![]() ![]() ![]() Alveoli at the apex of the lung are already extended and therefore have limited capacity to take in more air their resting volume is also close to the flat part of the compliance curve (figure 4.3), so they are more difficult to inflate. This has ramifications on where air entering the lung goes and how ventilation is distributed across the lung (more on the implications of this in chapter 13). Gravity acts similarly on the resting lung with less weight below the alveoli near the base, there is less force pulling the alveoli there open, and the basilar alveoli are smaller than those at the apex. The weight pulling the coils open becomes less further down the slinky, so the distance between the coils is less nearer the bottom. The lung acts just the same alveoli at the top are extended at rest, while those at the base have a smaller volume. As you travel down the slinky the coils are less and less extended as less and less weight below pulls on them. The coils near the top of it are pulled far apart because of the weight of the slinky below the top. So at the apex of the lung alveoli tend to be large because of the more negative intrapleural pressure, while at the base, alveoli are less extended because of the less negative intrapleural pressure. If an analogy would help, look at this slinky being held up (figure 4.4). As you know from the previous chapter, intrapleural pressure determines alveolus size (figure 4.3). Simply because of gravity, therefore, we have a distribution of intrapleural pressures. As we descend down the lung the mass below each point becomes less and less, so the pull on the pleural space declines, and we see intrapleural pressure become less and less negative.įigure 4.3: Interaction of lung volume, compliance, and distribution of ventilation. \)Īlveoli at the apex (top) of the lung have a substantial amount of lung tissue below them for gravity to act on, so there is a large force pulling the lung away from the pleural space here and hence at the top of the lung intrapleural pressure is more negative. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |