Biology - Relative Pressures Question

[sciencebooks]

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Hey everyone, a quick question on the difference between things affecting osmotic and hydrostatic pressure.

So the question ends: "Reducing the amount of albumin to below-normal levels would most likely have which of the following effects?"

I understand that this would decrease the osmotic pressure of the blood and thus increase the relative osmotic pressure of the surrounding tissues as the explanation describes. However, why would the loss of protein from the plasma NOT affect the hydrostatic pressure? For example, I thought that adding ions increased blood pressure? Wouldn't taking "things" out similarly decrease it?

 

[Jepstein30]

Hey everyone, a quick question on the difference between things affecting osmotic and hydrostatic pressure.

So the question ends: "Reducing the amount of albumin to below-normal levels would most likely have which of the following effects?"

I understand that this would decrease the osmotic pressure of the blood and thus increase the relative osmotic pressure of the surrounding tissues as the explanation describes. However, why would the loss of protein from the plasma NOT affect the hydrostatic pressure? For example, I thought that adding ions increased blood pressure? Wouldn't taking "things" out similarly decrease it?

No, because if you take ions OUT of plasma, you'll have a net flow of water OUT of the vein/artery.. leading to a decreased blood pressure.

When you add stuff to blood, you'll get water flowing into the blood to dilute it.. leading to more volume and therefore a higher blood pressure.

 

[sciencebooks]

No, because if you take ions OUT of plasma, you'll have a net flow of water OUT of the vein/artery.. leading to a decreased blood pressure.

When you add stuff to blood, you'll get water flowing into the blood to dilute it.. leading to more volume and therefore a higher blood pressure.

Yeah, that's what I was saying above. (If things are taken out, I thought there would also be a decrease in BP.) However, the answer description flat out said "It would not affect the hydrostatic pressure (blood pressure, choices B and C and wrong)." I was just confused as to why it claims it would NOT be affected? Maybe it was suggesting that removal would cause the immediate difference in osmotic pressures that causes the flow and that the change in hydrostatic pressure would only be as a result of that?

 

[Jepstein30]

Yeah, that's what I was saying above. (If things are taken out, I thought there would also be a decrease in BP.) However, the answer description flat out said "It would not affect the hydrostatic pressure (blood pressure, choices B and C and wrong)." I was just confused as to why it claims it would NOT be affected? Maybe it was suggesting that removal would cause the immediate difference in osmotic pressures that causes the flow and that the change in hydrostatic pressure would only be as a result of that?

Where was this question?

Could be missing something in the stem itself?

 

[sciencebooks]

Where was this question?

Could be missing something in the stem itself?

Here is is. (Thank you, by the way!)

Question:

Large proteins, most notably albumin, are dissolved in the plasma and serve an important role in regulation of plasma volume. Reducing the amount of albumin to below-normal levels would most likely have which of the following effects?

Answer:

Movement of water from the bloodstream into the tissues with resulting swelling, due to reduced osmotic pressure

Explanation:

D. The loss of protein from the plasma would cause the osmotic pressure of the blood to go down (choice A is wrong). It would not affect the hydrostatic pressure (blood pressure, choices B and C and wrong). The reduced osmotic pressure of the blood will have the effect of allowing water to leave the bloodstream and enter the tissues, where it will cause the tissues to swell. (You can also think of it as the tissues’ relative osmotic pressure increasing, thus they have a greater tendency to draw water out of the blood.)

Lol, like I said, I completely get the answer, but I have this habit of going through every question's answer description even when I get them right and then sometimes get tripped up on their explanations.

 

[Jepstein30]

Here is is. (Thank you, by the way!)

Question:


Answer:


Explanation:


Lol, like I said, I completely get the answer, but I have this habit of going through every question's answer description even when I get them right and then sometimes get tripped up on their explanations.

Yea no clue there. Would think it would have an indirect effect on hydrostatic pressure by reducing the osmotic pressure... but don't know.

TBR?

 

[sciencebooks]

Yea no clue there. Would think it would have an indirect effect on hydrostatic pressure by reducing the osmotic pressure... but don't know.

TBR?

Yeah, I still kind of think so. Haha, no, TPR additional online content. Thanks for your help though, 🙂.

 

[ThirdEye]

For purposes of the MCAT, hydrostatic pressure is independent of albumin because 100ml of blood has the same hydrostatic pressure regardless of the concentration of albumin.

But you are correct. There is an indirect effect because as albumin drops, blood volume drops a little.

 

[member232]

Also, hydrostatic pressure is generated by the force of the heart. Changes mainly depend upon drops in pressure due to going from arteries to arterioles to capillaries to venules to veins. Osmotic pressure is the one that is constant due to albumin levels. Thus, when you reduce albumin, the osmotic pressure that normally pulls fluid in (opposing hydrostatic force that pushes fluid from the circulatory system to tissues) is decreased. However, hydrostatic force is relatively constant, since the heart force is unaffected. There will be a relative net force out of the circulatory system into the tissues.

hope that helps!

 

[sciencebooks]

For purposes of the MCAT, hydrostatic pressure is independent of albumin because 100ml of blood has the same hydrostatic pressure regardless of the concentration of albumin.

But you are correct. There is an indirect effect because as albumin drops, blood volume drops a little.

Oh, okay, I didn't know this so thank you! Is it just albumin or do proteins typically not affect hydrostatic pressure?

Also, hydrostatic pressure is generated by the force of the heart. Changes mainly depend upon drops in pressure due to going from arteries to arterioles to capillaries to venules to veins. Osmotic pressure is the one that is constant due to albumin levels. Thus, when you reduce albumin, the osmotic pressure that normally pulls fluid in (opposing hydrostatic force that pushes fluid from the circulatory system to tissues) is decreased. However, hydrostatic force is relatively constant, since the heart force is unaffected. There will be a relative net force out of the circulatory system into the tissues.

hope that helps!

Thanks. I understand that hydrostatic pressure (for example, blood pressure) is dependent on the force and I'll think of it more in terms of this now instead of over-thinking how they'd all be indirectly affected, lol. However, we do learn that things like ions increase blood pressure. For example, aldosterone increase Na+ reabsorption and thus increases blood pressure. Is this one of the few times I should think of hydrostatic pressure as well? (Obviously, osmotic pressure also increases).

 

[ThirdEye]

Oh, okay, I didn't know this so thank you! Is it just albumin or do proteins typically not affect hydrostatic pressure? [........aldosterone increase Na+ reabsorption and thus increases blood pressure. Is this one of the few times I should think of hydrostatic pressure as well? (Obviously, osmotic pressure also increases).

It's probably best that you only consider hydrostatic pressure to change only if blood pressure and resistance change. Lots of things alter blood pressure, and Na/h2o reabsorption will increase blood pressure indirectly leading to increased H.P. However, if you're ever asked "which solutes alter HP?", the answer is none. The MCAT won't likely trick you with things like this

 

[sciencebooks]

It's probably best that you only consider hydrostatic pressure to change only if blood pressure and resistance change. Lots of things alter blood pressure, and Na/h2o reabsorption will increase blood pressure indirectly leading to increased H.P. However, if you're ever asked "which solutes alter HP?", the answer is none. The MCAT won't likely trick you with things like this

Okay, thank you. BP and resistance ---> hydrostatic pressure. Ions and other solutes ---> osmotic pressure.