Love this video and your approach in life!

How'd the MCAT go, doc?

Increased pressure of inflation will draw water from the capillaries into the alveoli. Therefore, by decreasing pressure (increasing compliance) surfactant will prevent pulmonary edema, and even possibly reduce the edema in some cases. The edema is simply water moving along pressure gradients. Reduce the gradient and reduce the edema.

Mike Birkhead Mike, thanks for the response, but I'm not sure that higher intraalveolar pressures necessarily pull water into the alveoli per se. I think what probably happens in situations of surfactant depletion, collapse of alveoli from the increased surface tension then results in a reduction in the pulmonary interstitial pressure as adjacent alveoli tug at the interstitum from opposite directions as they collapse. It's this reduction in interstitial pressure that creates a pressure gradient favorable for fluid loss out of the capillaries. The net result is that there is more fluid in the interstitium, not necessarily in the alveoli - though this is still referred to as pulmonary edema, and would essentially have all of the same effects of fluid in the alveoli (e.g. hypoxemia with elevated A-a gradient, lower lung compliance, etc...) See: www.ncbi.nlm.nih.gov/pubmed/1399997 In 15 years, I've never once heard this come up on the wards; I would imagine that the clinical relevance of this specific issue (i.e. surfactant loss leading directly to pulmonary edema) is probably quite low. Please feel free to reply again if you still have different thoughts. This is me hypothesizing, not me stating known physiology facts.

Eric's Medical Lectures I don't have any time in the "Wards", I'm a first year medical student. The basis of my statement came from reading what we call a "SuperObjective" Which is a compilation of several students study guides (usually four or five students will put together several superobjectives over the period of each block). With that said, they tend to get a lot of information from research papers as well as UpToDate. I am not sure of the exact source used in this as the individual study guides will cite sources, but the superobjectives usually do not. However, I decided to clarify this for myself. A precursory look on UpToDate states that pulmonary edema is associated with surfactant deficiency (especially in RDS) due to the following: 1. Sodium channels that remove fluid tend to develop in a linear fashion with surfactant production (ie. preterm births tend to have both complications) 2. Inflammation due to lung injury 3. RDS patients tend to have low urinary output that exacerbates edema. "Pathophysiology and clinical manifestations of respiratory distress syndrome in the newborn" Firas Saker, MD A look through some of the study guides that mentioned similar phenomenon as I originally stated (in the first reply) cited a book that I do not have: Respiratory physiology-- the essentials (by John B. West). If I remember to do so, I will check for the book in the health science library and validate the source. Suffice it to say, I also like your posting on interstitial edema and it makes since. Thanks for the response! - on another note, in what situations would surfactant be deficient other than in RDS? If I remember correctly, it is related to NO somehow (foggy speculation)

You're most welcome. Always excited to hear from fellow educators!

Thank u .it is really supportive.

yousef Khozmi Firmly grasp it

Good ex planation

Thank you Dr Eric STRONG ,,,You are the best Doctor :)

Waiting to see quantum mechanics in medicine

@@harishguna4191 Here's a link to some videos from my buddies Corporis and Up and Atom who talk about quantum biology: kzfaq.info/get/bejne/kMlpi85qns2nomg.html

@@StrongMed thank you...ur lectures are helping me a lot

(Sorry for the delay in response - just saw your comment now!) Water molecules attract one another, and adhere to the inner surface of the alveolus. Think of it like this: As each water molecule attracts the molecules immediately adjacent to it, they get pulled together and the distance between them decreases. But if the distance between every possible pair of water molecules decreases, they must be moving closer to one another. As they are also attracted and adherent to the inner surface of the alveolus, this necessary must pull the alveolus inward. That is, until the inward pull of alveolus (quantified as the alveolar wall tension) is balanced by the air pressure inside.

darkenergylambda Thanks for the message. Unfortunately, I don't have any recommended resources for physics in medicine. It was that lack of resources that was one of my motivations for this specific topic as an entire video series.

+Beegslove Is it a matter of space optimization?

+Beegslove I would assume that's part of the explanation. Also, there is variability in the mechanical forces that act on different parts of the lung, which result in termporal and regional differences in alveolar size. As just one example, at night, when you are lying down on your back, your heart (which is an anterior structure) and which is relatively dense, compresses the lung tissue underneath it, resulting in something called atelectasis (mentioned in the video). Retrocardiac (i.e. behind the heart) atelectasis causes those alveoli to be underinflated relative to the alveoli in adjacent regions of the lung. Then during the day, when you are upright, that regional difference goes away.

It's not just the quantity of surfactant, but also the quality. In immature fetal lungs (

Thanks for the insight!

I had an original plan to follow this up with additional series in similar format: classic physical and chemistry topics (e.g. gases, optics, kinetics, etc...), broken down into short videos with a conventional textbook-like example, followed by a common medical application. But unfortunately, had too many competing requests from viewers and never got around to it. Hopefully someday...

Except the force is pulling to the *center of the alveoli*; not downward. I´ve read in a lot of medical books that the net force pulls downward, but its WRONG. This video explains it. That´s why alveoli collapse when there is no surfactant. Water molecules come very close together and that force that goes to the center of the alveoli makes it collapse!! I strongly recommend you to read the article cited in the description