venous pressure and pressure gradient

SamarEsawy

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    http://wiki.answers.com/Q/What_does_the_venous_return_depend_on

    Blood pressure at venous end of capillary: An increased pressure at the venule end of the capillary reduces venous return, because the pressure difference between the right atrium and the peripheral veins is reduced. Similarly a decrease in pressure at the venule end would increase venous return.

    http://www.askabiologist.org.uk/answers/viewtopic.php?id=1882

    Surely increasing the blood pressure in veins would help movement, and obviate the need for valves?

    No. Because the pressure gradient is reduced, there would be a problem with adequate circulation. In addition, the capillaries, where the business of gas and nutrient exchange takes place, have permeable walls. An increase in venous pressure would increase the pressure inside the capillaries leading to 'leak' of fluid from the blood into the tissue (a bit like tea being squeezed from a tea bag). The tissue becomes 'water-logged' (clinicians and scientists call this 'oedema') and it is a problem because it increases the distances that gases and nutrients must diffuse to meet the metabolic needs of the tissue. This problem happens in congestive heart failure, where the venous pressure increases due to inadequate pumping by the heart.

    how this happens I always think that increasing the blood pressure in veins would help movement
    thanks
     

    Jonari

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      You should post this in the USMLE Step 1 portion of the board. You'll get more responses there, and it'll help out other members who could potentially have the same question as you. :)
       
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      SamarEsawy

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        youre not increasing the pressure in the veins necessarily, you are doing it at the venule end of capillaries. if the difference between the arterial and venule end is small then flow will reduce through it.
        are you talking about filtration through the capillary?Do you mean that less fluid will be drained through veins on increasing pressure of venules so venous return will decrease?I don't understand
         

        Kaustikos

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          I still need help

          High venule pressure inhibits reabsorption and pretty much causes high filtration of fluids at the capillary (capillary leak). This decreases the fluid return at the venule end thus decreases the pressure in the veins. If you increase pressure at the venule you pretty much cause the capillaries to dumb all the hydrostatic pressure into the interstitium and cause leakage and edema. Low venule pressure causes reabsorption of fluid and brings the pressure up in the veins to allow venous return to be normal.

          Like this says - - You essentially get edema.

          The fluid that filters into the tissue flows within the intercellular space (the interstitium) and most of it is reabsorbed at the venular end of capillaries where the hydrostatic pressure is lower. Some of the filtered fluid is taken up by lymphatic vessels and returned to the circulation.

          Causes of Edema
          Edema may be caused by:

          Increased capillary hydrostatic pressure (as occurs when venous pressures become elevated by gravitational forces, volume expanded states, in heart failure or with venous obstruction)
          Decreased plasma oncotic pressure (as occurs with hypoproteinemia)
          Increased capillary permeability caused by proinflammatory mediators (e.g., histamine, bradykinin) or by damage to the structural integrity of capillaries so that they become more "leaky" (as occurs in tissue trauma, burns, and severe inflammation)
          Lymphatic obstruction (as occurs in filariasis)
           

          SamarEsawy

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            High venule pressure inhibits reabsorption and pretty much causes high filtration of fluids at the capillary (capillary leak). This decreases the fluid return at the venule end thus decreases the pressure in the veins. If you increase pressure at the venule you pretty much cause the capillaries to dumb all the hydrostatic pressure into the interstitium and cause leakage and edema. Low venule pressure causes reabsorption of fluid and brings the pressure up in the veins to allow venous return to be normal.
            That's awesome thank you for helping me I'm grateful :)
             

            Kaustikos

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              Well, now that we have an answer...

              tumblr_miegbto0lp1qemdrno1_500-fb95697f-original.gif


              go-fish-1-885cf165-sz550x341-animate.jpg

              medicina-a17b8266-sz640x682-animate.jpg

              tscodu1-c2633a30-sz420x294-animate.jpg


              And a reminder -

              2013-03-05-hadfield-c3562a50-sz850x5006-animate.jpg
               

              evilbooyaa

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                I would like the mods to come into this, the OP is constantly flooding the forum with questions he or she has. To the OP: you have professors....they are there to help!

                For what it's worth, this guy/gal is the only person asking questions from medical school on this forum. I like that these threads exist, since it's a good review of some pre-clinical aspects that I wouldn't really remember otherwise. I vote to let this person keep posting threads as people continue to explain the concepts. If people weren't answering his/her questions, then maybe my opinion would differ.
                 

                greatnt249

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                  For what it's worth, this guy/gal is the only person asking questions from medical school on this forum. I like that these threads exist, since it's a good review of some pre-clinical aspects that I wouldn't really remember otherwise. I vote to let this person keep posting threads as people continue to explain the concepts. If people weren't answering his/her questions, then maybe my opinion would differ.

                  I agree in principle, but there IS a sub-forum dedicated to this kind of thing, namely, the Step I/II area.
                   

                  SamarEsawy

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                    For what it's worth, this guy/gal is the only person asking questions from medical school on this forum. I like that these threads exist, since it's a good review of some pre-clinical aspects that I wouldn't really remember otherwise. I vote to let this person keep posting threads as people continue to explain the concepts. If people weren't answering his/her questions, then maybe my opinion would differ.

                    You guys realize that no one is forcing you to read these threads, right?

                    yes. plus she's kinda funny. like how she keeps asking over and over. it's cute.
                    thank you all for encouraging me to ask :)
                    some people here keep depressing me all the time instead of answering my questions or at least benefit from them so yeah thank you so much
                     

                    Kaustikos

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                      thank you all for encouraging me to ask :)
                      some people here keep depressing me all the time instead of answering my questions or at least benefit from them so yeah thank you so much

                      If it's worth anything - the BRS physiology has an excellent overview of all this stuff. I'd recommend picking that up :)
                       
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