hi let's talk about ventilation and the muscles of respiration ventilation is the movement of air
in and out of the lungs and this is controlled by controlling the volume of the thoracic cavity and
that's controlled by the muscles of respiration now if you have a chemistry background you recall
that Boyle's law is that pressure times volume is equal a constant and if we are to rearrange
that we would see that the relationship between pressure and volume is inversely proportional so
what this means is if we want to move air into the lungs we need to make the pressure of the
pleura where the lungs are contained lower than atmospheric pressure so we have to increase the
volume so that we can decrease the pressure so there are two processes at play here the
first would be inhalation and the other would be exhalation so inhalation is largely controlled by
the diaphragm the diaphragm sits between the thoracic and abdominal cavities as a domed
muscle and when it contracts it moves inferiorly now regular or just tidal breathing just sitting
there watching a lecture you're moving maybe about 500 to 700 milliliters of air in and out of your
lungs and that's all compliments of the diaphragm so as you inhale that's an active process of the
diaphragm contracting and then as the diaphragm relaxes that leads to exhalation but you can also
have forceful inhalation with forceful inhalation you could bring a couple of other muscles to bear
so namely there are external intercostal muscles these are on the ribs and if you were to put your
hands on your rib cage and take a very deep then you'd be able to feel your ribs expand outwards
and that expansion outwards is compliments of these external intercostal muscles you also
have muscles such as your sternocleidomastoid muscles and your scalene muscles which you can
see over here going down to the first and that the second rib respectively these are going to
pull up on those first few ribs and both the manubrium of the sternum so as to help increase
the volume of the thoracic cavity and encourage air to move in also muscles such as pectoralis
minor and serratus anterior can come into play as well now exhalation or I should say forceful
exhalation is compliments of a couple of different pairs of muscles so first of all on the ribs you
have internal intercostals so if you were to again put your hands on your ribs and take a
deep breath you can feel the ribs expand and then you can and you can feel those sharp contractions
of your thoracic cavity also are your abdominal muscles so your external oblique your internal
oblique transversus abdominus rectus abdominis these are muscles that are helping to control
the anterior and lateral abdominal walls and as they contract they decrease the volume of
the abdominal cavity increasing the pressure and what that does is that applies pressure
to the diaphragm for exhalation and so we have a means to move air in and out of the lungs by
controlling that space of the the thoracic cavity by these muscles of respiration finally your lungs
exist in sacs called the pleura so if you were to divide up the thoracic cavity you would have two
pleura which are lateral and then central you would have the mediastinum and the mediastinum
would be where the heart would sit within the pericardium so these pleura represent spaces
into which the lungs can expand and then contract as they relax and then the space between the lung
and the pleura would be the pleural cavity now just like the peritoneum or the pericardium or
other instances there are both visceral pleura and parietal pleura the visceral pleura is the pleura
that is immediately adhered to the surface of the lung so everything that I'm outlining now would be
visceral pleura on this side we have a collapsed lung so someone must have had a pneumothorax or an
induction of air into that pleural cavity and so this lung has collapsed and that's a more
exaggerated way of seeing the visceral pleura the parietal pleura lines everything else all
along the thoracic cavity to surround the lungs and that's going to form the maximum extent of
the pleural sac now that parietal pleura has a couple of specializations and I've color-coded
these for you so there's diaphragmatic pleura diaphragmatic pleura actually sits on the
diaphragm there's also costal pleura costal pleura is behind the thoracic wall so behind
the ribs or the costi cervical pleura up here in the cupula so that's adjacent to the root of
the neck and then a little bit of mediastinal pleura between the lungs and the mediastinum
and so to review we have diaphragmatic pleura costal pleura cervical pleura and mediastinal
pleura and then those are the parts of the parietal pleura and then we have visceral
pleura adhered to the lungs directly so we've talked a little bit about ventilation and how
through contracting the muscles of respiration we're able to either move air into or out of
the lungs and we've talked about the pleural sacs and the various linings of them thank you