The Integumentary System
The three layers of skin and what lives in each, how skin controls temperature, what burn depth actually describes, and why the skin is the first organ that tells you a patient is compensating.
8 min read · Updated September 10, 2026
The Largest Organ
Skin is an organ, and it is the largest one the body has, covering roughly two square meters in an adult and accounting for about 16 percent of body weight.
It does five jobs: it keeps pathogens out, it keeps fluid in, it regulates body temperature, it senses touch, pressure, temperature and pain, and it manufactures vitamin D on exposure to sunlight.
Skin is also the organ you assess first and most often, because it reports on circulation faster than almost anything else you can measure.
Quick check
Why is the skin the organ the EMT assesses first and most often?
Frequently asked questions
What are the three layers of the skin?
The epidermis is the outer layer with no blood vessels of its own. The dermis underneath holds the capillaries, nerve endings, sweat glands, hair follicles and sebaceous glands. Below both sits the subcutaneous layer of fat and connective tissue, which insulates and cushions.
How does the skin control body temperature?
Vessels in the dermis widen to bring warm blood to the surface and shed heat, and narrow to keep blood deep and hold heat in. Sweat glands add evaporative cooling. Those two mechanisms are also why a patient in shock has pale, cool, sweaty skin, because the vessels have clamped down while the sympathetic response drives the sweat.
What does burn depth describe?
How far down through the layers the burn has gone. Superficial involves the epidermis only and is red, dry and painful. Partial thickness reaches the dermis and blisters, and it is the most painful because the nerve endings are exposed and alive. Full thickness destroys the whole dermis, so it can look white, brown or charred and be painless where it is deepest.
Now go use it
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