Let's say inflammation occurs. The capillaries dilate. WBC are released from the capillaries and fluid. Hypotension occurs. Is this because the volume of fluid is lost to the interstitium, or, is this because of the dilation? Both of these might contribute to hypotension, I think.
Understanding Blood Flow Properties
- Thread starter RH8448
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Both the lower blood volume due to fluid loss and vasodilation contribute to hypotension in this case. However, you can get hypotension without vasodilation by dehydration and excessive fluid loss due to illness etc.
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Just keep in mind that most vasodilation is pretty location-specific. Some of these responses almost make it sound like large portions of the cardiovascular system are dilating/constricting. Usually it is specific to arteries or arterioles leading up to a specific capillary bed or organ, allowing for very specific "shunting" of blood from one place to another. So, when talking blood flow and pressure, I doubt systemically a swollen goose egg on your head is going to effect flow rate in your leg.
Just think of a local portion of a vessel like its own little container/pipe/spigot system. Its going to follow all the same fluid physics rules. If container volume is constant and fluid volume increases you're going to get more pressure, if you take out fluid without changing container volume you are going to get less pressure; pressure differentials are what cause the flow, and the flow rate is dependent on the diameter of the vessel (cross-sectional area specifically); the system changes like any fluid flowing through a more or less constricted region. Don't forget that actual blood vessels are going to be non-ideal flow, so its moving fastest in the center and slower near the sides. Definitely understand the continuity equation: Q = AV. Truly understanding those basics should make you golden for MCAT-2015.
Just think of a local portion of a vessel like its own little container/pipe/spigot system. Its going to follow all the same fluid physics rules. If container volume is constant and fluid volume increases you're going to get more pressure, if you take out fluid without changing container volume you are going to get less pressure; pressure differentials are what cause the flow, and the flow rate is dependent on the diameter of the vessel (cross-sectional area specifically); the system changes like any fluid flowing through a more or less constricted region. Don't forget that actual blood vessels are going to be non-ideal flow, so its moving fastest in the center and slower near the sides. Definitely understand the continuity equation: Q = AV. Truly understanding those basics should make you golden for MCAT-2015.
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