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| Potassium Control | |
All
multicellular organisms (MCOs), like us, have an intracellular and an extracellular
space. The chemical content of the intracellular fluid (ICF) is totally
different than the chemical content of the extracellular fluid (ECF). In
particular, the ICF has a high concentration of potassium (K+) ions
and a low concentration of sodium (Na+) ions whereas the ECF has the
reverse, a high concentration of Na+ ions and a low concentration of
K+ ions.
As
noted in previous articles, this difference in the Na+ and K+ ion concentrations between the ICF and ECF must be maintained for proper tissue
and organ function, that is, for survival itself.
One
reason for this is that all nerve and muscle function (including the heart) is
dependent on it. All physicians (especially cardiologists) know that maintaining
tight control of the K+ ion level in the serum (fluid component of
blood which is part of the ECF) is critical for human life.
How
this is accomplished in the body has been explained by physiologists but how
this came to be is never really properly explained by evolutionary biologists,
except to say that “It evolved”.
Here’s
why this is so important!
Bioelectricity
of the Cell
As
noted in previous articles, maintaining the proper volume and chemical content
of the ICF and ECF are about a million sodium-potassium pumps in the cell
membrane. They use about one-quarter of the body’s energy requirements at rest
to pump Na+ ions out of the cell and bring K+ ions back
into the cell. Due to this activity, 98% of the body’s K+ ions are
located in the ICF with a concentration that is about 30x more than it is for K+ ions in the ECF. This makes K+ ions the most important positive ions
(cations) in the ICF (Na+ ions are the most important cations in the
ECF—see the last article).
Despite
the work of the sodium-potassium pumps in the cell membrane, diffusion does allow
some K+ ions to leak out of the cell and Na+ ions to leak
back in. The amount of K+ ions lost from the cell in this manner is
much greater than the amount of Na+ ions gained. This net loss of
cations (K+ ions) from the cell makes the inside of the cell
membrane carry a negative electrical charge while the outside carries a
positive charge. This difference in the electrical charge across the cell
membrane is called the “resting membrane potential” (RMP).
The
laws of nature demand that for excitable cells like nerve and muscle (including
the heart) cells to work properly, the RMP must stay within a narrow range. The
number of K+ ions that leak out of the cell, and so determine the
RMP, is directly related to the difference in the K+ ion
concentration between inside (ICF) and outside (ECF) the cell. This means that
to maintain tight control of the RMP, the K+ ion concentration in
the ECF must also be kept under tight control.
But
maintaining tight control of the ECF’s K+ ion concentration is a
dynamic process because the body is always bringing in new supplies of
potassium through the gastrointestinal system while 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 gain and/or lose
potassium. Here are four 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 potassium in solution—onto the
surface of the skin to be evaporated.
2.
The gastrointestinal system efficiently absorbs
potassium but also releases some of it.
3.
When
cells in the body die, they release their high amount of potassium into the
blood.
4.
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 potassium,
from the blood. This fluid moves through millions of microtubules becoming more
concentrated with urea as it becomes urine. If none, or all, of this potassium
were reabsorbed the body would die in 24 hours.
The
Hard Problem
The
body must maintain tight control of the K+ ion concentration in the
ECF. The ECF has about 2% of the body’s total potassium and its concentration
is about 3.5-5.0 units/liter (u/L). Since the total volume of ECF is about 14 L,
this means that the total K+ ions in the ECF is about 60 u.
The
average daily intake of potassium is about 90 u, most of which is readily absorbed
by the gastrointestinal system and put into the blood. This represents 150% of
the total potassium in the ECF. If all of this absorbed potassium were to stay
in the ECF, it would more than double the
K+ ion concentration (> 10 u/L) which would cause death (see below). To prevent
this, most of the K+ ions are pumped into the cells by the
sodium-potassium pumps inside the cell membrane.
When
the concentration of K+ ion in the ECF drops below 3.5 u/L it is
said to be hypokalemic.
As
noted above, the K+ ion level in the ECF directly affects the RMP
which affects nerve and muscle (including the heart) function. Levels below
normal tend to make them less excitable.
Levels
below 3.0 u/L often cause muscle weakness, cramps, twitching, fatigue and
weakness which gets worse as the level approaches 2.0 u/L. Levels between 1.0-1.5
u/L often result in paralysis, respiratory failure, and cardiac rhythm issues
which can be fatal. A K+ ion level less than 1.0 u/L is considered to
be incompatible with life.
When
the concentration of K+ ion in the ECF rises above 5.0 u/L it is
said to be hyperkalemic.
As
noted above, the K+ ion level in the ECF directly affects the RMP
which affects nerve and muscle (including the heart) function. Levels above
normal tend to make them more excitable.
Levels
rising above 6.0 u/L usually cause numbness, tingling, muscle weakness and paralysis
in addition to chest and abdominal pain, nausea and cardiac rhythm issues which
can be fatal. A
K+ ion level more than 8.0 u/L is considered to be incompatible with life. In
fact, intravenous potassium chloride (KCl) is used to
stop the heart in medical executions.
Given
potassium gain from the gastrointestinal system and cell death and potassium
loss mostly from sweating and kidney function, how does the body manage to keep
its serum K+ ion level between 3.5 – 5.0 u/L to maintain proper
nerve and muscle (including the heart) function?
This
is an important practical question for which the body must have an adequate
answer.
And
in contrast to the sodium-potassium pumps, which function the same (static), no
matter what is going on in the body, this represents a dynamic problem which requires
a dynamic 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 maintain tight control of the serum K+ ion level?
Take
a few minutes to think it through.
The
(Dynamic) Innovative Solution
The first thing needed to take control is a sensor
that can detect what needs to be controlled.
The current thinking is that one of the main ways the body controls its
potassium content is through specialized cells in the adrenal glands that have
sensors that can detect the ratio between the blood levels of K+ and
Na+ ions.
The second thing needed to take control is something to integrate the
data by comparing it with a standard (set-point), decide what must be done, and
then send out orders. When these specialized adrenal cells detect a rise in the
ratio of the serum concentration of K+ and Na+ ions they
send out more of a hormone called aldosterone. And when they detect a drop in
this ratio they send out less aldosterone. This means that a rise in the serum
concentration of K+ ions, or a drop in Na+ ions, will
cause these specialized adrenal cells to send out more aldosterone and a drop
in the
K+ ions, or a rise in Na+ ions, will cause them
to send out less aldosterone.
The third thing needed to take control is an effector that can do
something about the situation.
Aldosterone attaches to specific aldosterone receptors on the cells
lining certain microtubules in the kidneys and tells them to release K+ ions into the urine presently in production and bring back Na+ ions
into the blood (ECF).
This means that an increase in K+/Na+ ion will
make the adrenals release more aldosterone which will tell the kidneys to
release more potassium from the body and take back more sodium. And
a decrease in K+/Na+ ion ratio will cause the adrenals to
release less aldosterone which will tell the kidneys to release less K+ ions and bring back less Na+ ions.
Aldosterone does for the body the opposite of what sodium-potassium
pumps do for the cell. It tells the body to get rid of excess K+ ions and hold on to Na+ ions so it can control its total ion content
and serum levels of K+ and Na+ ions. In contrast, the
sodium-potassium pumps let the cell get rid of excess Na+ ions and
hold on to K+ ions, to control its chemical content and volume.
Control of sodium and potassium, from the cellular to the total body
level are inextricably linked.
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 potassium control.
Although the body loses some potassium from perspiration and
gastrointestinal system, most of it is lost through the urine formed in the
kidneys. Every day the kidneys filter about out 180 liters of fluid from the
blood. Since the normal serum level of K+ ion is 3.5-5 u/L, this
means that the kidneys filter out about 600-900 units of potassium daily.
Normal kidney function, combined with the effects of aldosterone,
usually results in the kidneys taking back 85-90% of this potassium and
releasing 10-15%, which amounts to 60-90 u/d. This correlates perfectly with
the amount of potassium usually taken in through the diet and removed from
sweating so that the amount of potassium in the body and serum remains about
the same.
It appears that
the system in the body that uses sensors and hormones with specific receptors
to control its potassium really knows what it’s doing.
“Evolutionary “Explanations”
·
Cell Membrane Function: Potassium is crucial for
maintaining cell membrane potential and function.
·
Kidney Regulation: The kidneys evolved mechanisms to
filter and reabsorb potassium, balancing levels in the body.
·
Hormonal Influence: Hormones like aldosterone play a
significant role in regulating potassium excretion.
·
Dietary Adaptation: Dietary changes influenced
potassium intake and the body's ability to manage serum levels.
·
Evolutionary Pressure: Organisms faced evolutionary
pressures to maintain potassium homeostasis for optimal cellular function.
·
Physiological Mechanisms: Various physiological
mechanisms, including ion channels and transporters, developed to fine-tune
potassium levels.
Questions
Onward!
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