hello everyone today we are going to
talk about mechanisms of breathing when
we inhale the air the air is going to
enter into our nasal cavity or into our
mouth but breathing through our nose is
way better than breathing through our
mouth so after the air enters into the
nose or the mouth it's going to enter
into the pharynx from there it's going
to travel into our larynx which is our
voice box and then into our windpipe
which is our trachea and then the
trachea is going to start branching out
into the bronchi branches and from there
it's going to enter into the lungs until
it reaches the alveoli and this is where
the gas exchange is going to take place
within our lungs before the air enters
our lungs it's going to get warmed up so
that actually the alveoli are not going
to be destroyed or damaged by the cold
air the air is also going to be
humidified and so the air reaches 100
percent humidity before it reaches our
lungs and it's also going to be filtered
so that again we trap dust particles
pathogens etc we filter them before the
air reaches your lungs now there are
muscles that are going to help us with
the process of inhaling and exhaling so
we've got our intercostal muscles we've
got our sternocleidomastoid even your
abdominal muscles are going to help you
especially when you are forcing yourself
to exhale more so if you force yourself
to exhale a lot of air you will notice
that your abdominal muscles tense up
because they are going to help you push
that air out of your lungs
also our diaphragm muscle is definitely
pretty important so when we inhale the
air the diaphragm muscle contracts and
it moves downwards so that it can give
your lungs room to expand when we exhale
the diaphragm muscle is going to relax
and it's going to push itself back up
our lungs are surrounded by a pleural
sac if we look at this image and we look
at this air filled balloon which is
going to represent our lung and then we
have another balloon right here this is
going to represent our pleural sac so
this balloon right here which is
representing our pleural sac you can see
that there is fluid inside of it and you
can see that this balloon is only made
up of one membrane but when it wraps
itself around the lung you will notice
that it kind of looks like it has the
two layers so if this is our lung right
here this part of the pleural sac that's
closest to the lung is going to be known
as the visceral pleura layer and then
the outer layer right here which is
going to be the one closest to the
thoracic wall this one is going to be
the parietal pleura layer in between the
two layers you're going to have a cavity
in that cavity is going to be filled
with fluid that pleural fluid is
important because it's going to act as a
slippery fluid that's going to prevent
those two pleural membranes from rubbing
against each other especially because
your lungs are inflating and deflating
all the time and so with inflation and
deflation without any fluid in there
those two membranes you're going to
start rubbing against each other and
that's definitely going to be painful
also that fluid in there is pretty
important because it's going to kind of
create like a vacuum effect and it's
going to help push your lungs tight
against the thoracic wall if your lungs
are not pushed tight against the
thoracic wall your lungs are going to
collapse now the pressure inside right
here so the pressure in between the two
pleura layers we refer to it as the
intra pleural pressure and the
intrapleural pressure is always lower
compared to the atmospheric pressure
it's about the really good three degrees
lower compared to the atmospheric
pressure if that pressure increases so
if that pressure becomes let's say equal
to your atmospheric pressure that would
be disastrous because then your lungs
will collapse if the intrapleural
pressure becomes higher compared to the
atmospheric pressure same thing disaster
because that would cause your lungs to
collapse so to prevent your lungs from
collapsing that intrapleural pressure
always has to be lower compared to the
atmospheric pressure our trachea and our
bronchi are aligned with
ciliated epithelium tissue and you can
see the cilia right here on the apical
surface of our epithelial tissue the
cilia are bathed in a watery
saline layer and above that watery
saline layer there is a sticky layer of
mucus and that sticky layer of mucus is
going to help trap most of the inhaled
particles
before it reaches your lungs the Cilia
are going to sway back and forth with an
upward motion so that they can move the
mucus towards the pharynx so if we have
cilia right on our trachea the
cilia is going to keep pushing those
particles in an upward motion until it
reaches your pharynx which is your
throat once it reaches your pharynx
we are either going to spit it out
or we are going to swallow those inhaled
particles and if we swallow it think to
go into your stomach and the condition
there is highly acidic so the high
acidity within your stomach is going to
break down those particles that watery
saline layer is actually very important
for the Cilia movement without that
watery saline layer the Cilia is
actually going to get trapped in the
mucus and it's not going to be able to
move and so if that happens the bacteria
is actually going to start to reproduce
and increase in number because they're
trapped and you're having such a hard
time actually moving them the
bacteria kinda starts to multiply and
that can cause long infections when we
inhale the air is going to enter into
our larynx then into our trachea and you
can see that the trachea starts to
branch out the more it branches out
inside of our lungs the more those
branches get smaller and smaller until
those branches connect to a bunch of
alveoli this is where the gas exchange
is going to take place so if we zoom in
that we have one of the older sac right
here which is made up of a bunch of
alveoli there
going to be a bunch of capillaries on
top of our alveoli so any oxygen that's
going to be within your alveoli so after
you inhale and the oxygen enters into
your alveoli and the alveoli are going
to get inflated with all of that oxygen
the oxygen is going to leave your
alveoli and enter into your capillaries
so that it can be moved into your
bloodstream your capillaries are also
carrying carbon dioxide so the carbon
dioxide in your capillaries will exit
the capillaries enter into your alveoli
so that we can exhale it out so as you
can see the oxygen and the carbon
dioxide gases are going to easily be
transported into and out of your alveoli
and so that's why we say this is where
the gas exchange is going to take place
and the reason why the gas exchange is
going to take place pretty fast within
our alveoli that's because our alveoli
it's very thin it's lined with simple
squamous epithelium tissue and your
type one alveolar cells are the ones
kind of make up the walls of our alveoli
we also have type 2 alveolar cells and
those produce what's known as a
surfactant and the surfactant
consistency wise it's kind of like soap
detergent that's going to be coating the
inside of your alveoli the surfactant is
actually pretty important in preventing
your alveoli from collapsing because if
your alveoli collapse then your lungs
are going to collapse so to explain how
the surfactant works if we zoom in on
one of the one of the alveoli
so singular we
refer to it as alveolus so let's say
that this is one alveolus right here
lining the inside of the alveolus we
actually have a layer of water and then
of course the inside of the alveolus
this is where you're going to have the
air so if we zoom in on the water
molecules right here so here are a bunch
of water molecules now the water
molecules are known to bind to each
other via a bunch of hydrogen bonds so
if we look at this middle water molecule
right here notice how this water
molecule in the middle is basically
binding to all of the water molecules
that surround it so you can see that
it's binding right here to this water
molecule right there and up and down and
you can see that this middle water
molecule right here those vectors that
are presented right here they're all
going to cancel each other out so the
one on the right and the one on the left
equal forces it's gonna cancel out up
and you know that top one and that
bottom one again equal forces they're
going to cancel out but if we go ahead
and look at this water molecule right
here you can send this water molecule
it's going to bind to the water molecule
on both sides on the right and on the
left and it's going to bind to the water
molecules on the bottom but it's not
going to bind to any water molecules on
the top because above that water
molecule we have air so what's going to
happen is that the right and left forces
right here those are going to cancel
each other out but then notice how this
force that's going downwards there is no
force that kind of
lies is it on the top and so what
happens is that since those are going to
cancel out all the force is actually
going to be headed downwards and that
creates what's known as a surface
tension so the force is going to be too
powerful kind of pushing that water
molecule downwards creating a surface
tension up at the surface right here so
all of these top water molecules they
are actually going to be pushing
downwards because again there is no upward force to kind of equalize it and so
that's what creates the surface tension
that's why when you look at the surface
of the water and you wonder why some
insects are actually able to walk on the
surface of the water because they are
very light those insects and they are
not breaking that surface tension so
what happens is we end up with surface
tension within our alveolus now that
surface tension as I said is going to
keep pushing downwards and it's actually
going to cause the alveolus to start
collapsing and so what happens is to
prevent the collapse of our alveoli due
to that surface tension of the water
within our alveolus type 2 alveolar
cells that produce a surfactant and the
surfactant what it's going to do is it's
actually going to that surfactant that
kind of like detergent like substance is
actually going to come and break that
surface tension because that surfactant
is going to start as you can see like
those
circles that I'm drawing it's
actually going to kind of push itself
between the water molecules and it's
actually going to break that surface
tension and so when that surface tension
is broken that alveoli are not going to
collapse now when do we produce that
surfactant we produce a surfactant by
the 34th week of pregnancy and so that's
why if babies are born premature
and they have not produced their surfactant yet what's
going to happen is their lungs are going
to collapse and so therefore premature
babies are going to have to get hooked
up to ventilators because they are not
producing their own surfactant yet and
so another thing they could do is other
than hooking them up to ventilators now
they have like surfactant they actually
spray again to prevent those premature
babies from having collapsed lungs and
so the surfactant what it does is it
lowers the surface tension with it
within your alveolus preventing your
alveolus from collapsing the
relationship between pressure and volume
is inversely proportional
so Boyle's law is basically explaining
that inverse proportional relationship
between pressure and volume that means
that as the pressure increases the
volume is going to decrease and as the
pressure decreases basically the volume
increases so you can explain that let's
say that
you have this beaker right here and you
have some particles within that beaker
and so you can see that the volume here
it's pretty large and so the
pressure inside of that beaker is not
going to be high because those particles
are not going to be bombarding against
each other or bombarding against the
walls because they actually have room to
move but what happens is if we go ahead
and start decreasing the volume within
that beaker so notice how the volume
decrease now there isn't enough room for
those particles to move and so they're
going to start bombarding against each
other they're going to start bombarding
against the walls of the beaker and so
the pressure in here is actually going
to start rising you can see that as the
volume decreased the pressure increased
and so that's again Boyle's law now
dalton's law is basically explaining the
partial pressure of a gas so when we
think of air air is made up of a mixture
of gases so like oxygen gas nitrogen gas
etc they're all mixed in together now if
you want to actually calculate the
partial pressure of a certain gas what
you do is take the whole entire
atmospheric pressure which is around 760
millimeters mercury
that's the units that we use for for gas
pressure and you multiply that
atmospheric pressure by the percentage
of the gas in the atmosphere so let's
say that I want to figure out the
partial pressure of the oxygen gas in
the air so I take my atmospheric
pressure which is 760 and I
multiply it by how much oxygen do I have
so if I say that the percentage of
oxygen in the atmosphere is around 21%
you multiply that by 760 and so that
would tell you that the pressure of the
oxygen in the atmosphere is around 160
millimeters mercury
so dalton's law is basically a way to
calculate the partial pressure of gases
in the atmosphere we also have to
account though if the atmosphere has
water vapor so if basically the air is
humid which means there is water you
have to take that into account and you
have to subtract the pressure of water
so let's say that your air is pretty
humid and so it has water you have to
subtract the pressure of water from the
atmospheric pressure so that you can
calculate that partial pressure of a
certain gas so if the atmospheric
pressure one more time is 760 and let's
say that the pressure of the water is 24
millimeters mercury again this is going
to be given so let's say they tell you
that the air it's 100% humid and the
pressure of the water is around 24 you
have to subtract that 24 from the
atmospheric pressure and then you
multiply that by the partial pressure of
the gas that you are trying to calculate
and so the pressure the partial pressure
of oxygen in dry air is around 160 but
notice how the partial pressure of
oxygen in humid air it's 155 and the
reason why it's less because we have
subtract out the pressure of water so
that's dalton's law it helps you figure
out the partial pressure of gases now if
we look at this image right here we are
going to talk about our lung volumes and
capacities so we have what's known as
the tidal volume that's basically around
five hundred mils for both females and
males and that's the amount of air that
we normally inhale and we normally
exhale without without putting any extra
force so right here when you inhale you
consider the volume inside of your lungs
it's going to increase because you're in
taking air and so that upwards wave is
going to represent inhalation and then
as we go downwards that's going to
represent exhaling so we normally inhale
about 500 mils of air and we normally
exhale around 500 mils of air and that's
usually traced and using what's known as
spirometer and now we have digital
spirometers that can easily
calculate those volumes for us now if
you force yourself let's say that you
already inhaled the 500 mils of air
right so you normally you took the
normal breath but then you went and you
went ahead and you forced yourself to
even inhale even more air that's going
to be known as the IR V or the
inspiratory reserve volume and it
differs between males and females you're
going to notice that males they will
have actually larger lung capacities
they're able to intake more air compared
to females now
if you force yourself to exhale more air
out that's going to be known as the
expiry reserved volume now even if you
force yourself to exhale and you feel
like that's it I can't exhale anymore
does that mean you've exhaled all the
air out of your lung
no you actually still have some air
inside of your lung and we refer to it
as the residual volume so the residual
volume is not going to be exhaled out
actually we don't want to exhale the
residual volume because otherwise your
lungs are going to collapse so there's
always a bit of air within your lungs
known as the residual volume to prevent
your lungs from collapsing
now capacities are basically where you
add a bunch of volumes together so your
total lung capacity if I want to figure
out you know my total amount of air that
my lungs can actually intake and exhale
out I would basically take my tidal
volume and I would add my inspiratory
reserve volume expiratory reserve
volume and my residual volume so that's
going to be my total lung capacity your
vital capacity is basically everything
except your residual volume so it's your
tidal volume plus your IRV plus your
ERV that would be your vital capacity
and as you can see the tidal volume for
both me females and males it's about the
same but then the IRV and the ERV are
going to be different and so therefore
the lung capacity is are also going to
differ between males and females
if we look at those three graphs right
here this bottom graph is representing
the volume of air inside of our lungs
this middle graph right here is
representing the pressure the
intrapleural pressure which is the
pressure between the visceral and
parietal pleura layers and then this top
graph is representing the alveolar
pressure so the pressure inside of our
lungs within our alveoli if we take a
look right here at the alveolar pressure
we said that the atmospheric pressure so
the pressure of the air is around 760
millimeters mercury but to simplify
things we are going to say that the
atmospheric pressure is 0 and you can
see right here you know the 0 is going
to represent the atmospheric pressure
and then you can see if the pressure
increases we are going to represent it
by a positive pressure and then if the
pressure decreases below the atmospheric
pressure we are going to represent it by
negative numbers so if we take a look
right here at time 0 you can see that
there is no flow of air so you can see
right here of the volume within your
lungs it's not changing you can also see
that the pressure in your intrapleural
region it's negative 3 again that
that just means that the pressure there
is below your atmospheric pressure by
around 3 points so that's why we are
representing it by negative 3 and then
you can see that the alveolar pressure
is at 0 so the thing is when your
alveolar pressure is equal to the
atmospheric pressure
as you can see right here they're both
at zero no air is going to flow so no
air is going to enter your lung no air
is going to exit your lung
there is absolutely no air flow when the
atmospheric and alveolar pressure are
equal and you can see that at all times
the intrapleural pressure must always be
below your atmospheric pressure
otherwise your lung is going to collapse
so if we look right here at time zero to
two seconds when we are inhaling when we
are inhaling our muscles are going to
start to contract like your diaphragm
muscle your intercostal etc and you will
notice that your thoracic volume starts
to increase
so we are starting to inhale you notice
that the volume is increasing within
your lungs
if you remember Boyle's law we said that
the pressure and volume are inversely
proportional so as the volume increases
you will notice that your alveolar
pressure is going to decrease and you
can see that it's decreasing beyond the
atmospheric pressure your intrapleural
pressure is also going to decrease as
well so as the pressure starts to
decrease the air is going to move from
high pressure to low pressure so if the
pressure inside of your lungs it's now
below the atmospheric pressure the
pressure in your atmosphere is now
higher that's why the air is going to
move into your lungs so when we inhale
the reason why when we inhale the air
moves into your lungs
because now the pressure inside of your
lungs it's lower compared to the
atmospheric pressure as the air starts
to flow into your lungs the pressure
eventually is going to start to increase
so you can see right here the pressure
actually starts to increase until your
thoracic cage stops expanding and when
the pressure as you can see starts to
increase within your lungs and it
reaches one more time to zero meaning
that now it's equal to your atmospheric
pressure
no more airflow so you can see right
here the air is not flowing anymore
and then at the end of inspiration our
muscles are going to start to relax and
your diaphragm also starts to relax and
return back to its relaxed position and
then we move into the expiration stage
so kind of like right here from 2 to 4
seconds we are going to be exhale Inc
and so you can see that as we exhale the
volume within our lungs starts to
decrease because we are pushing all of
that air out of our lungs and then as we
said as the volume that decreases the
pressure is going to further increase
within our alveoli and so as we said one
more time air moves from high pressure
to low pressure so when you are exhaling
and your alveolar pressure increases
above the atmospheric pressure so you
can see right here it's above
atmospheric pressure the air is going to
be pushed out of your lungs from high
pressure to low pressure and then
you can see right here your intrapleural
pressure even though it's increasing you
notice that it's still below your
atmospheric pressure so the intrapleural
pressure always has to be
sub-atmospheric meaning that it always
has to be below the atmospheric pressure
otherwise your lungs are going to
collapse and then you can see that the
cycle is basically going to keep
repeating itself and whenever the
pressure of your alveoli is equal to the
atmospheric pressure basically no air is
going to flow either in or out of your
lungs this image right here is showing
you that there's always a cohesive force
within your intra pleural fluid causing
your lung to adhere to the thoracic cage
and that's important because if your
lung is not adhere to the thoracic cage
the lung is going to collapse and there
is a combination constant combination of
an outward pull by your thoracic cage
and an inward pull by your lungs trying
to kind of recoil back to their original
shape and that canna creates a sub
atmospheric pressure right here within
your intra pleural fluid that's why as
we said that pressure when we looked at
the previous image it's around three
degrees lower compared to the
atmospheric pressure and we said that it
always has to stay below the atmospheric
pressure what happens if someone let's
say gets
or one of your ribs actually cracked and
pierced your pleural fluid or if someone
as I said get stabbed for example and
now you've kind of pierced that pleural
fluid what happens is air is going to
start entering into that space into that
intra pleural space and what happens is
when air enters into that intra pleural
space the pressure within your intra
pleural space is actually going to start
to increase and so when the pressure
increases your lung is not actually
going to be stretched anymore towards
your thoracic cage and as you can see
the lung kind of starts to pull away
from the thoracic cage and what happens
when the lung kind of pulls itself away
the lung is going to collapse and we
refer to that as pneumothorax

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