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Human Body Study

Integumentary System

The body’s outer wrapping — the skin, plus hair, nails, and assorted glands. The skin is the body’s largest organ by surface area and weight.

The skin and its appendages A cross-section of skin showing its three layers — epidermis, dermis and hypodermis — together with the hair, sebaceous glands and sweat glands that pass through them. A small inset shows a fingertip with its nail. Each label links to the article for that part. Nails Epidermis Hair Sebaceous glands Dermis Sweat glands Hypodermis Cross-section of skin and its appendages — schematic, not to scale.

Main parts

Section titled “Main parts”
  • Epidermis — the thin, tough outer layer; constantly shed and renewed.
  • Dermis — the thicker living layer beneath, holding blood vessels, nerves, and glands.
  • Hypodermis — the fatty layer below, anchoring and insulating the skin.
  • Hair — keratin threads growing from follicles.
  • Nails — keratin plates protecting the fingertips and toes.
  • Sweat glands — produce sweat for cooling and waste removal.
  • Sebaceous glands — produce oily sebum that lubricates skin and hair.
  • Pilosebaceous unit — the integrative unit of hair, sebaceous gland, and arrector muscle on which most of the skin is built.

What it does

Section titled “What it does”
  • Barrier — keeps water in and microbes, chemicals, and UV radiation out.
  • Temperature control — sweating and adjusting blood flow shed or conserve heat.
  • Sensation — packed with receptors for touch, pressure, temperature, and pain.
  • Synthesis — makes vitamin D when exposed to sunlight.

Key idea

Section titled “Key idea”

The skin is not a passive covering but an active organ — a barrier, a sensor, a radiator, and a chemical factory all at once.