AAMC 9 BS Q's # 166, 168

[bambina01]

Could someone PLEASE explain this to me. I got both of these questions wrong on AAMC 9 and in looking back at them, they both have to do with "interstitial fluid" something I am confused about.

Please bear with me, I am a mature student, and not a bio major so I have had to learn everything on my own.

For Q 166, "Albumin is the manjor blood osmoregulatory protein. The most likely effect of a sharp rise in the level of serum albumin is" :

the answer was D- An influx of interstitial fluid into the bloodstream.

For Q 168 " Capillaries in the kidney and elsewhere in the bdy maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following isthe initial effect of a blood clot forming on the venous side of a capillary bed?

the answer was A-Net fluid flow in the direction of interstitial fluid.

I have the AAMC soln, but I am missing the main idea behind interstitial fluid, I looked it up in TPR and EK, but could not find an explanation.

Help Please! 😱

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[Mr. Tee]

166. This question is asking for the EFFECT of a rise in albumin; reword the question to read "what happens after you increase albumin concentration in the blood?" If you increase the solute concentration of the blood, water is going to enter the bloodstream by osmosis. Choice D is the only one that fits this.

168. The osmotic pressure throughout the capillary pushes fluid back into the bloodstream, and this pressure is constant. The hydrostatic pressure from the blood wants to force fluid out of the bloodstream, so this opposes the osmotic pressure. The hydrostatic pressure is greater than the osmotic pressure at the arterial end of the capillary (net fluid flow out of the capillary) and less than the osmotic pressure at the venous end of the capillary (net fluid flow into the capillary).

Reworded, the question reads "What happens when fluid can't flow into the venous end?" This means that the hydrostatic pressure will build up in the capillary since fluid can't leave. The fluid is effectively shunted toward leaving the capillary into the interstitial fluid (this is the only path it can take, because fluid can either enter the interstitial fluid or the veins). This will occur since the hydrostatic pressure increases, forcing net flow of fluid out of the capillary.

Another way to tackle this question is through the process of elimination. You can cross out C and D since the osmotic pressure will stay the same. Since hydrostatic pressure increases, net fluid flow into the interstitial fluid cannot decrease.

 

[Sol Rosenberg]

Could someone PLEASE explain this to me. I got both of these questions wrong on AAMC 9 and in looking back at them, they both have to do with "interstitial fluid" something I am confused about.

Please bear with me, I am a mature student, and not a bio major so I have had to learn everything on my own.

For Q 166, "Albumin is the manjor blood osmoregulatory protein. The most likely effect of a sharp rise in the level of serum albumin is" :

the answer was D- An influx of interstitial fluid into the bloodstream.

For Q 168 " Capillaries in the kidney and elsewhere in the bdy maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following isthe initial effect of a blood clot forming on the venous side of a capillary bed?

the answer was A-Net fluid flow in the direction of interstitial fluid.

I have the AAMC soln, but I am missing the main idea behind interstitial fluid, I looked it up in TPR and EK, but could not find an explanation.

Help Please! 😱

#166

An increase in albumin (a plasma protein) would increase the osmolarity of the plasma. Water flows from regions of low to high osmolarity, so there would be a net flow of water INTO the plasma from the interstitial fluid. The interstitial fluid is just the fluid surrounding cells in tissues.

#168

First, re-read the question. The net flow into/out of capillarities is determined by the hydrostatic and osmotic pressures. Hydrostatic pressure at the arteriolar side of the capillaries drives fluid (and solutes) out of the plasma and into the tissues (interstitial fluid) whereas osmotic pressure at the venule side of the capillaries is what is responsible for resorbtion of waste products, etc. (#166 above dealt with osmotic pressure gradient changes.) This question deals with hydrostatic pressure changes. Blocking the capillary at the venule side will cause hydrostatic pressure to increase. There will be no change in osmotic pressure. Therefore, if hydrostatic pressure increases relative to osmotic pressure, there will be greater net efflux of fluid from the plasma to the tissues (interstitial fluid.)

 

[bambina01]

Thank you Teerawit and jota_jota for those excellent explanations!

They make sense to me, I think the only thing that still confuses me is if interstitial fluid is the fluid surrounding the cells, where does the blood come into that? i.e. I thought it was the cell, and then you have blood surrounding the cells, where is the blood in relation to the interstitial fluid? 😕

 

[Mr. Tee]

Thank you Teerawit and jota_jota for those excellent explanations!

They make sense to me, I think the only thing that still confuses me is if interstitial fluid is the fluid surrounding the cells, where does the blood come into that? i.e. I thought it was the cell, and then you have blood surrounding the cells, where is the blood in relation to the interstitial fluid? 😕

The blood doesn't "surround" the cells but rather stays in the blood vessels. The interstitial fluid bathes the cells and the cells get nourishment from this fluid. Nutrients from the blood can leave the blood vessels via capillaries and into the interstitial fluid, for reception by the cells.

 

[bambina01]

The blood doesn't "surround" the cells but rather stays in the blood vessels. The interstitial fluid bathes the cells and the cells get nourishment from this fluid. Nutrients from the blood can leave the blood vessels via capillaries and into the interstitial fluid, for reception by the cells.

whoops,

 

[bambina01]

The blood doesn't "surround" the cells but rather stays in the blood vessels. The interstitial fluid bathes the cells and the cells get nourishment from this fluid. Nutrients from the blood can leave the blood vessels via capillaries and into the interstitial fluid, for reception by the cells.

okay, that makes sense to me.

thanks Teerawit, you-da-bomb! 😉

Good Luck on Saturday

 

[albaniandoc]

I missed the second one. MY reasoning was that since there is no way to drain the venous side, the interstitial fluid will back up (kind like a toilet). Once the pressure in the interstitium is increased from increased fluid retention it would decrease the flow out of the capillary since the capilary will have to pump against a higher pressure than before. But I see how my reasoning was wrong. I imagine that eventually this would happen.

 

[albaniandoc]

posted twice

 

[Mr. Tee]

Good Luck on Saturday

You too!