Hello, welcome to the "Hypertension Medicine Course." I am Jessica.
In the previous lecture, we discussed that blood pressure is
essentially a continuous pulse wave—an energy field that sustains life.
From an energy perspective, humans must solve three problems through
blood pressure:
First, whether it’s upright walking, gathering, hunting, or even
thinking, all these activities consume a lot of energy. How do we meet
these energy demands? Second, the initiation and switching of various
activities must be rapid and decisive. How can energy be quickly
distributed and delivered to where it’s needed most? Third, different
activities involve different organs, and each organ requires varying
amounts of energy. How can we achieve precise distribution?
All of these rely on blood pressure. So, in this lecture, let’s explore
how humans solve these problems through blood pressure mechanisms, and
understand the costs of these solutions.
Main Theme: Long-Term Elevation
Let’s first look at the question: How does blood pressure meet the
energy needs of complex, high-consumption activities like upright
walking, gathering, hunting, and thinking?
Take upright walking as an example. Upright walking was the key step in
our evolution into modern humans. But have you ever wondered, from a
physical standpoint, what is most needed for standing up and walking
upright?
Breathing? Heartbeat? Body temperature? Balance? None of these. The
most crucial requirement for upright walking is a blood pressure that
can remain elevated over the long term.
When transitioning from crawling to standing upright, blood pressure
should theoretically drop to counteract gravity. A drop in blood
pressure means energy and nutrients are not delivered in time
throughout the body—the brain cannot think, limbs cannot move, and
fainting may occur.
Even today, humans still experience orthostatic hypotension—standing up
suddenly from a squat can cause dizziness. This is because blood
pressure temporarily drops to counter gravity, leading to insufficient
cerebral blood flow.
Moreover, humans not only transitioned from crawling to standing but
also needed to run, hunt, and think—complex actions requiring higher
and more stable blood pressure than crawling. How did humans achieve
this?
The story likely goes like this:
About 1.6 million years ago, our ancestors could not stand upright for
long periods. One day, after eating, someone licked an exposed mineral
rock out of curiosity. The rock tasted odd—neither filling nor
thirst-quenching—but soon, many people came from afar just to lick it.
They discovered this mineral had a mysterious power: it allowed them to
stand longer, feel less dizzy, and think more clearly. Over tens of
thousands of years, the love for this mineral became ingrained in our
genes.
Yes, this mineral is sodium chloride—what we commonly call salt.
In addition to increasing sodium intake, humans evolved mechanisms to
retain more sodium by reducing renal excretion, thus maintaining higher
sodium levels in the body for stable blood pressure. This is known as
the "renal-fluid regulation mechanism," which essentially increases
blood sodium concentration.
Why does higher sodium concentration raise blood pressure?
You may know that if you put a salty radish in a bowl of fresh water,
the water will seep into the radish. The same principle applies: when
blood sodium concentration increases, water enters the blood vessels.
As mentioned in the first lecture, blood volume is a variable affecting
blood pressure—greater blood volume naturally raises blood pressure.
Of course, if blood pressure only increased endlessly, the body would
lose its homeostasis and be eliminated. So, when blood pressure gets
too high, the body secretes hormones to prompt the kidneys to excrete
excess sodium, thereby lowering blood pressure and maintaining overall
balance.
In summary, our body maintains a balance of water and sodium. When
the kidneys retain some sodium, water is also retained proportionally,
increasing blood volume and raising blood pressure. Long-term, stable
elevation of blood pressure ensures adequate cerebral blood flow,
enabling upright walking and ultimately the flourishing of human
civilization.
This is the long-term mechanism of blood pressure regulation.
How Is Rapid Distribution Achieved?
Having solved the overall energy demand, the next issue is
distribution.
During various activities, initiation and switching must be rapid. How
is energy quickly distributed to where it’s needed?
To maximize speed, blood pressure regulation signals are transmitted
via nerves. Among all bodily signal transmissions, nerves—using
bioelectricity—are undoubtedly the fastest.
Specifically, blood pressure regulation signals travel along the
sympathetic nervous system, originating from the brain and spinal cord,
reaching organs throughout the body within one second.
Because the sympathetic nerve endings connect to blood vessels in vital
organs such as the heart, lungs, digestive system, and urinary system.
When the sympathetic nerves are excited, their endings secrete
substances like adrenaline, which interact with receptors on blood
vessel walls to exert powerful vasoconstrictive effects.
How Is Precise Regulation Achieved?
After discussing rapid regulation, let’s address the third
question—precise distribution.
Each high-energy activity involves different organs, each requiring
different amounts of energy. However, a single nerve impulse transmits
one signal—either vasoconstriction or vasodilation. How does blood
pressure precisely allocate energy, ensuring more for where it’s needed
and less elsewhere?
Since the starting point of signal transmission cannot be relied
upon, the solution lies at the endpoint—the different types and
quantities of adrenaline receptors on blood vessel walls.
Adrenaline released by nerve impulses only exerts effects when binding
to vascular receptors. Thus, although the nerve impulse is the same,
the types and quantities of receptors vary by location, resulting in
different degrees of vasoconstriction or relaxation. Some receptors
cause stronger constriction, others more relaxation. This enables
precise blood pressure regulation.
These receptors are ancient, existing since invertebrate times. With
the evolution of animal nervous systems, receptor types have become
increasingly diverse. For example, α1 receptors strongly constrict
blood vessels, but α1 has three subtypes with subtle functional
differences, while β2 receptors do the opposite—they dilate blood
vessels.
Why do blood vessels dilate and blood pressure decrease? Is it to
prevent hypertension?
No. Throughout evolutionary history, humans have strived to raise blood
pressure. Lowering local blood pressure and reducing blood flow is
merely a way to better coordinate overall needs—sacrificing less
important areas to ensure vital organs like the brain, heart, and
kidneys receive adequate blood supply.
For example:
Our brain accounts for only 2% of body mass but receives 15% of blood
flow and consumes 25% of total energy. Studies show that even simple
actions like clenching a fist increase blood flow to the brain’s motor
area; reading increases blood flow to the language area; and during
thinking, blood pressure adjusts within one second to supply
corresponding brain regions.
At such times, average distribution is not feasible—blood flow cannot
be allocated based on organ size, but must prioritize vital organs like
the brain. The differentiation of these receptors ensures precise blood
pressure regulation and unequal blood flow distribution.
It can be said that the refined evolution of these receptors enabled
the development of advanced nervous systems and powerful, thinking
brains, ultimately placing humans at the top of the biological chain.
In a sense, blood pressure made humanity possible.
Why Are There So Many Hypertension Patients?
In summary, humans have two blood pressure regulation mechanisms: one
is long-term, stable elevation to meet the energy needs of upright
walking, running, hunting, and thinking; the other is rapid and precise
short-term regulation to distribute energy efficiently for complex
activities.
However, fortune and misfortune are intertwined. The existence of these
two mechanisms has also sown the seeds for today’s hypertension—
Throughout evolution, human blood pressure has mainly trended upward;
lowering blood pressure is merely a supporting mechanism for system
stability. Meanwhile, the organs prioritized for blood supply—such as
the brain, heart, and kidneys—are also the most susceptible to damage
from hypertension.
We are born with these blood pressure regulation mechanisms, making us
naturally prone to hypertension.
When we are young, our blood pressure regulation is sensitive and
quickly restored. But throughout life, external factors like high-salt
diets, obesity, stress, and tension continually stimulate this system,
making it sluggish. Eventually, blood pressure regulation enters a
positive feedback loop, rising uncontrollably with age, making
hypertension inevitable.
Preview of Next Lecture
In the next lecture, we’ll explore: since the mechanisms for elevated
blood pressure are encoded in human genes, is hypertension truly a
disease?
I am Jessica. See you in the next lecture.
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