WHY IS BLOOD RED?
The red colour of blood reflects the colour of
the hemoglobin inside the red blood cells.
This is because the hemoglobin contains iron.
The ‘heme’ of the hemoglobin molecule in
vertebrates (creatures with a backbone) is a
porphyrin ring which surrounds ferrous iron
atoms. It is the spatial relationship between
heme, iron and globin which makes it possible
to bind oxygen molecules reversibly—one to each
iron—and which makes the system so efficient.
lost after forma i t on, leaving them with
their characteristic biconcave shape.
Two reasons have been suggested for
this. First, the relative size of RBCs ( 6–8
µm diameter and just 2 µm thick) 3 and
capillaries (tiny blood vessels) is such
that red blood cells often have to deform
in order to squeeze through. A nucleus
(about 6 µm on average4) could prevent
passage of the cell and make it get stuck,
blocking the circulation.
Second, the shape and deformability
of the red blood cell is optimized for the
carrying and delivery of oxygen, and it
maximizes the amount of hemoglobin
that can be packed into the cell.
Nevertheless birds, which have a very
high oxygen requirement, do fine with
nucleated RBCs, so there are other
design features in birds that compensate
for this. 5
ANDREW HODGE, M.B., B.S., FRACS
Dr Hodge is retired from his former post as
Head of the Cardiothoracic Surgical Service at
the Fremantle Hospital in Western Australia.
A long-time supporter of Creation Ministries
International, he has written for both Creation
magazine and Journal of Creation.
There are about 4–6 million red
blood cells (RBCs) in every cubic
millimetre of blood; 20–30
trillion of them in each
During its 4-month lifetime, each
red cell travels some 500 km (300
miles) around the body, passing
through the heart about 14,000
times per day.
Every day about 1%
of these are changed.
New RBCs take about 7
days to form in the bone
marrow, and are produced
at the staggering rate of about 2
to 3 million every second.
Most of our blood vessels are
the microscopic capillaries. If the
blood vessels in one person were
laid end to end, they would be
about 150,000 km (100,000 miles)
in length—enough to circle the
Each RBC lasts about 120 days
before its components are
recycled to form new RBCs.
earth at the equator about four
*All figures are for a healthy adult
Joggers © iStockPhoto.com/kupicoo EKG MoodyGroove via wikipedia.org
Creation 33( 3) 2011