DK - WOW! The Visual Encyclopedia of Everything

Skin is the body’s protective overcoat, forming a

barrier between vulnerable body tissues and the harsh,

changing conditions of the outside world. It prevents

water loss, blocks invasion by germs, repairs itself

when damaged, helps us keep warm, and enables

us to sense our surroundings. The uppermost layer

of the skin is made from dead cells filled with a

tough, waterproof substance called keratin. Hair

and nails, both derived from skin, are also made

from dead, keratin-filled cells.

Skin, hair, and nails

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(^1) SKIN CROSS-SECTION
A section through the skin reveals that
it has two parts. The epidermis is a
germ-proof, waterproof barrier that
protects against harmful rays in sunlight.
The thicker dermis contains blood vessels,
sensory receptors, and sweat glands.
(^2) SWEAT
This salty liquid is produced by sweat
glands in the dermis. In hot conditions,
sweat is released onto the skin’s surface.
It then evaporates, cooling the body
and helping to maintain a constant
body temperature of 37°C (98°F).
(^3) SKIN COLOUR
Special cells in the epidermis
produce the brown pigment
melanin, which filters out
harmful ultraviolet rays
from sunlight before
they can damage
skin cells.
Surface of
the epidermis on
the back of a
person’s hand
Melanin, along
with blood flowing
through the dermis,
gives the skin

Colour spectrum

The dermis contains

living cells and fibres

that allow skin to

stretch and recoil

Cells in the base of the

epidermis divide constantly

to replace those lost

from the surface

The epidermis consists of

cells that migrate upwards,

dying, flattening, and filling

with keratin as they do so

Flat, scaly cells in

the upper epidermis

are constantly worn

away as skin flakes

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2

3

Skin surface is not

smooth but covered

with ridges into which

sweat spreads

Sweat is a watery

solution, filtered from

blood and containing

salts and wastes, that

oozes from small

openings called pores

074_075_Skin.indd 74 03/01/19 12:09 PM