the main job of the lungs is gas
exchange pulling oxygen into the body
and getting rid of carbon dioxide
normally during an inhale the diaphragm
contracts to pull downward and the chest
muscles contract to pull open the chest
which both help suck in air like a
vacuum and then during an exhale the
muscles relaxed allowing the lungs to
spring back to their normal size which
pushes air out
when you breathe in air flows to the
nostrils and enters the nasal cavity
which is lined by cells that release
mucus that mucus is salty sticky and has
lysozymes
which are enzymes that help kill
bacteria nose hairs at the entrance of
the nasal cavity get coated with that
mucus and are able to trap large
particles of dust in pollen as well as
bacteria forming tiny clumps of boogers
the nasal cavity is connected to four
sinuses which are air-filled spaces
inside the bones that surround the nose
called the paranasal sinuses there's the
frontal ethmoid sphenoid and maxillary
sinus those sinuses help the inspired
air to circulate for a bit so it has
time to get warm and moist
they also act like tiny echo chambers
that help amplify the sound of your
voice and this is why you sound so
different when you plug your nose or if
they get clogged with mucus during a
cold so that relatively clean warm and
moist air goes from the nasal cavity
into the pharynx or throat the region
connecting the two is called the
nasopharynx and the part connecting the
pharynx to the oral cavity is called the
oropharynx the soft palate which is the
softer portion of the roof of your mouth
behind the hard palate which is the part
you can feel with your tongue and the
pendulum like uvula hanging at its end
move together to form a flap or valve
that closes the nasal pharynx off when
you eat to prevent food from going up
into the nasal pharynx finally there's
the laryngopharynx the part of the
pharynx that's continuous with the
larynx or the voice box
up to this point food and air share a
common path but at the top of the larynx
it's a spoon shaped flap of cartilage
called the epiglottis which acts like a
lid that seals off the airway when
you're eating so that food can only go
one way down the esophagus and towards
the stomach if anything other than air
gets into the larynx then you have a
cough reflex that kicks it right back
out
now once air makes its way into the
larynx it then continues down the
trachea or windpipe which splits into
two main stem bronchi the point at which
they split is called the Carina it then
enters the lungs and the right lung has
three lobes the upper lobe middle lobe
and lower lobe the left lung just has
two lobes the upper lobe in the lower
lobe the right mainstem bronchus is
wider and more vertical than the left
which is why if you accidentally inhale
something big that can't get coughed up
like a peanut it's more likely to go
into the right lung than the left the
main stem bronchi then divide into
smaller and smaller bronchi the trachea
and the first three generations of
bronchi are all pretty wide and used
cartilage rings for support
now taking a look at a cross-sectional
chunk of this trachea there is also a
layer of smooth muscle which has nerves
of the autonomic nervous system in it
the autonomic nervous system is made up
of two basic types of nerves sympathetic
nerves which are involved in
fight-or-flight mode like running from a
turkey and parasympathetic nerves which
are involved in the rest and digest mode
like eating ice cream on the beach
smooth muscle along the trachea and the
first few branches of bronchi have
beta-2 adrenergic receptors going back
to that turkey when you're running the
sympathetic nerves stimulate those
beta-2 adrenergic receptors and this
increases the diameter of the Airways
allowing more air to get in
but those same Airways also have
muscarinic receptors which can get
stimulated by parasympathetic nerves
causing a decrease in the diameter of
the Airways the large Airways are lined
mostly by ciliated columnar cells and a
handful of goblet cells which get their
name from looking like a wine goblet and
these guys secrete mucus that mucus
helps trap particles and then the
ciliated columnar cells beat
rhythmically to move the mucus and any
trapped particles from the air towards
the pharynx where they can either be
spit out or swallowed this mechanism is
known as the mucociliary escalator
after the first three generations of
bronchi though the Airways get more
narrow called bronchioles meaning little
bronchi and these can stay open without
the need for cartilage air is conducted
through smaller and smaller bronchioles
for about 15 to 20 generations and
collectively these are known as
conducting bronchioles these conducting
bronchioles receive oxygenated blood
from the bronchial arteries the walls of
those conducting bronchioles are also
lined by ciliated columnar cells and
mucous secreting goblet cells as well as
a new type of cell called a club cell
these Club cells secrete
glycosaminoglycans which protect the
bronchial or epithelium these guys can
also transform into ciliated columnar
cells so they help regenerate and
replace damaged cells if needed
now all these cells the bronchioles
receive oxygenated blood from the
bronchial arteries of the systemic
circulation which is important to keep
in mind for later
the last part of the conducting
bronchioles are the terminal bronchioles
and then after that air gets the
respiratory bronchioles which are unique
because they have tiny outpouching x'
that butt off from their walls these
outpouching x' are called alveoli and
there are about 500 million of them in
the lungs
eventually the respiratory bronchioles
end when there's nothing but alveoli and
at that point the airway is called an LV
ole or duct rather than a respiratory
bronchial and this is the final
destination of the inhaled air the
alveolar wall has a completely different
structure than the bronchioles there are
no cilia or smooth muscle and instead
the walls lined by thin epithelial cells
called pneumo sites most our regular
pneumo sites called type 1 pneumo sites
but some called type 2 pneumo sites have
the ability to secrete a substance
called surfactant surfactant helps
decrease the surface tension within the
alveoli and therefore helps keep them
open
just like the club sells the type to
pneumo sights are capable of
transforming into type one pneumo sights
so they can also help regenerate and
replace damaged cells finally if a tiny
particle ever makes it deep into the
lungs
there are alveolar macrophages that can
gobble it up and then physically move up
to the conducting bronchioles where they
can ride the mucosal iary escalator all
the way up to the pharynx to be either
coughed up or swallowed down free from
particles the inhaled air is now in the
alveolus surrounded by mostly type 1
pneumo sites on the other side of the
numa sites are endothelial cells that
line the capillary walls which is what
holds the blood this time though that
blood comes from the pulmonary arteries
and is deoxygenated the pneumo sites and
the capillaries are glued together with
a protein layer called the basement
membrane so the alveolar wall the
basement membrane and the capillary wall
is really all that separates the air
from the blood and this is called the
blood gas barrier at this point carbon
dioxide diffuses out from the
deoxygenated blood and into the air of
the alveoli which then gets breathed out
and with each breath in oxygen enters
the alveoli and freely diffuses into the
blood that freshly oxygenated blood then
heads off to the pulmonary veins the
heart and then to the body's tissues all
right as a quick recap the respiratory
system facilitates gas exchange oxygen
in the air is inhaled and makes its way
through the pharynx larynx trachea large
upper Airways conducting bronchioles
respiratory bronchioles the alveoli and
finally the capillary to be sent to the
body's tissue then carbon dioxide makes
the reverse journey to eventually be
exhaled into the world
what's happening guys thanks for
watching that video on respiratory
physiology if you want to do a deeper
dive into that topic for sure head over
to osmosis org we've got a bunch of
flashcards quiz questions and scheduling
tools essentially anything a student in
medicine needs so if you're interested
for sure head over and make an account
otherwise I have some awesome news for
you guys I got this in the mail the
other day which is like the YouTube a
hundred thousand subscribers silver
plaque pretty cool but really I just
want to give a huge thank you to you as
the viewers and the subscribers because
you're kind of the reason we're still
making videos so so really thank you for
your support these last year or so and
also huge thank you to Kyle and Rishi
who are the other two that I've sort of
been around since the beginning of the
mostess channel thanks to you guys
because this is like just as much theirs
as it is mine and that's kind of all I
got for you guys until next time bye
you