 |
|
| Sodium
Control
|
|
The human body consists of trillions of cells made up
of atoms and molecules affected by the forces of nature and the laws that
govern them. These laws demand that each cell have enough energy, water and
various chemicals to do what it needs to do to live and work properly.
The cells get what they need from the blood that travels
in the cardiovascular system. However, getting
enough blood flow to the tissues depends on having enough blood volume. And
having enough blood volume depends on the body having enough total water with
the right distribution.
The last few articles explained how the body
distributes and controls its total water content.
Sodium-potassium pumps in the cell membrane maintain
the 2/3:1/3 ratio between the water inside the cells (intracellular fluid
(ICF)) and outside the cells (extracellular fluid (ECF)).
Albumin in the blood maintains the 80:20 ratio between
the water between the cells (interstitial fluid (ISF)) and inside the
circulation (intravascular fluid (IVF)) which make up the ECF.
The body uses Anti-Diuretic Hormone (ADH) to control
its total body water (TBW) by it stimulating the thirst center and continuously
telling the kidneys how much water to excrete.
But That’s Not All
Having enough water in the circulation is dependent on
another chemical—sodium. If the body didn’t have enough sodium, there wouldn’t
be enough water in the circulation and there would be no human life.
Here’s why.
As noted above and previous articles have explained, to
maintain its proper volume and chemical content the cell membrane has sodium-potassium
pumps that constantly push Na+ ions, and with them, water, out of
the cell to prevent a toxic build-up. Without enough of these pumps, doing what
they’re supposed to do, all of the ECF would tend to move into the ICFcell death.
Due to the action of the sodium-potassium pumps over
90% of the body’s sodium is in the ECF and its Na+ ion concentration
is about ten times more than that of the ICF. So, one can see that the Na+ ion is the most important positive ion (cation) in the ECF. And since the IVF (blood
volume) represents about 20% of the ECF, this means that the Na+ ion
is also the most important cation in the blood as well.
But
maintaining control of the body’s sodium content is a dynamic process because
it is always bringing in new supplies through the gastrointestinal system and
losing it through other means.
Let’s
take a closer look!
Following
the Rules of MCO (Human) Life
Life
doesn’t happen within a vacuum nor the vivid imaginations of evolutionary
biologists. The reality is that living within the forces of nature, and the
laws that govern them, obligates the body to constantly lose sodium to its
surroundings. Here are three reasons why.
1.
The
body must maintain its temperature within a narrow range so its cellular enzymes
can work right. The more active the body, the more heat it produces, which must
be released to keep its temperature under control. One way is by
perspiration—the secretion of water containing sodium in solution—onto the
surface of the skin to be evaporated.
2.
To do its job the gastrointestinal system secretes a
lot of fluids containing saline (NaCl) and sodium bicarbonate (NaHCO3). Most of
the sodium within these fluids is brought back into the body, but some of it is
lost through the feces.
3.
Protein metabolism produces ammonia which the liver converts into a
more soluble molecule called urea. The build-up of ammonia and urea in the body
can be toxic. The kidneys continuously filter water, containing sodium, from
the blood. This fluid moves through millions of microtubules becoming more
concentrated with urea as it becomes urine. If none of this sodium could be
reabsorbed the body would die in 30 minutes.
The
Hard Problem
Since,
through these three processes, the body is always losing sodium, it is therefore
always at risk of dying from not having enough sodium in the blood. Taking in
salt may solve some of the problem, but how much is enough and how much is too much?
In
real life, the Na+ ion concentration in the ECF is mostly determined
by the TBW content and not necessarily by how much total sodium is in the body.
When
the body loses too much water (dehydration) this causes the Na+ ion
level to rise too high (hypernatremia) resulting in fatigue, weakness,
confusion, seizures, coma and death. The body could have a low amount of total sodium,
but if at the same time the water content is too low, its ECF is hypernatremic, resulting in the above.
When
the body has too much water, this causes the Na+ ion level to drop
too low (hyponatremia) resulting in fatigue, weakness, confusion, seizures,
coma and death. The body could have a high amount of total sodium, but if at
the same time the water content is too high, its ECF is hyponatremic, resulting
in the above.
Just
as the sodium-potassium pumps push out Na+ ions and thereby prevents
water from entering the cell, so too, when it comes to the ECF, the body has to
take into account not only how much sodium is in the body but also its TBW
content as well.
So,
how much sodium and water can the body ingest and depending on its level of
activity, release through the skin, gastrointestinal tract and kidneys to stay
alive and thrive?
All
of these are important practical questions for which the body must have
adequate answers.
And
in contrast to the sodium-potassium pumps and albumin, which function the same
(static), no matter what is going on in the body, this represents a dynamic
problem requiring a solution.
Here’s
how Steve Laufmann and I explained the situation in our book Your Designed Body.
“The
body must manage the right functional capacities, with exactly the right timing
(dynamics) for all its systems, such that they can support the entire range of
the body’s needs. The body must use thousands of different signals—chemical,
electrical, or both in combination—to coordinate and control all the systems.
Each signal must be triggered at the right time and place, sent over some
distance, then received and interpreted at another specific location to produce
a specific outcome. Controls must work within critical time constraints. The
time required to start and stop various systems, communications transmission,
speeds, capacity ramp up and response times and the proper “locality of effect”
are all critical to life.”
What
type of innovation do you think would be needed to solve this really hard
problem?
What
sorts of information would be needed to manage the ongoing sodium needs of the
body?
Take
a few minutes to think it through.
The
(Dynamic) Innovative Solutions
The first thing needed to take control is a sensor
that can detect what needs to be controlled.
Just like when air is pumped into a tire, as blood
flows through a blood vessel, or into a chamber, the force it applies against
its walls causes them to stretch. Some of this wall movement is due to the
amount of blood within the circulation, which is a reflection of its water
content. However, since the amount of water in the blood is also dependent
on its sodium content, this means that the wall motion that takes place as
blood flows into a blood vessel or chamber is also a reflection of the body's
sodium content as well.
One set of sensors that detect this wall motion are
located near the arterioles within the kidneys, where blood enters to be
filtered. And another set of sensors are located in the walls of the upper
chambers of the heart (atria).
The sensory cells in the kidneys release a hormone,
called renin, in an amount that is inversely related to how much wall motion
they detect. The more the walls stretch, indicating more blood volume, the
less renin is sent out, and the less the walls stretch, indicating less volume,
the more renin is sent out.
The atrial cells send out a hormone, called Atrial
Natriuretic Peptide (ANP, a natriuretic is a chemical that causes the
excretion of sodium (L. natrium = sodium)), in an amount that is directly
related to how much wall motion they detect. The more the walls stretch,
indicating more blood volume, the more ANP is sent out, and the less the walls
stretch, indicating less blood volume, the less ANP is sent out.
Renin is an enzyme that acts on angiotensinogen, a
protein made in the liver, to form another protein called angiotensin I.
Angiotensin I is acted upon by an enzyme in the lungs to produce angiotensin II.
Angiotensin II not only stimulates the thirst center but also the appetite for
salt. Angiotensin II also attaches to
specific angiotensin II receptors on certain cells in the adrenal glands and
tells them to release a hormone called aldosterone. Aldosterone attaches to
specific aldosterone receptors on the cells lining some of the microtubules in
the kidneys and tells them to bring more sodium back into the body.
The final effect of renin is to make the body increase
its sodium content by taking in more salt and taking back more Na+ ions from the urine in production.
In contrast, ANP reduces the desire for salt and
blocks the release of renin and aldosterone. It also attaches to specific ANP
receptors on the microtubules in the kidneys and tells them to release
more sodium into the urine.
The final effect of ANP is to reduce the intake of
sodium and to increase its release from the kidneys. ANP acts as a
counterbalance to renin.
The way the body makes sure it has enough sodium is
not just as simple as taking in salt. Neither is it as simple as just having properly working gastrointestinal
and renal systems.
But that’s not all!
Real
Numbers Have Real Consequences
Physicians
and engineers do their work within the real world where real numbers have real
consequences—even death! Here is how we expressed it in Your Designed Body.
“Physicians
don’t get to make stuff up. They don’t have the luxury to merely observe how
life looks or theorize about its superficial qualities. They need to know how
the body really works, how the parts affect each other, and what it takes in
practical terms to keep it all working over a (hopefully) long lifetime. Though
their mistakes sometimes take longer to discover than those of physicians,
engineers also must live in the real world. Engineers design, build, deploy,
and operate complex systems that do real work in the real world. And it takes
yet more work to keep the systems from failing.”
As
opposed to physicians and engineers, the concept of “functional capacity” seems
to be totally absent from the mindset of evolutionary biologists. That’s
because their theoretical constructs always lack the objective criteria needed
to verify that a given biological structure works well enough for survival—in
other words its functional capacity and the control mechanisms needed to
maintain it are good enough
Yet,
no matter how complex the genetics leading to a sophisticated biological
structure, if it can’t control and maintain the functional capacity to combat and/or
use the laws and forces of nature to its advantage, the organism in which it is
housed is as good as dead.
The
same applies to sodium control.
Since the body is always losing sodium through the gastrointestinal
system, perspiration, and urine formation, one way for it to try to control its
sodium content is to take in sodium (table salt). The gastrointestinal system
readily absorbs all of the sodium it receives independent of the body's actual
needs. But how much sodium is enough and what happens if you don’t take in
enough or you take in too much?
Do you think our earliest ancestors were able to make these
determinations and do what was right to stay alive? The minimum daily
amount of sodium needed is about 500 mg but most people take in about 3,000 to
4,000 mg per day. So, how the does the
body deal with the excess?
It is the kidneys that control the body's sodium content. Every
hour they filter 7.5 liters of fluid out of the bloodstream, which represents
about one sixth of the body's total water content. But, because the plasma
has such a high Na+ ion concentration, in that hour it also filters
out about one-half of the body’s total sodium content as well.
The microtubules in the kidneys automatically take back about 85% of
the sodium they filter. But that still
leaves the remaining 15%. Without the presence of aldosterone to tell them to
bring most of it back into the body, death would take place in just under four
hours.
In fact, the total absence of aldosterone is incompatible with life.
The effects of aldosterone and ANP tell the kidneys to bring back about
99.5% of the sodium they filter so life can continue. The effects of the
kidneys controlling the water and sodium content of the body results in the
normal serum Na+ ion level being about 135-145 units.
“Evolutionary
“Explanations”
Questions
Onward!
|