human physiology thoughts...

[scottyhoop]

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Working on a human phys problem...here it is. My abbreviated answers are in (). Am I on the right track with this? Thanks!!

Jane and Carla are both running the Boston Marathon. They are 25 years old and have equivalent training regimens and marathon experience. Water and electrolyte-containing sports drinks are available at stations located at each milepost during the race.
Data similar for both women:
Pre-race weight: 60 kg (132 lbs)
Avg sweating rate (for race conditions): 1 L/hr
Pace: 8 min/mile

After completing 5 miles
A. Carla has ingested a relatively small amount of water (≈ 250 ml) from the aid stations.
For each of the following variables indicate, at this point in the race, whether the variable will be increased, decreased or unchanged compared to Carla’s resting values. Explain, incorporating into your explanation cardiovascular (CV), renal and any other system responses that are appropriate and relevant.

1. Heart Rate-(Heart rate will be increased due to the need of increased O2 delivery to body tissues due to exercise)
2. Blood Pressure-(Blood pressure will be increased due to a combination of increased heart rate and loss of water)
3. ADH (AVP) [Antidiuretic Hormone (arginine vasopressin)]-(Levels will be increased due to increased needs for water reabsorption.)
4. Angiotensin II-(increased levels due to increased need for Na reabsorption-triggers release of aldosterone)
5. Aldosterone-(increased levels since triggered from increased angiotensin I activation into angiotensin II)

 

[armorshell]

Seems OK, note that water loss, in isolation, is actually going to lead to a decrease in blood pressure (Which is why a lot of people take things like HCT). In this case her BP should still be increased due to the increased cadiac output.

 

[scottyhoop]

Seems OK, note that water loss, in isolation, is actually going to lead to a decrease in blood pressure (Which is why a lot of people take things like HCT). In this case her BP should still be increased due to the increased cadiac output.

Good call on the water loss...my bad. So you agree that cardiac increase will beat out the effects of water loss in this scenario? Thanks for the input!!

 

[Streetwolf]

Good call on the water loss...my bad. So you agree that cardiac increase will beat out the effects of water loss in this scenario? Thanks for the input!!

Absolutely. You got other things helping out too (to some degree). Cortisol levels will be up which will bump up BP. You already mentioned a faster heart beat because more O2 is required. You'll have more sympathetic output which serves to increase contractility of the heart (as well as increase HR). Muscle contraction (esp in the legs) will help bring blood back into the RA which increases preload, leading to a larger SV which increases CO.

Water loss on its own leads to a decreased SV which means a lower CO and BP. Over time the water loss will predominate over the other factors, but this early in the race I'd say she's still good to go. But she better get some more into her ASAP.

 

[rollypolly]

Blood pressure decreases with dehydration because of a loss of blood volume. The question is kind of tricky because she really isn't that far into her marathon and so she isn't that dehydrated in marathon terms. Either way, if you answer that her blood pressure increases for #2 then you should rethink your answers to #4 and #5. When blood pressure decreases, the juxtaglomerular cells in the kidney secrete renin, which ultimately results in angiotensin II and aldosterone. Angiotensin II works to increase blood pressure and to secrete aldosterone, which increases the reabsorption of sodium in the kidneys. So, if blood pressure were to increase, the renin-angiotensin-aldosterone would not be activated, and so there would not be increased levels of angiotensin and aldosterone.

My thinking is that your #1 and #3 are spot on. I think #2 should be that her BP is decreased because of a loss of blood volume resulting from sweat that she has not fully compensated for. Then, if you put decrease in BP for #2 then your answers for #4 and #5 are correct.

😀

 

[AlcoHulk]

Good stuff. Also, Angiotensin II would increase peripheral resistance (powerful vasoconstrictor) to increase BP due to lower ECF volume (blood volume).