在本课程中，学生将学习认识和应用说明人体九个器官系统中整体人体机能（作为完整有机体）的基本概念。
解剖学和力学
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來自 Duke University 的課程
人体生理学导论（中文版）
86 個評分
從本節課中
呼吸系统
此模块介绍呼吸系统。 在这些课中，我们将探讨如何将空气吸入肺中、通气中气道阻力、氧气和二氧化碳在肺和组织间的输送，以及呼吸调节等课题。 视频中提供了几个肺功能演示！
與講師見面
Jennifer CarbreyAssistant Research Professor
Department of Cell Biology
Emma JakoiAssociate Research Professor
Department of Cell Biology
Welcome back.
This is our first on several videos about the respiratory system,
and so we're going to start off talking about the general
anatomy of the lung and then some of the mechanics of
breathing, how we get air in and out of our lung.
Obviously, one of the main roles of the respiratory system
is to bring in oxygen so that we can do oxidative
metabolism, and then to remove the carbon dioxide that we produce.
However, we're also going to be talking about
the very important role of the respiratory system
in regulating our pH, and then also keep in mind that because we are bringing in
so many liters of air a day, ten thou-, around, roughly 10,000 liters a day,
and our lungs have such a large surface area, that the, this is a major site
of concern for our defense system, for our immune system.
And so the respiratory system is going to have
certain strategies that it uses to protect itself from pathogens.
And that's something we're not really going to focus
on, but keep in mind that that is
an important thing that, an important factor that
the respiratory system has to keep in mind.
Now, we're going to see many similarities of the respiratory system to
the cardiovascular system because, again, we're going to be talking about flow.
And so we're going to be talking about pressure gradients and that the
amplitude of that pressure gradient or that the amount
of the pressure gradient is going to be important, as well as the resistance.
And again, the, the resistance is going to be related to the radius of
the tube, and the radius is going to be to the 4th power.
So the radius is going to make a
huge difference in the resistance of the system,
and again, we'll be addressing that in similar
ways that we did for the cardiovascular system.
So just in a very low-mag view of the anatomy of the respiratory system,
it's going to start with the nose and mouth
where air enters the body, and then it's, the air
is going to enter the trachea, which is going to be
a tube that is, got surrounded by rings of cartilage.
And then the trachea will branch into bronchi
that are also surrounded by cartilage, and then
those will continue to branch more and more
until we get to what's called the respiratory
part of the lung, which we'll be talking about in a moment.
And then keep in mind also, we're going to be talking about the diaphragm, which is
going to be sitting underneath the lungs, and which is going to be skeletal muscle.
So we will be talking about the respiratory system by
dividing it into two parts. One is going to be the conducting part
which is going to contain about 150 mills of air.
And as its name suggests, one of its main roles is to conduct or bring
air into the main part of the lung that is going to be responsible for exchanging
gas with the blood.
So that is certainly one of the roles of the conducting portion of
the respiratory system, is to distribute air into the rest of the lung.
The conducting portion is also going to warm and moisten the air,
and we'll talk about that a little bit more in future sessions.
And it's also going to have a major role in cleansing
the air.
So again, this gets into the idea that the lung has got to
be concerned about all these liters and liters of air that it's bringing in.
And so the conducting portion is going to
cleanse the air using what's called mucociliary transport.
Which is going to be when some cells
lining the conducting portion, the trachea and the bronchis,
are going to be producing the mucus and then that will
trap debris and then there will be other cells that have
cilia that then take that mucus that it contains the debris
and beats it up towards the entry way of the respiratory
system. So that's the mucociliar transport
system where we have mucus and cilia that are going to work
together to remove particular matter and pathogens.
The other aspect of the conducting system
is that in particular the bronchioles, very similar
to the way the arterioles controlled the flow
through the system based on changing its diameter.
The bronchioles are going to also have smooth muscle
around them which is going to help determine how
easily air flows into the lung through changing their
amount of contraction or relaxation of that smooth muscle.
So, those are the roles of the conducting portion of this system.
Then the largest volume is going to be in the respiratory portion of
the respiratory tract, which is going to be about three
liters, kind of at rest, where we're going to have gas exchange.
Where the, and it's going to be made up of alveoli that have a very
thin epithelium that allows for diffusion of gases between
the alveoli and the capillaries that are going to receive and
dump off gases.
So, lets talk a little bit more about the structure of the alveoli.
So in this diagram, we have three alveolar sacs.
So each one of these structures would be an alveolar sac, and you can see that it's
a spherical structure that is then made up of smaller spheres and each
of these smaller spheres is an alveolus.
So the alveolar sack is made up of lots of different alveoli.
And the inner surface of these alveoli is what's in contact with the air.
And then you can see how the outer surface is just covered in capillaries.
The inner surface of the alveoli makes up a large surface area.
So it's about 70 square meters in the lungs, which is obviously
going to allow for a lot of gas exchange since we have a large surface area.
And that surface is going to be comprised mostly of type one cells
that are going to make the surface of the alveoli that is in contact with the air.
And these cells are going to be very flat cells.
So they're going to be the epithelial cells of the alveoli.
They're very flat and thin so that the air does not have
to go a very long distance to cross the type one cells.
In between the type one cells will by type two cells that
don't cover as much of the surface area of the alveoli,
but they're there as stem cells and as cells that produce surfactant.
And we'll be talking more about surfactant in the future.
So you can see how we have this thin epithelium and then lots of capillaries
on the other side of it to exchange the gas between the air and the blood.
We're going to move now to talking a little bit more about
ventilation and how we get air in and out of our lungs.
And it's going to be really important to remember that the way
that we get air into our lungs is called negative pressure breathing.
So basically, what we're going to do is we are going to take our diaphragm, which
is a dome-shaped muscle, and contract it. And so, it's skeletal
muscle, and if you contract it, that's going
to make it shorter, and it's going to become flatter.
So as it becomes flatter, then that is going to cause the chest wall to expand.
And as that chest wall expands, then that
is going to lower the pressure in the lungs.
So you have negative pressure in the lungs, and that means that air is going
to flow into the lungs.
So the diaphragm is what's going to be very important when we're just
doing normal activities like sitting and watching
me lecture where you're somewhat at rest.
You're going to contract your diaphragm to inhale and
then you're just going to relax your diaphragm to exhale.
And we'll be talking more about this. But if for
instance you're exercising you're going to want to take a deeper breath.
And you are going to want to breathe more quickly.
And that's when you bring in muscles of the rib cage that are
going to kind lift the ribs, kind of like a handle on a bucket.
And you lift it.
And that's going to increase again the volume in the lungs.
And then you can also use when
you're trying to exhale quickly, many other muscles
of the chest wall, as well as the abdomen.
So depending on the type of breathing you can do, you're doing, you might use
more muscles, but very often just in
normal rest breathing, you're using primarily the diaphragm.
The other thing that, to keep in mind, and we'll be
talking much more about this, is the reason why you can kind
of just relax your diaphragm, and everything just com,
compresses, the chest wall gets smaller on its own, is because of the
elastic recoil of the lung that makes the lung want to
get smaller, and that's what helps in that passive exhalation process.
And we'll be talking more about that in future sessions.
So here's another view of this,
where if we contract the diaphragm, we're going to expand
the chest wall. That's going to, because of
Boyle's Law, cause the pressure in the lung to go down.
And that means that we're going to have a greater pressure out
in the atmosphere and that means air is going to flow in.
So that's inhalation.
Negative pressure breathing. And air is going to enter when the
pressure outside in the atmosphere is greater than the pressure in the alveoli.
So P capital A refers to the pressure in the alveoli.
We're going to be using this abbreviation a lot, so it's good to get used to
it. When you inhale and
then you often kind of pause before
you exhale, then very rapidly the pressure will
equilibriate between the alveolar pressure and the atmospheric,
-phere pressure, and so, flow will become zero.
So in between breaths, that's what's going to happen under most circumstances.
When we expire, then that's going to be
usually passive under normal conditions, and that's just
when the thoracic cavity, the chest wall, and
the lung are going to return to their normal dimensions.
And as that happens so the diaphragm is going to become dome-shaped as it relaxes.
That's going to increase the pressure in the lungs and that will make
its pressure greater than atmospheric pressure and so air will flow out.
So that's what's here where air leaves when atmospheric
pressure is less than the alveolar pressure.
So let's talk about ventilation, which is going to be
this exchange of air between the atmosphere and the lungs.
And we can talk about a ventilation cycle,
which is going to be one inhalation and one exhalation.
And we'll be talking some about the frequency of
ventilation, how many breaths per minute are you taking.
Often it's going to be between ten to 18 breaths a minute.
We'll also be talking about tidal volume, which is how much air you're inhaling
or exhaling and that's going to often be about a half a liter per breath.
And so using the tidal volume and
multiplying it by the frequencies, frequency of
breathing, then we can determine a minute
ventilation, how much air are you bringing into
your respiratory system each minute.
And so if you're breathing half a liter a minute, ten
times a minute, then that's going to be about five liters a minute.
Keep in mind, and we'll be talking about this some, that the depth and
the rate of breathing can change, and
this can dramatically increase air flow, twenty-fold.
And then blood flow
can increase three-fold to the respiratory system.
So during heavy exercise we can make
a huge adjustment in basically the minute ventilation.
However, if you are going to do that,
you are going to need to have active exhalation.
You don't have time to let everything slowly
relax and let the recoil of the lungs happen.
You are going to need to have to be able to squeeze
out that air so that you can quickly take another breath in.
And so that will require those abdominal
muscles and the intercostal muscles between the ribs.
So, let's finish this up by just reviewing what we've talked about
where we're going to have this huge interface for gas exchange with the lung.
And we've talked about how it's going to contain a conducting zone,
which is what we're going to call dead space because it can't exchange gas.
And that's going to have an alveolar space, which is the respiratory zone,
and we'll be talking more about that. We've talked about some of the basics of
how we use negative pressure breathing to get into the lung, and then how we exhale.
And then how we're going to have passive exhalation if we're at rest
but then during exercise that we're going to need active exhalation.
And that one reason why we can have passive
exhalation is because the lungs want to recoil, and
so that's going to help drive that process, and
we'll be talking more about that in future sessions.
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