Notesale: Turn your study into money

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The heart is a double pump

Magnified view of blood cells in the human body
(Photo courtesy of National Cancer Institute)

What cells need
• To understand the critical importance of the heart requires taking a
step back so we understand the needs of each cell in our
body
...
Cells have basic needs, and at the top of the list
would be these four things:
• 1) access to oxygen
• 2) a source of glucose
• 3) a balanced fluid environment with the right amount of
water/electrolytes
• 4) removal of waste (such as carbon dioxide)
• Consider how this compares to basic human needs: breathing air in
and breathing out, eating food, drinking water, and getting rid of
urine/stool
...


A breath of air

The lungs are composed of a few hundred million tiny
air sacs called alveoli, each of which are surrounded
by a network of blood vessels (capillary bed) which
carry deoxygenated blood (blue, and carry out
oxygenated blood shown in red
...
21% of the
molecules in this breath are oxygen molecules, and as they
race down into the lungs, they end up in the alveoli which
are tiny air-filled sacs
...
The lungs allow the
oxygen molecules to continue their journey from the gas
phase into a new liquid phase
...

The oxygen diffuses (think of the drop of ink in a pool of
water) into the fluid interstitial space of the lung, and is
then absorbed into the blood stream, and then enters into
the red blood cells themselves
...


The white balls start out on the top and then move all
over the matrix over time through random
movements
...

(Adapted from Wikipedia from Runningamok19)

Why you need your heart
• Now let’s pause and ponder the following:
• What would happen if there was no heart? Well, diffusion of oxygen works
wonders when the distances are very small, but what about large
distances like the distance from your lungs to your feet? Could a single
molecule of oxygen simply diffuse all the way there? In theory, it could—
but it would take a really long time! By the time the oxygen arrived in your
toes by simple diffusion, they would have died and fallen off
...
This is
where hemoglobin, a protein that uses iron to help bind to O2 molecules,
comes to the rescue
...
That means that
each red blood cell can bind ~1 billion oxygen molecules! As a result, the
vast majority (>97%) of the O2 molecules are actually bound to
oxyhemoglobin; with only a minority of O2 molecules floating freely in the
blood
...
(Adapted from Wikipedia image
from Zoofari)

• While air is going in and out of the lungs, the heart is busy
working as well
...

Then, the blood remains in the right atrium, which can be
thought of as a waiting room for the right ventricle
...
Next, the oxygen diffuses from an area
of high concentration (alveoli) to an area of low concentration
(blood), before the blood returns (through pulmonary veins) to
the left of the heart
...
The
left ventricle is a room with even stronger, thicker, and more
muscular walls than the right ventricle
...
For the return trip, blood travels
through the veins of the body to get back to the right side of
the heart and repeat the process
...


Why are there two ventricles?

The heart functions as a double ventricle
...
Blood gets oxygenated in the lungs, moves into
the left atrium, and into the left ventricle where it gets
pumped into the body again

This diagram shows the heart as having a single
atrium and single ventricle
...


• It’s actually a great question, since at first glance it seems
like it would be more efficient to just allow the blood to go
out to the body instead of taking a return trip to the
heart
...
Pressure is
needed to move blood through the resistance of a large
network of blood vessels like arteries, capillaries, and
veins
...
It goes into the
left ventricle where it gets a second squeeze causing the
pressure to rise back up to about 120mmHg (almost 5
times the pulmonary pressure!)
...


Getting the pressure right
• Now, let’s say that the right ventricle raised the pressure up to 140mmHg, then
you may be able to have the blood pressure drop 20mmHg and still be at
120mmHg
...
If exposed to

those high pressures, fluid would get pushed right out of the capillaries and into
the lungs (some capillaries would actually break!), and 2
...
This makes sense when you

remember that none of the capillaries in the body are exposed to extremely high
pressures (120-140mmHg), because by the time blood gets down to the capillaries
it has already passed through arteries (and arterioles), and the pressure has
dramatically fallen

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