Dermis

The dermis is the layer of skin situated between the epidermis and the subcutaneous tissue (hypodermis). It is a connective tissue layer that provides structural support, elasticity, and strength to the skin.

Structure and Composition

The dermis is composed primarily of collagen fibers (predominantly type I and type III), elastic fibers, and ground substance (glycosaminoglycans and proteoglycans) embedded within an extracellular matrix. It is divided into two distinct layers:

• Papillary dermis — The thin, superficial layer directly beneath the epidermis. It consists of loose connective tissue with thin collagen fibers and contains the dermal papillae, which interdigitate with the epidermal rete ridges to increase the surface area of the dermoepidermal junction. This layer is rich in capillary loops and sensory nerve endings (e.g., Meissner corpuscles).

• Reticular dermis — The thicker, deeper layer that constitutes the bulk of the dermis. It is composed of dense irregular connective tissue with thick bundles of collagen fibers oriented parallel to the skin surface (Langer lines). This layer provides the skin's primary tensile strength.

Key Components

The dermis contains several important structures:

• Vascular network — Organized into a superficial (subpapillary) plexus and a deep (subdermal) plexus, responsible for thermoregulation and nutrient delivery to the avascular epidermis.

• Nerve supply — Free nerve endings for pain and temperature, as well as encapsulated receptors (Meissner and Pacinian corpuscles) for touch and pressure.

• Adnexal structures — Hair follicles, sebaceous glands, eccrine and apocrine sweat glands, and arrector pili muscles are all housed within or traverse the dermis.

• Cellular components — Fibroblasts (the predominant cell type, responsible for collagen and extracellular matrix synthesis), mast cells, macrophages, dendritic cells, and lymphocytes.

Function

The dermis serves as the structural scaffold of the skin, providing mechanical protection, thermoregulation, sensory perception, and immune surveillance. It also plays a critical role in wound healing through fibroblast proliferation and collagen deposition.

The thickness of the dermis varies by body site, ranging from approximately 0.3 mm on the eyelids to 3.0 mm or more on the back and palms/soles.