Looked it up and found that because you’re in a supine position for a long time you’re going to have increased venous return which leads to increased CO. This negatively feedsback on RAAS, leading to decreased aldosterone. As a result, you’re going to have increased diuresis which leads to decreased blood and plasma volume.
Why is the answer decreased blood volume as opposed to decreased plasma sodium concentration?
I use parasympathetic/ sympathetic principles to figure this out. If you're laying down, you're most likely resting and digesting. That rules out E, C (RAAS is due to high Sympathetic tone) and also D (high plasma volume is a result of RAAS). This left A and B. Decreased plasma sodium volume would have been the case if he was drinking a lot of water, or had SIADH possibly. I couldn't really find the connection between this option and his PNS activity. So I went for A, especially because it was directly opposite of one option I KNEW was wrong.
Found this link pretty helpful: https://www.nursingtimes.net/clinical-archive/cardiovascular/effects-of-bedrest-1-cardiovascular-respiratory-and-haematological-systems/5002005.article
FROM THE ANSWER CHOICES, ITS A RENAL POHYSIOLOGY QUESTION, SO THE GUY THAT MENTIONED ABOUT THE ANP STUFF MAKES THE MOST SENSE.
GRACIAS TEASCATSBISCUITS
submitted by ∗tea-cats-biscuits(273)
Because you are supine, there’s increased preload going back to your heart (no need to work against gravity, your blood isn’t pooling in your legs as much either). As a result, ANP is secreted due to RA stretch, leading to diuresis and a reduction of blood volume.