Our sense organs 45

The entire molecule, consisting of 10,000 atoms,
has a molecular weight of about 68,000 (compare:
H 2 O: 18, CO 2 : 44, insulin: 41,000). It is precisely
folded in such a way as to obtain its characteristic
near-spherical shape (diameter: 5.5 nm,
1 nm = 10 -9 m). Each of its four equal sized parts
is also roughly spherical.
only diffuse into body tissues when it is physically
dissolved. But most of the oxygen transported
by the blood is bound to Hb, maximally in the
ratio of four oxygen molecules per molecule of
Hb. It follows that one gram of Hb can absorb
1.36 ml oxygen (Hüfner’s number). The average
man has 15.3 g of Hb per 100 ml blood, and a
woman has 14.5 g Hb, so that each 100 ml of a
man’s blood can carry 20.8 ml O 2 (19.7 ml in the
case of a woman), when all the heme is fully oxygenated.
Hb thus transports 70 times as much
oxygen as that which can be physically dissolved
in the serum. The total amount of Hb in 5.5 litres
of blood is between about 745 and 820 g.
Some noteworthy numbers:
Large lymphocyte
When oxygenated, the colour of the blood changes
from dull purplish (the venous blood depleted of
oxygen) to a bright scarlet (the colour of oxygenrich
arterial blood). Oxygenated Hb is known as
oxy-hemoglobin. The theoretical oxygen capacity
of the 5 – 6 litres of blood in the body is between
1,100 and 1,400 ml, but only 25 % of this
amount is actually utilised. In an equal volume of
water (5 – 6 litres) at 20 °C only 150 – 180 ml
oxygen can be dissolved (and even less at 37 °C).
When carbon monoxide (CO) is inhaled, it
replaces oxygen, because it binds more tightly
with Hb. This explains the high toxity of even
small concentrations of CO in the air.
A fraction of the oxygen is transported by the
blood in the form of dissolved O 2 , as is the case
with other respiratory gases. Although this quantity
of oxygen (0.3 ml per 100 ml blood) is
minute, it is quite important, since oxygen can
The total number of red blood
corpuscles:
25 million million
That is,
– in one cubic millimetre (mm 3 ): 5,000,000
– in one drop of blood: 250,000,000
– in one cubic cm (cm 3 ): 5,000,000,000
Total surface area of all red blood cells: 3,800 m 2
Total number of white blood cells:
35,000 million
Total number of platelets:
1.25 million million
To get some visual grasp of the immense number
of erythrocytes in our body: If all these red blood
cells were stacked one on top of the other, the
stack would reach a height of 40,000 km, the circumference
of the earth at the equator. If all 25
million million red blood corpuscles were laid
down next to one another, we would have a
190,000 km long band which would be nearly
five times the circumference of the earth.
Red blood cell differences before and after
birth: Concerning the transport of oxygen in the
blood, two requirements must be met right
throughout the three different stages of the
human being (embryonic, fetal and adult) considered
here. All parts of the body must be supplied
with the necessary amounts of oxygen; similarly,
the CO 2 resulting from oxidation needs to be
transported away. Each of these various developmental
stages has differing circulatory and
metabolic situations, so the capacity of the blood
to transport these gases needs to be different in
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