midterm bio question

[Dentalicous1234]

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#13: a capillary has : higher hydrostatic pressue at arteriole end and lower hydrostatic pressue at the venule end

How is this true? This made me think of physics when the cross sectional area decreases the speed of the liquid increases so I thought the pressue would increase as well in the capillary as compared to the arteriole since the cappillary is smaller? Am I thinking too much in this or am I remembering my physics wrong?

 

[zackscoot]

#13: a capillary has : higher hydrostatic pressue at arteriole end and lower hydrostatic pressue at the venule end

How is this true? This made me think of physics when the cross sectional area decreases the speed of the liquid increases so I thought the pressue would increase as well in the capillary as compared to the arteriole since the cappillary is smaller? Am I thinking too much in this or am I remembering my physics wrong?

the hydrostatic pressure is the result from the pumping action of the heart. As you go from the arteriole --> capillary --> venules, you lose pressure from increase in cross total cross sectional area of capillary. You have to take into consideration of the TOTAL CROSS sectiona area of ALL capillaries. which is much greater than the total cross sectional area of arterioles. This result in slowing down of the blood so that better exchange can occur and prevent high pressure from busting the capillary open since they are only 1 cell thick.

Furthermore, as blood move from arteriole to venule end, friction/peripheral resistance decrease the pressure drastically. and that's actually the main reason why the hydrostatic pressure is so low at the venule end.

 

[Dentalicous1234]

okay that def. makes sense but was my physics reasoning wrong? as cross sectional area increases pressure and speed decrease. I think it's still right but like you said I wasn't considering the TOTAL area of all the capillaries which is much greater than the arteriole so increased area = lower pressure and speed...right?

also, I was reading another question and it said that estrogen is also responsbile for maintaining the copus leutem. I looked it up and it does do that but I always attribute progestrone for this function. So if we get a question that askes what maintains the corpus leutum and it has estrogen and progesterone...what do we pick? progesterone?

 

[Flipper405]

okay that def. makes sense but was my physics reasoning wrong? as cross sectional area increases pressure and speed decrease. I think it's still right but like you said I wasn't considering the TOTAL area of all the capillaries which is much greater than the arteriole so increased area = lower pressure and speed...right?

also, I was reading another question and it said that estrogen is also responsbile for maintaining the copus leutem. I looked it up and it does do that but I always attribute progestrone for this function. So if we get a question that askes what maintains the corpus leutum and it has estrogen and progesterone...what do we pick? progesterone?

I am currently doing the circulatory system in my Bio class, and we talked about this today... the physics reasoning is semi-right. Like the last poster said, you have to consider the total area of the all the capillaries. The total cross-sectional area in the capillaries is MUCH bigger to allow for exchange with the interstitial fluid. anyway, got an ochem test in about 20 minutes so i gotta go...

and i have no idea about the estrogen question

 

[Prometheous19]

progesterone is produced by the corpus luteum and prevents menstruation from occuring.

 

[Dentalicous1234]

right so it helps maintain the corpus leutum...but so does estrogen. So what would be the right answer...they both help maintain it so how would you pick one if asked about that function? or would they just not ever ask for one then since 2 hormones are responsible?

 

[phraud]

#13: a capillary has : higher hydrostatic pressue at arteriole end and lower hydrostatic pressue at the venule end

How is this true? This made me think of physics when the cross sectional area decreases the speed of the liquid increases so I thought the pressue would increase as well in the capillary as compared to the arteriole since the cappillary is smaller? Am I thinking too much in this or am I remembering my physics wrong?

I think you're misreading the question. It's not asking you to compare capillary pressure and arteriole pressure, it's asking you to compare pressure at the arteriole end of the capillary to the pressure at the venule end of the capillary.

I could be wrong though...

The pressure drop is due to the lost of blood plasma to the lymphatic system, which is usually about 10% (I think).

 

[Dentalicous1234]

okay this makes sense too. Comparing the ends didn't phase me at first because shouldn't they be the same size? I guess I forgot to take into account that at the venule end there is less stuff in the cappillary (like you explained because blood plasma amount decreases) and so that's what will make the artery end have more pressue since theres more stuff present there.

thank you!🙂

 

[zackscoot]

also, I was reading another question and it said that estrogen is also responsbile for maintaining the copus leutem. I looked it up and it does do that but I always attribute progestrone for this function. So if we get a question that askes what maintains the corpus leutum and it has estrogen and progesterone...what do we pick? progesterone?

I think you got it wrong here. Estrogen is not responsible for maintaining the corpus luteum. What's helping maintaining it is the amount of LH present in the body. Estrogen and progesterone is secreted by the corpus luteum. which together inhibit (negative feedback) the release of LH. Without LH for a long time, corpus luteum atrophy, and thus decrease estrogen and progesterone secretion. and increase LH secretion which led to a new cycle.

When pregnancy occurs, hCG or hGC (can't remember) which is secreted by the fertilized egg, will mimic the effect of LH and thus maintain corpus luteum and prevent atrophy. After development of placenta, the placenta will continue secrete progesterone and estrogen and replace the function of corpus luteum and decrease LH level and prevent new cycle.

THE MAIN FUNCTION OF ESTROGEN AND PROGESTERONE IS TO MAINTAIN THE ENDOMETRIAL WALL AND PREPARE IT FOR IMPLANTATION!!! THEY ARE NOT USED TO MAINTAIN CORPUS LUTEUM. THEY ARE SECRETED BY CORPUS LUTEUM!!!

 

[zackscoot]

okay this makes sense too. Comparing the ends didn't phase me at first because shouldn't they be the same size? I guess I forgot to take into account that at the venule end there is less stuff in the cappillary (like you explained because blood plasma amount decreases) and so that's what will make the artery end have more pressue since theres more stuff present there.

thank you!🙂

I don't think u got the concept right. Hydrostatic pressure is the pressure from the heart. oncotic pressure is the osmotic pressure in the blood.

The reason water/nutrients are pushed out from the arteriole end is because there is a higher hydrostatic pressure at that particular end. This is due to the pumping action of the heart. and as u move from the arteriole to the venule end, you are expriencing peripheral resistance (like friction) and as the result, you are losing pressure from this. However, since water are leaving, the filtrate concentration (salt, protein etc) will increase inside of the blood vessel. This will increase the oncotic pressure at the venule end which will draw the fluid back into the vessel at the venule end (while the amount of fluid is less, this is not the cause of a drop in HYDROSTATIC PRESSURE. Like i said before hydrostatic pressure is the pressure from the pumping action of the heart.

In conclusion, the main reason why there is a drop in BP is due to the peripheral resistance/friction with the vessel wall as u moved from the arteriole to venule