Page 99 - (DK) I Can’t Believe It! 2

IT CAN’T BE TRUE! 97

FAST FACTS

Blood
cell

Capillary
Some capillaries are so narrow
that only one blood cell at a time
can pass through them. The widest
blood vessel is an artery called
the aorta. At its widest, the aorta
is about 1¼ in (3 cm) across—
about 6,000 times wider than
the narrowest capillary.

65% of blood volume arteries at any one
Veins There is more
blood in the body’s
veins than in the
time. Veins are wider
inside than arteries
(because they have

blood moves more
Arteries 35% of blood volume thinner walls), and
slowly through them.
An
adult human’s
network of
blood vessels
would circle the
world four
times. London to Cologne
309 miles (498 km)

Capillaries are thin—
about 20 of the narrowest A red blood cell is thought to
can fit across the width travel 2.5 miles (4 km) around your
of a hair. These are just body every day. Over its lifetime of
wide enough for one about 120 days, a cell will cover
red blood cell to travel 300 miles (480 km)—that’s just
through at a time. Their under the distance from London
thin walls let substances
pass between the blood to Cologne, Germany.
and the body tissues.

US_096_097_309600_ICBT_Blood_vessels.indd 97 19/12/17 12:56 pm