5-2 The Dermis Layer

The dermis is the supportive tissue layer located between the epidermis and the subcutaneous layer.

The dermis contains:
- Accessory structures of epidermal origin (e.g., hair follicles, sweat glands)
- Networks of blood vessels and nerve fibers

Composition: Made up of areolar tissue.
Components: Contains capillaries, lymphatic vessels, and sensory nerve fibers that supply the surface of the skin.
Function: Provides nutrients and sensory functions.
Dermal papillae:
- Projections that extend between the epidermal ridges (see Figure 5.3a).
- They increase the surface area for exchange between the dermis and epidermis.
Sensory Function:
- Abundant sensory nerve endings and receptors make the area sensitive to touch and pain.
- Regional inflammation (dermatitis) can cause pain, particularly in the papillary layer.

Composition: Made of dense irregular connective tissue.
Components: Contains collagen and elastic fibers.
- Collagen fibers extend into both the papillary layer and deeper subcutaneous layer.
- This meshwork provides strength and elasticity.
Function: Provides structural support and elasticity to the skin.

Strength and Elasticity:
- Collagen Fibers: Strong and resist stretching, easily bent or twisted.
- Elastic Fibers: Allow stretching and recoil, contributing to flexibility.
- The water content of the skin contributes to skin turgor, maintaining elasticity.
Skin Turgor:
- Defined by the skin's ability to change shape when pinched.
- Dehydrated skin remains peaked when pinched; hydrated skin flattens.
- Loss of turgor can signify dehydration.
Aging Factors:
- Aging, hormonal changes, and UV radiation reduce elastin levels, resulting in wrinkles and sagging.
- Stretching during pregnancy or weight gain can exceed skin's elastic limits, leading to stretch marks.

Tretinoin:
- A vitamin A derivative that can be applied topically.
- Originally used to treat acne; also increases blood flow to the dermis and stimulates repair.
- Reduces wrinkle formation and diminishes existing wrinkles.
- Individual results may vary.

Definition: Arrangement of collagen and elastic fibers in the skin that resist forces of movement.
Clinical Significance:
- Cuts made parallel to tension lines heal better and with less scarring.
- Cuts made perpendicular may open as elastic fibers recoil, resulting in greater scarring.
- Surgeons prefer incisions along these lines (see Figure 5.5).

Arteries:
- Supply skin lying deeper in the subcutaneous layer.
- Form two networks (plexuses) within the dermis.
- Cutaneous Plexus:
- Located along the border of the subcutaneous layer with the reticular layer.
- Supplies blood to hair follicles, sweat glands, and skin tissues.
Subpapillary Plexus:
- Provides arterial blood to capillary loops at the epidermis-dermis boundary.
- Blood from these capillaries drains into veins of the subpapillary plexus, leading to larger veins.
- Trauma can result in bruising due to dermal blood vessel rupture.

The skin contains many sensory nerve endings and receptors.
Functions of dermal nerve fibers include:
- Controlling blood flow
- Adjusting glandular secretion rates
- Monitoring sensory receptors
Types of Receptors:
- Tactile Discs: Fine touch and pressure receptors found in the epidermis.
- Pacinian Corpuscles: Sensitive to deep pressure and vibration, located in the reticular layer.
- Meissner Corpuscles: Sensitive to light touch, found in dermal papillae (see Figure 5.1).
The extensive presence of these receptors emphasizes the skin's role as a sensory organ.

The chapter will revisit the functionality of these receptors in greater detail in future sections (refer to Chapter 15).

Review understanding of the structure and components of the dermis as it relates to its functions.