CorpusHuman Anatomy

Skin — Layers and Appendages

Three-dimensional block of thin hairy skin with a magnified view of the epidermis

A block of thin (hairy) skin cut to show its three layers: the avascular epidermis on top, the dermis (loose papillary layer with dermal papillae and capillary loops above, dense reticular layer with coarse collagen below) and the fat-filled hypodermis. The magnified panel shows the four strata of thin-skin epidermis with its resident melanocyte, Langerhans cell and Merkel cell; thick skin of the palms and soles would add a stratum lucidum.

A hair follicle with its sebaceous gland and arrector pili (the pilosebaceous unit) slants through the dermis; an eccrine sweat gland coils at the dermis–hypodermis junction and sends its duct to a surface pore (watch the sweat droplets), while an apocrine gland — present only in axillary and anogenital skin — empties into the follicle. Meissner corpuscles sit in dermal papillae, Pacinian corpuscles deep in the hypodermis and free nerve endings penetrate the epidermis. Blood flows from hypodermal arteries through the deep and subpapillary plexuses into capillary loops that nourish the epidermis by diffusion. Vertical proportions are exaggerated: the epidermis is really only ≈0.1 mm thick compared with a 1–4 mm dermis.

Step-by-step

  1. Skin surface and hair

    The surface is the stratum corneum, criss-crossed by fine furrows and pierced by hair shafts and sweat pores. Hair covers almost all thin skin; it is absent from the palms and soles.

  2. Epidermis

    A keratinised stratified squamous epithelium with no blood vessels. In thin skin it has four strata — basale, spinosum, granulosum and corneum; cells take about four weeks to travel from the basal layer to the surface and be shed.

  3. Resident epidermal cells

    Melanocytes in the basal layer pass melanin to keratinocytes, where it forms caps over the nuclei. Langerhans cells in the spinous layer capture antigens and carry them to lymph nodes. Merkel cells with their nerve discs sense sustained pressure.

  4. Papillary dermis

    Dermal papillae interlock with the epidermal rete ridges. Each papilla holds a capillary loop or a Meissner corpuscle (light touch, flutter); free nerve endings for pain, temperature and itch run up into the epidermis.

  5. Reticular dermis and pilosebaceous unit

    Dense irregular connective tissue gives the skin its strength. The hair follicle grows from its bulb around the dermal papilla; the sebaceous gland empties sebum into the follicle, and the arrector pili muscle (sympathetic) erects the hair and squeezes the gland.

  6. Sweat glands

    The eccrine gland coils at the dermis–hypodermis junction. Its secretory coil makes a plasma-like fluid, and the duct reabsorbs NaCl so that hypotonic sweat reaches the pore; sympathetic cholinergic nerves drive it. The apocrine gland (axilla and groin only) empties into the hair follicle.

  7. Blood supply

    Arteries in the hypodermis feed a deep plexus at the dermis–hypodermis junction and a superficial subpapillary plexus. Capillary loops rise from the subpapillary plexus into the papillae. Changing flow through these plexuses is the main way the body regulates heat loss.

  8. Hypodermis

    Lobules of adipocytes separated by fibrous septa insulate, store energy and cushion. Large vessels and cutaneous nerves run here, together with the onion-like Pacinian corpuscles that detect high-frequency vibration.

Labelled parts