Integument

Overview of Integumentary System

  • The integument, or outer skin, consists of three principal layers:

    • Epidermis: The outermost layer.

    • Dermis: The middle layer.

    • Hypodermis (subcutaneous layer): The deepest layer, also known as the hypodermis.

Structure of Skin Layers

Epidermis

  • Comprised of keratinized stratified squamous epithelium.

  • Avascular: Lacks blood vessels, receiving nutrients through diffusion from the dermis.

  • Contains keratinocytes (main cell type), melanocytes (pigment-producing cells), and tactile cells (sensory receptors).

  • Has five distinct layers:

    1. Stratum Basale

      • Basal layer with stem cells and mitotic activity.

      • Contains keratinocytes, melanocytes, and tactile cells.

    2. Stratum Spinosum

      • Several layers thick, some mitotic activity.

      • Home to epidermal dendritic cells (immune response).

    3. Stratum Granulosum

      • Beginning of keratinization; cells lose organelles and nuclei.

      • Transition layer between living and dead cells.

    4. Stratum Lucidum (optional in thin skin)

      • Present in thick skin (hands/feet); a few layers thick.

    5. Stratum Corneum

      • Outermost layer, composed of dead, anucleated keratinized cells.

      • Cells here shed regularly (dust).

Dermis

  • Comprised of dense irregular connective tissue.

    • Has two major layers:

      1. Papillary Layer

        • Composed of areolar connective tissue.

        • Houses capillary beds and sensory neurons.

      2. Reticular Layer

        • Thicker layer made of dense irregular connective tissue.

        • Contains accessory structures (glands, hair follicles).

  • Features lines of cleavage (collagen and elastic fiber orientation)

    • Important for surgical incisions to minimize scarring.

Hypodermis

  • Also known as the subcutaneous layer.

  • Composed mainly of adipose and areolar connective tissue.

  • Functions as insulation and energy storage, anchors integument to underlying structures.

Functions of Skin

  • Protection: Acts as a barrier against pathogens, chemicals, and physical damage.

  • Regulation: Aids in thermoregulation and sensation (touch, pressure, pain).

  • Sensation: Contains nerve endings for detecting external stimuli.

  • Water resistance: Keratin in epidermal cells aids in preventing water loss.

Glands in the Skin

Sebaceous Glands

  • Produce oil (sebum) that helps waterproof and lubricate the skin.

Sweat Glands (Two Types)

  1. Merocrine Glands

    • Location: Distributed throughout the body, especially on palms, soles, and forehead.

    • Function: Primarily involved in thermoregulation.

  2. Apocrine Glands

    • Location: Found mainly in axillary (armpit) and genital areas.

    • Function: Secretes thicker fluid into hair follicles; associated with body odor.

Unique Skin Features

  • Friction Ridges (Fingerprints): Enhance grip and tactile feedback.

  • Wrinkling in Water: Initially thought to be osmotic but is now understood to be a sympathetic nervous response increasing gripping ability.

Summary of Skin Anatomy and Function

  • Skin is a complex organ composed of multiple layers with specialized cells and structures, each contributing to its overall function of protection, regulation, and sensation.

  • The interplay between the different skin layers allows for efficient communication, nutrient supply, and responsiveness to the environment.