integumentary

The integumentary system, commonly referred to as the skin and its associated structures, forms the outer protective covering of the body. It includes the skin itself, its appendages such as hair and nails, and various glands and sensory organs. The system acts as a barrier against mechanical injury, pathogens, and ultraviolet radiation, while contributing to temperature regulation and metabolic processes.

Anatomically, the skin has three main layers: epidermis, dermis, and hypodermis. The epidermis, mainly keratinocytes, includes melanocytes, Langerhans cells, and Merkel cells. The dermis contains connective tissue, blood vessels, nerves, hair follicles, and glands, providing strength and sensation. The hypodermis, rich in fat, anchors the skin to underlying structures and aids insulation. Cutaneous sense organs detect touch, pressure, temperature, and pain.

Accessory structures include hair and nails. Glands have key roles: sebaceous glands secrete sebum to lubricate skin and hair; sweat glands (eccrine and apocrine) regulate temperature and excretion. The skin synthesizes vitamin D in response to sunlight, and epidermal immune cells contribute to defense against pathogens.

Wound healing proceeds through inflammatory, proliferative, and remodeling phases and is influenced by age, nutrition, and disease. Common conditions include dermatitis, acne, psoriasis, burns, and infections, while UV exposure raises skin cancer risk. Protection from UV radiation, hydration, and hygiene are important, with medical evaluation for abnormal lesions.