The Integumentary System

The Integumentary System: Layers of the Skin and Dermis

Layers of the Skin

• The skin is comprised of two major layers:

  • Epidermis: The outer, thinner layer, consisting of epithelial tissue.

  • Dermis: The inner, thicker layer, composed of connective tissue.

• Subcutaneous (subQ) Layer (Hypodermis):

  • Located beneath the dermis.

  • Composed of loose areolar and adipose connective tissue (C.T.).

  • Functions to attach the skin to underlying tissues and organs.

The Dermis

• Composition: Primarily connective tissue, rich in collagen and elastic fibers.

• Two Major Regions:

  • ### Papillary Region

    • Lies immediately beneath the epidermis.

    • Consists of areolar connective tissue.

    • Contains thin collagen and elastic fibers.

    • Features dermal papillae, which are finger-like projections that extend into the epidermis.

      • They contain capillary loops, providing nutrients to the avascular epidermis.

      • They house corpuscles of touch (Meissner corpuscles), responsible for light touch sensation.

      • Contains free nerve endings, detecting pain, temperature, itch, and tickle.

      • Papillary plexus (network of small blood vessels).

    • Epidermal ridges: These are surface manifestations reflecting the contours of the underlying dermal papillae.

      • They form the basis for fingerprints and footprints.

      • Their primary function is to increase friction, thereby enhancing the firmness of grip.

  • ### Reticular Region

    • The deeper and thicker part of the dermis.

    • Composed of dense irregular connective tissue.

    • Contains a dense arrangement of collagen and elastic fibers, providing strength and elasticity to the skin.

    • Includes adipose cells for insulation and energy storage.

    • Houses hair follicles, from which hairs grow.

    • Contains nerves for various sensations.

    • Contains sebaceous (oil) glands, which secrete sebum to lubricate skin and hair.

    • Contains sudoriferous (sweat) glands (both eccrine and apocrine), involved in thermoregulation and waste excretion.

    • Tears or excessive stretching of the collagen and elastic fibers in this region can lead to permanent damage, visible as stretch marks (striae).

  • ### Lines of Cleavage

    • Also known as "tension lines," these indicate the predominant direction of underlying collagen fibers in the dermis.

    • Knowledge of these lines is practically significant in surgery: plastic surgeons make incisions parallel to these normal cleavage lines to minimize scarring and promote faster healing.

The Subcutaneous Layer (Hypodermis)

• Serves as the attachment site for the skin to underlying tissues and organs.

• Contains:

  • Blood vessels (including cutaneous plexus, veins, and arteries) and nerves that are in transit to the more superficial layers of the skin.

  • Lamellated (pacinian) corpuscles, specialized sensory receptors that detect external pressure and vibration applied to the skin.