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SB B/B Q4 and 7
Posted: Sun Aug 11, 2019 7:43 pm
Q4 when I think of SNS I think of vasodilation but the passage states "[vessels] can dilate or further constrict to alter blood flow" but I'm not sure why the answer is "moderates blood flow"
Q7 How do you narrow down B and C (A and D eliminated because Gpcr43–/– mice gain weight)
Re: SB B/B Q4 and 7
Posted: Wed Aug 21, 2019 1:03 am
Hey there! I didn't mean to drop this by the wayside for a week, my bad!
The effects of the SNS will be varied depending on location. What is body-wide however is an increase in heart rate, since the heart will be beating faster and harder (chronotropic and inotropic effects of epinephrine & norepinephrine). The brain itself wants a very constant chemical environment, and a drastic increase in blood pressure would a) possibly endanger some arterioles and b) definitely lead to an increase in hydrostatic pressure in the capillaries, forcing fluid out of them and across the BBB. Since our brain is fairly sensitive, we probably don't want to be changing the amount of fluid sloshing around there drastically anytime - we would rather keep internal cerebral pressure as constant as possible.
The passage describes one major way that this happens: The myogenic response, a way in which the vessels themselves regulate pressure locally. Namely, they can constrict during high systemic pressure and therefore prevent a buildup of pressure in the brain. Neat!
B is saying that being germ free led to WT gaining weight the same way Gpcr43 knockouts did - meaning that without a microbiome, they could not produce SCFAs and therefore there was no ligand activating GPCR43 signaling in adipose tissue. And in the Gpcr43 knockouts, it is suggesting that GPCR signaling was not activated whether a microbiome was present or not (which makes sense, since the receptor should be absent!).
C on the other hand is saying that it made no difference whether WT mice were germ-free or not. Which would suggest that at least GPCR43 wasn't a very significant source of metabolic signaling - which is inconsistent with what the background from the passage tells us.