Fluid Flow Resistance and Pressure in Human Physiology - Essay Example

The flow of blood in the circulatory system is directly related to the difference in pressure between the inlet and outlet of a vessel and is inversely related to the resistance to flow through that vessel. Resistance to flow through a vessel is also inversely related to its radius raised to the fourth power. Even a small decrease in the radius of the vessel would result in a large increase in the resistance to flow. At any given point in time, the most important factors governing the smooth functioning of the blood circulatory system are volume, pressure, resistance, and flow. For the optimal functioning of the system, it requires a specific pressure that is necessary and sufficient to ensure the flow of blood through all body tissues. The relation between pressure (P), resistance (R), and blood flow (F) is given by the equation, F = P/R. P precisely is the difference in pressure between the two ends of the system.

In systemic circulation, the flow of blood is determined by the cardiac output (CO) and PVR. PVR is obtained by rearranging the variables in the above-given equation as PVR = P/CO.

In pulmonary circulation, the total resistance is approximated at 0.12 PRU. In this case, the flow of blood is the same as systemic circulation. However, the pressure difference between the two ends of the system is much less. According to Poiseuilli, a French physician, the flow of blood is also affected by the viscosity of blood. It explains the resistance to flow due to the friction caused by the molecules present in the blood. Blood being a non-homogenous fluid, more molecules are present resulting in greater friction and hence increased resistance to flow.