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Ex-USMLE Forums Staff
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Discussion Starter · #1 ·
Weightless environment is frequently tested concept in physiology questions in USMLE Step 1.
Here's a short encounter

The starting point in the way that we should think of this is that weightlessness will redistribute the venous blood that is normally pooled in the gravity dependent veins to other areas of the body including the large veins and the right side of the heart, this will cause the following

  • Baroreceptor stretch and so more signals and so decreased sympathetic tone, the latter will cause less Juxtaglomerular apparatus stimulation and so less renin and so less Na retention.
  • The same baroreceptor stretch will cause less ADH secretion which again contributes to water excretion and contracted ECF.
  • The loss of gravity will remove the normal inhibition of decalcification and you end up losing Calcium.
 

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Ex-USMLE Forums Staff
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753 Posts
Discussion Starter · #3 ·
It's not known

the one thing i dont get is the loss of Ca, cld you pls explain?
When you remove stress on the bones they stop producing ostoeblasts and gradually you develop osteoporosis.
It has been documented that some NASA astronauts have lost up to 20% of their bone mass in as little as six months zero gravity.
How exactly that happens is still under research. One of the theories involve creatine kinase B.
Breakthrough therapy with glucose-dependent insulinotropic peptide is promising some hope to prevent this.
For further reading please refer to this page
http://science.nasa.gov/science-news/science-at-nasa/2001/ast01oct_1/
 
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