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    Hemodynamics (Blood flow, Pressure and Resistance)

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    Please help me with these. I am looking for not a very long answers to help me understand this topic better
    1. What structural features of arteries and veins lead to an equilibrium in blood flow into and out of any given organ? Consider the relationship of flow to pressure and resistance in your answer (F=P/R).
    2. Explain what is different and/or similar between the autonomic regulation of cardiac output and blood pressure.

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    Solution Preview

    In the following paragraphs I have explained the concepts of hemodynamics. Fishing-out the answer you require won't be difficult once you grasp the concepts. Also please refer to the attached PowerPoint Slides as referred in the material below.

    First let me explain the equilibrium in blood flow. To understand the concept off equilibrium and how the structural features of arteries and veins affect that equilibrium we have to first understand the term cardiac output (CO), which means the rate of blood flow out of the heart (expressed in L/min). The heart is the central driver of the circulatory system and by the actions of constant contraction and relaxation the heart pumps blood throughout the whole body. Oxygenated blood from the heart first goes into the aorta, which is the largest artery of the body. Blood then goes into smaller and even smaller arterioles and then finally enters the capillaries. This is the region of micro-circulation. At the location of microcirculation oxygen, glucose and various enzyme substrates exchange with cells of the body take place. Capillaries pass blood to venules. Venules carry de-oxygenated blood to the right side of the heart from where it enters the lungs to get oxygenated again and to be circulated back to the body via the aorta (PowerPoint Slide #1).
    A state of equilibrium is always maintained in normal circulation where the volume of oxygenated blood that is pumped out of the heart every minute (cardiac output) via aorta approximately equals to the volume of de-oxygenated blood that is returned back each minute via the veins to the heart. Since this equilibrium is maintained at every level of the circulatory system the velocity of blood flow at each level is determined by the cross-sectional area of that particular level and this is expressed by a simple mathematical equation (PowerPoint Slide #2):

    v = Q/A
    v = velocity (cm/s)
    Q = blood flow (ml/s)
    A = cross sectional area (cm2)

    Hagen-Poiseuille equation:
    It is important to understand the Hagen-Poiseuille equation to understand vascular resistance, which means the force, required to move the blood across the circulatory system. Lets say you want to blow air through a cardboard tube (e.g. Kitchen Paper Roll). Lets say the length of the kitchen paper roll is "L" and the radius is "R" and lets imagine the kitchen paper roll is about 2 cm in radius. You realize that it is easy to take one breadth of air and blow into this roll. So you now ...

    Solution Summary

    The material here explains the various concepts of Hemodynamics explaining the relationship among Blood flow (cardiac output), arterial pressure and resistance. Also is explained the mechanisms by which the autonomous system regulates blood pressure in situations when there is a fall in blood pressue.