[Catalist] Physiol question

[Stephen Treloar]

Hi all
In the Y12 STAWA manual (Ex 4 Q11) there is a question about the influence of temperature drop on Urine output.
After a bit of thought, not helped by Googling (to cover this specific question) but Googling DID help to come up with the answer below (which conflicts with the STAWA model answer).

11.      "In cold weather blood vessels in the skin constrict causing blood to move into the body core circulation. This increases blood pressure" (maybe...maybe not, as the skin blood vessel constriction is matched by internal organ vessel dilation is it not? - it has to go SOMEWHERE! So the blood pressure may indeed NOT rise for starters?).
"Indicate with up or down arrows what would happen in the following feedback loop".
Answer shows BP rising, ADH falling hence Urine increase and blood volume decrease.
My issues with this:
i) Data from osmoreceptors, also going to the hypothalamus, would indicate normal osmolarity (as it was)...so, with the Hypothalamus being a good little modulator ADH would stay the same (?) as losing water here would then unbalance the osmolarity (Just to fix BP) and that's not smart (as a response to cold)? OR
ii) Maybe ADH would even rise (?) to assist in reabsorption of the extra filtrate caused by the higher blood pressure.
iii) The feedback loop starts with a stimulus of "BP increase", and response of "blood volume decrease". If nothing else, this is not the correct way to express the response as the feedback is to the stimulus, so the "response" should be "decreased blood pressure".


While the simple thing would be to just do as the question directs, I struggle with this when the content/science is perhaps flawed (or I coooooulld be wrong). Either way, it made a good discussion and the kids agreed with my logic/the intellectual exercise - applying what they have learned.
I'm wondering if this question was created to link to how we urinate more frequently in cold weather?, which I believe is more due to the fact that we lose less water through evaporation (while still having similar inputs), so osmolarity decreases, and so ADH does....and so it goes (due to osmolarity changes, not BP changes).
Anyone with some Physiol background want to weigh in?

Steve Treloar



Stephen Treloar
Head of Senior School

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