Skin Layers Explained: Epidermis, Dermis, and Hypodermis Structure and Function

The skin (integumentary system) is the body's largest organ, covering approximately 1.5–2 m² and accounting for about 15% of body weight. It consists of three primary layers:

1. Epidermis (Avascular, Stratified Squamous Epithelium)

• Stratum Basale: Contains stem cells, melanocytes (produce melanin), and Merkel cells (touch sensation).
• Stratum Spinosum: Keratinocytes with Langerhans cells for immune surveillance.
• Stratum Granulosum: Keratohyalin granules and lamellar bodies secrete lipids.
• Stratum Lucidum: Present only in thick skin (palms and soles).
• Stratum Corneum: 15–30 layers of anucleate corneocytes embedded in a lipid matrix—provides barrier function, preventing transepidermal water loss and excluding pathogens.

2. Dermis (Connective Tissue)

• Papillary Layer: Loose connective tissue with dermal papillae (fingerprints), Meissner's corpuscles (light touch), and capillary loops.
• Reticular Layer: Dense irregular connective tissue (collagen I/III, elastin) housing hair follicles, sebaceous and sweat glands, Ruffini and Pacinian corpuscles (stretch and vibration), and a vascular plexus.

3. Hypodermis (Subcutaneous Tissue)

• Adipose tissue for energy storage, insulation, and body contour.
• Fascial planes, neurovascular bundles, and ligamentous attachments.

Skin Appendages

Hair, nails, sebaceous glands (sebum), and eccrine/apocrine sweat glands—all are epidermal derivatives residing in the dermis and hypodermis.