Life is in the
blood
By Andrew Hodge
“For the life of
the flesh is in the blood”
So says Leviticus 17:11.
Everyone knows that we must have enough blood
flowing around our body or else our bodily functions deteriorate and we die.
Yet for a long time the exact function of
blood was little understood. In what ways has modern science shown Leviticus
17:11 to be true?
Blood is fundamental to the function of every
cell of every component in our bodies.
Cells need food to survive, grow, repair
themselves and to fulfill their specific functions, and, to reproduce. Cellular
food is transported in blood to provide energy for all the cells’ needs.
As humans are multicellular organisms, having
separate specialized organs with highly sophisticated functions, transport and
communication between these structures is essential.
As humans are multicellular organisms, having
separate specialized organs with highly sophisticated functions, transport and
communication between these structures is essential.
Coordination
Do the
cells of the body tell the blood how it should work? No.
Does the blood carry around everything
possible just in case? No.
The cells and the blood work together to
provide optimum conditions for correct functioning of all the cells—with their
different requirements—in all the tissues and organs of the whole body,
including the cells of the blood itself.
Blood provides this coordinated environment
by regulating acidity/alkalinity (pH), providing oxygen (and removing carbon
dioxide and other waste products), and carrying essential vitamins and
minerals.
Also, blood has to be in the right places at
the right times, at the right temperature and pressure, and it carries
regulatory messages between organs via blood ‘messengers’ called hormones.
All this is organized within very specific
limits—straying outside these (through injury, disease, toxins, etc.) rapidly
reduces functionality.
Hormonal
feedback
Words
matter
FLESH (as used in many English translations of Leviticus 17:11):
Hebrew בשר basar, the tissues that make up the body, and (by
extension) also the body, the living creature.
TISSUE: a collection of cells (not necessarily the
same type) grouped for a specific function. E.g. connective tissue, muscle
tissue. Blood itself is, technically speaking, also a tissue.
ORGAN: several types of tissue functionally
grouped together, e.g. liver, lung.
Hormones, those important chemical messengers
in the blood, are involved in self-regulating feedback systems. These systems
stimulate hormone production in times of lack, and suppress it in times of
plenty.
For example, when we eat, the sugars in the
intestine are digested and absorbed into the local bloodstream. This blood then
passes through the pancreas and its higher sugar level stimulates production of
the hormone insulin.
As insulin is distributed in the bloodstream,
it reduces the blood sugar to normal levels again by increasing the amount of
sugar that all cells take in.
In fact the brain relies almost entirely on
sugar (specifically glucose) for its energy supply; hence this feedback system
is absolutely critical for proper brain activity. If the blood glucose ever
drops too much, we lose consciousness.
The body’s systems tend to be wisely
over-engineered, so that one might predict that there is also a system to cope
with low sugar levels, for example when we exercise and use sugar up.
This system uses the hormone glucagon (also
from the pancreas) and it works by releasing glucose into the blood from stores
located mostly in the liver.
There are about fifteen organs classed as
hormone-producing (endocrine) glands, and
their products, carried by the blood, affect either every cell in general or
specifically target certain cells.
Widely known examples are the male and female
hormones testosterone and estrogen, adrenaline (epinephrine in the US), the
thyroid hormone thyroxine, and many more.
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.
Targets
For
example, thyroxine regulates the speed of metabolism in every cell, and having
the correct amount (within narrow limits) allows normal cellular activity.
Too much and we become ‘hyper’, too little
and we are slow and lethargic.
Another example is gastrin. The target organ
for gastrin is that part of the inner lining of the stomach which produces
hydrochloric acid for digestion.
Food in the last part of the stomach
stimulates the production of gastrin, which is carried back by the blood to
stimulate acid production. This is a positive feedback mechanism in which blood
is the essential communicating link.
Anticipation
Blood
also has a major role in body protection in that it is an integral part of the
immune or infection-fighting system, involving antibodies and white blood
cells.
It also possesses a highly complex mechanism
to prevent its own loss from the body (clotting) and to prevent clotting inside
the body (thrombosis).
The capacity to quickly initiate clotting
outside and to limit—even reverse—clotting on the inside is provided by
‘cascades’—cumulative processes in which each step of the process is dependent
on the one before it.
The cascades are of such complexity that new
factors, cofactors and regulators are being constantly added to our body of
knowledge.
It is now known that there are more than a
hundred factors or steps that make up the clotting cascade. Such details add to our appreciation of how finely
balanced, effective and versatile the system is.
But a greater marvel is that such a system,
which is there in anticipation of blood loss, internal injury or disease,
should be there at all.
Unique
red blood cells
Having a molecule such as
hemoglobin which can handle oxygen so quickly and reversibly, when required, is
amazing.
Red blood cells (RBCs or erythrocytes) form
the majority of the cells in the blood—and a quarter of all cells in the human
body.
They are unique among all others—in mammals,
they have no nucleus and none of the usual energy-producing structures in the
cell outside the nucleus. This is a design feature of mammals (creatures which,
like us, suckle their young).
Normally, a cellular nucleus carries the DNA
which instructs the cell on how to perform its functions, including repair and
reproduction, at the appropriate times.
RBCs cannot do this because instead they are
especially designed to carry oxygen, and in humans, having a nucleus would
hinder this essential function. So the nucleus is lost after formation, leaving
them with their characteristic biconcave shape.
Blood
bytes*
There
are about 4–6 million red blood cells (RBCs) in every cubic millimetre of
blood; 20–30 trillion of them in each person.
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.
Each RBC lasts about 120 days before its
components are recycled to form new RBCs.
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.
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 earth
at the equator about four times!
*All figures are for a healthy adult
Two reasons have been suggested for this.
First, the relative size of RBCs (6–8 µm diameter and just 2 µm thick) 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.
The system of the red blood cells giving
oxygen to the cells of the tissues is reversed when the red blood cell reaches
the lungs, where it gives up its carbon dioxide (though this is mostly carried
by plasma) and takes on a new load of oxygen.
At rest, all the blood (5 litres in an adult)
completes a circuit within a minute (spending 1 to 3 seconds in the
capillaries). With exercise, circulation is as quick as every 10 seconds.
Having a molecule such as hemoglobin which
can handle oxygen so quickly and reversibly, when required, is amazing.
Conclusion
So is
the life of the flesh in the blood?
Although not confirmed by science until
modern times, this statement from Leviticus 17:11 has
always been true.
Blood actively maintains life by providing a
vital function for all cells, tissues and organs, and thus the life of the
whole body.
The more we find out about the astounding
functional design and complexity of blood, the more marvellous it becomes to
us, and the more honour and praise is due its Creator.
The
function of the blood clotting system is to prevent the escape of blood from a
damaged vessel.
To do this, the blood has a special and very
complex repair procedure in place.
Once initiated by a cut, the first component
in the process is activated, which in turn activates the next component, and so
on, in a series of cumulative, mutually-dependent steps.
This physiological chain of production, or
cascade, results in the formation of a solid obstruction (a clot) in order to
seal over the damage.
Some of the main components of the clotting
cascade are the proteins fibrinogen, prothrombin, Stuart (anti-hemophilic)
factor and proaccelerin. None of these are used for any other purpose in the
blood.
The system is very finely tuned to result in
a repair process that achieves just the repair needed at just the right place
and time to stop bleeding and begin the process of healing.
Importantly, the process is also
self-limiting to ensure that coagulation (clotting) of the entire blood supply
does not occur.
The Intelligent Design advocate Michael Behe,
in his book Darwin’s
Black Box, has
noted that the clotting cascade is an example of irreducible complexity.
The removal or degradation of just one, any
one, of the components or steps would cause the cascade to fail. Obviously this
would have dire consequences for the organism.
It is exceedingly difficult to see how the
clotting cascade could have evolved, as any postulated simplified or
‘primitive’ version of the process would result in failure.
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