Dermis

Dermis; corium

Also known as: corium, true skin, papillary dermis, reticular dermis

The dermis is the connective-tissue layer of the skin beneath the epidermis, providing tensile strength and elasticity and housing blood vessels, lymphatics, nerves, sensory receptors and skin appendages.

Show on body map Skin — Layers and Appendages

Overview

Thickness≈1–4 mm (thickest on the back)

Main collagenType I (≈80–85%)

Papillary : reticular thickness≈1 : 4

The dermis (≈1–4 mm thick, thickest on the back) consists of two layers without a sharp boundary. The thin superficial papillary layer is loose (areolar) connective tissue of fine type I and III collagen and elastic fibres. It projects upward as dermal papillae containing capillary loops, Meissner corpuscles and free nerve endings, and interlocks with the epidermal rete ridges. The thick deep reticular layer (≈80% of dermal thickness) is dense irregular connective tissue of coarse type I collagen bundles and branching elastic fibres, embedded in a proteoglycan-rich ground substance (hyaluronan, dermatan sulphate) that binds water and gives turgor.

Cells include fibroblasts (which make the matrix), macrophages, mast cells around vessels, dermal dendritic cells and lymphocytes. The reticular layer contains the deep vascular plexus, the deeper parts of hair follicles and glands, Ruffini endings and arrector pili origins. The predominant orientation of its collagen bundles produces Langer (cleavage) lines, which surgeons follow to obtain fine scars.

On the palms and soles the papillary ridges form the friction ridges (fingerprints). Overstretching tears the reticular collagen, producing striae.

Location: Between the epidermis (above) and the hypodermis (below).

Parts & subdivisions

Papillary layer
Superficial ≈20%: loose connective tissue, fine collagen (types I and III) and elastic fibres, capillary loops of the subpapillary plexus, lymphatic capillaries, Meissner corpuscles, free nerve endings.
Dermal papillae
Finger-like projections into the epidermis; contain either a capillary loop (vascular papillae) or a Meissner corpuscle (neural papillae).
Reticular layer
Deep ≈80%: dense irregular connective tissue with thick type I collagen bundles and elastic fibres; houses the deep vascular plexus, hair follicles, sebaceous and sweat glands, Ruffini endings.
Langer (cleavage) lines
Lines of skin tension reflecting dominant collagen orientation; incisions parallel to them gape less and scar less.

Anatomy

Innervation: Cutaneous sensory nerves (Aβ, Aδ, C fibres) form a dermal nerve plexus; sympathetic fibres supply vessels, arrector pili and sweat glands.
Arterial supply: Deep (cutaneous) plexus at the dermis–hypodermis junction and superficial (subpapillary) plexus at the papillary–reticular junction, linked by candelabra-like ascending arterioles; capillary loops rise into each papilla.
Lymphatic drainage: Lymphatic capillaries begin in the papillary dermis and drain via a deeper dermal plexus to collecting vessels in the hypodermis and then to regional nodes.
Histology: Collagen forms ≈70–80% of dermal dry weight (type I ≈80–85%, type III ≈10–15%). Elastic fibres: fine oxytalan fibres perpendicular to the DEJ in the papillary layer, thicker elastic fibres parallel to the surface in the reticular layer.
Development: Mesoderm: dermomyotome (back), somatic lateral plate mesoderm (limbs and body wall), neural crest (face, anterior neck).

Function

Tensile strength (collagen) and elastic recoil (elastin)
Nourishes the avascular epidermis by diffusion from capillary loops
Thermoregulation via its vascular plexuses and arteriovenous anastomoses
Contains sensory receptors and autonomic nerve fibres
Supports and anchors skin appendages
Immune defence: mast cells, macrophages, dendritic cells, lymphatic drainage to nodes

Clinical significance

Striae distensae (stretch marks)

Linear dermal scars from rupture of reticular collagen and elastic fibres during rapid stretching — pregnancy (striae gravidarum), puberty, obesity. Wide purple striae on the abdomen suggest Cushing syndrome (glucocorticoids inhibit fibroblasts and thin the dermis).

Ehlers–Danlos syndromes

Heritable defects of collagen synthesis or processing: hyperextensible, fragile skin with "cigarette-paper" scars, joint hypermobility and, in the vascular type (collagen III), arterial and bowel rupture.

Langer lines and surgical incisions

Incisions placed along Langer lines (or relaxed skin tension lines) heal with narrow, less conspicuous scars; incisions across them gape and scar more widely.

Test yourself

Langer (cleavage) lines reflect:

The direction of dermatomes
The predominant orientation of collagen bundles in the reticular dermis
The course of cutaneous veins
The arrangement of epidermal ridges

Answer: The predominant orientation of collagen bundles in the reticular dermis

Langer lines follow the dominant orientation of collagen fibre bundles in the reticular dermis. Incisions made parallel to them gape less and heal with finer scars.