Skin Anatomy: Epidermis, Dermis, and Hypodermis Structure and Function

The skin is the body's largest organ, composed of three layers:

1. Epidermis (Outermost)

Stratified squamous keratinized epithelium. Avascular; nourished by diffusion from dermis.

• Keratinocytes (90%): Produce keratin; form barrier; undergo terminal differentiation (stratum basale → corneum)
• Melanocytes: Produce melanin (UV protection); transfer to keratinocytes via melanosomes
• Langerhans cells: Dendritic antigen-presenting cells; immune surveillance
• Merkel cells: Touch sensation (with nerve endings)

Sublayers (deep to superficial): basale, spinosum, granulosum, lucidum (thick skin only), corneum.

2. Dermis (Middle)

Dense irregular connective tissue (collagen, elastin). Vascularized and innervated.

• Papillary layer: Loose CT, dermal papillae (fingerprints), Meissner's corpuscles (light touch)
• Reticular layer: Dense CT, sweat glands, hair follicles, sebaceous glands, Ruffini endings (stretch), Pacinian corpuscles (deep pressure/vibration)

3. Hypodermis (Subcutaneous)

Adipose tissue (fat) and areolar CT. Insulates, cushions, stores energy, anchors skin to fascia.

Functional Integration

Epidermis provides barrier; dermis supplies nutrients, immune cells, sensory input, and appendages; hypodermis insulates and contours.