various tensions and stresses.

    • Housing fibroblasts and macrophages for tissue maintenance and repair.

    • Laminated Corpuscles detect pressure and create awareness of stimuli.

Healing and Surgical Considerations

  • Cleavage Lines:

    • Arrangement of collagen fibers allows for strategic cutting to minimize scar tissue.

    • Plastic surgeons cut along these lines for optimal healing results.

Hypodermis (Subcutaneous Layer)

  • Contains loose connective tissue and adipocytes, storing 50% of body fat.

  • Acts as a shock absorber and insulator, maintaining body temperature at 37°C.

  • Important for slow absorption of medications given through subcutaneous injections (e.g., insulin, heparin) due to lack of pain receptors.

Cellular Composition of the Dermis

  • Major cells found include:

    • Fibroblasts: Produce collagen fibers.

    • Macrophages: Clean up debris and pathogens.

    • Dendritic Cells and Melanocytes: Primarily found in the epidermis but important for skin health.