I'm going to draw
a person for you, and this is going to be my
side profile of this person. Let's say something like this. And this person has--
I'm going to draw it kind of loosely-- let's
say, two arms and one shoulder apparently. I need to draw in
another shoulder. There we go. So this is my person. And I'm going to
draw in their brain. This is their brain. And they have a heart. This is their heart here. And now you know
there are nerves that come down from the brain
and serve the heart, right? So these are nerves
that are basically going to tell the heart to
speed up or beat harder, with higher force
of contraction, or maybe relax more quickly. So basically what
I'm telling you, these are the
sympathetic nerves. And of course, I
should also draw in the parasympathetic nerves. So these are going to tell
the heart to slow down and also going to increase
the delay in the AV node. And these are the
parasympathetic nerves, primarily the vagus nerve. You might hear that
word too, vagus nerves, which is basically
the actual name of the nerve itself. But they are
parasympathetic nerves. Now, you have information
flowing from the brain down to the heart. But you also have information
flowing from the heart up to the brain. So, information is going
up as well as down. So what would be an example
of information going up? Well, you can imagine
that there might be volume receptors, right? So we know that the brain
needs to know about the volume status. And in the right atrium, there
are some volume receptors that basically stretch. And once they stretch,
they tell the brain that there's a lot of blood. Or if they're not
stretched, they tell the brain that
there's not a lot of blood. And this really helps
with autoregulation of blood pressure. So if you want to regulate
your blood pressure, you've got to have
some information. So autoregulation
of blood pressure. So basically, the whole
point of me saying all this is that there's a lot of
nerves going back and forth between the brain and the heart. Now, let's say this person that
I'm describing tragically dies. They die. And they're wish was
to donate their heart. And so, over here we
have a heart recipient, someone that is interested
in getting a heart. Let's say that their
heart is not working well or whatever the
situation may be. They're actually
hoping to get a heart. So this person is looking for
a heart, and this person died and their wish was
to give a heart. So, let's show that actually. Let's show the
heart moving over. Let's say that this person's
heart gets sent over to the person on the right. So now their heart
gets sent over here. So all is well. And this person's actually
obviously very happy that they got a heart. This is obviously a big deal. Let's see if we can do this. There we go. This person's going
to be smiling, right? And I should probably erase
all these little nerves. But this brings up
a really good point, because if the nerves are not
coming over-- which they're not, it's just the heart-- then
can we regulate all the things that we know that
nerves help us regulate? Can we, for example, tweak
or change the heart rate if needed? Or can we change the force
of contraction if needed? Are any of those things going
to be able to be changed, or is this heart
basically now always going to be in one status, always
just beating at one rate, pumping it with one force,
is it ever going to change? Is there any way anything
can change this now that the nerves
are not connected? Well, the first thing is
that there is some evidence that nerves can reconnect
from the new body. But that would take
a long, long time. So in the short term,
what is the answer? Well, you have a
couple of glands. You have adrenal
glands sitting here. And these glands are sitting
literally above the kidneys. So these are the adrenal glands. And you also have thyroid gland. So these are the adrenal
glands and this is your thyroid up here. This is your thyroid kind
of in your neck region. So these are hormone producers. The thyroid gland,
the adrenal glands, they're going to be
producing hormones. And those hormones
can affect the heart. So, one hormone could
be, for example, this would be a thyroid hormone. Down below, you might
have epinephrine. So another hormone, number
two could be epinephrine. This comes from the adrenals. So you can see that
basically there are hormones that are
going to affect the heart. Over here in the first case,
when the heart was over here, you're getting rapid
changes, right? Very, very quick. But as compared to
what we were getting, this is going to be a little bit
slower in terms of the response rate, because now
the hormone has to go through the bloodstream
and get to the heart. And it takes a
little bit of time. Whereas before with
the nerves, you're really getting changes as
fast as a nerve impulse, which is on the order of
less than a second. So definitely the response
rate is going to be slower. So your heart can change its
force of contraction and heart rate and conduction velocity. It definitely can change in
this new person with a heart transplant. But it will take a
little bit longer. And another thing that
will change it, in addition to just hormones, I want to
remind you, is medication. So let's imagine this person
is taking medications. And let's say these medications
have certain properties. Let's say they're taking
a calcium channel blocker. Let's say they're taking
a medicine that's a-- I should probably write meds
here-- calcium channel blocker. Well, you know that there are
calcium channels in the heart. And if you are
blocking them, then that's going to have an effect
on the force of contraction, let's say. And what if they're
taking a beta blocker? And beta refers to the
receptor for epinephrine and norepinephrine. So if they're taking
a beta blocker, they're really blocking the
effects of, in this case, epinephrine, right? They're blocking
epinephrine effects. So you can see how if the person
starts taking a medication or let's say they take a
few pills on a certain day, or their adrenal glands are
making more epinephrine, all these kinds of things are
going to essentially change how the heart works,
how fast it's working, how hard it's working. So they are going
to have changes. It's not like they don't have
changes in any of those things. But those changes are going
to take place on a slower time scale than what would have
happened in the person who has all the nerves connected.