The flow rate (F) of blood through a blood vessel describes the volume of blood
ID: 3518011 • Letter: T
Question
The flow rate (F) of blood through a blood vessel describes the volume of blood that passes through the vessel per a unit of time. Flow rate is affected by physical variables like the resistance of the blood vessel (R) and the pressure gradient within the blood pressure.
1). Which one of the following statements correctly summarizes the relationships between these variables?
(A) Flow rate is directly proportional to the pressure gradient and inversely proportional to the resistance.
(B) Flow rate is directly proportional to the resistance and indirectly proportional to the pressure gradient.
(C) Flow rate is equivalent to the pressure gradient multiplied by the resistance.
(D) Flow rate is equivalent to the pressure gradient minus the resistance.
Since blood flows from areas of high pressure to areas of low pressure, blood pressure is higher at the start of a vessel and lower at the end. The pressure gradient (P) is the difference in pressure between the beginning and the end of a given length of blood vessel.
Consider the relationship between pressure gradient and flow rate and examine the following images. Each image compares two segments of blood vessel of equal length and radius and identifies the pressure at the beginning and end of each vessel. For each pair of vessels, determine which (if either) has the higher flow rate.
2). Along with pressure gradient, the other major variable that affects flow rate is the resistance (R) of the blood vessel. Resistance is affected by the viscosity (thickness, n) of the blood, the length of the blood vessel (L), and the radius (r) of the blood vessel. Complete the following chart to indicate how changes in these variables tend to affect resistance. (For each change, assume that all other variables stay the same.)
3). Of these three variables, which one is the most important in determining resistance (R)?
a) vessel radius
b) blood viscosity
c) vessel length
An increase in blood viscosity (n) tends to ________ resistance (R). Increase or decrease An increase in vessel length (L), tends to _________ resistance (R). Increase or decrease An increase in vessel radius (r) tends to __________ resistance (R). Increase or decrease 65 mm Hg 40 mm Hg 40 mm Hg 10 mm Hg Vessel A Vessel A Vessel B Vessel B 90 mm Hg 15 mm Hg 80 mm Hg 50 mm Hg O Vessel A O Vessel B O Vessel A The flow rates are the same. O VesselB The flow rates are the same.Explanation / Answer
Answer 1 . Answer will be option A that is flow rate is directly proportional to pressure gradient and inversely proportional to the resistance. This is due to the poiseuilles law and equation. That is flow rate Q=3.14Pr4/8nl, where Q is flow rate, P is pressure, r is radius, n is fluid viscosity, l is length of vessel. Viscosity is the resistance of the fluid flowing in the vessels.
Answer 2 . From the above described poiseuilles equation and resistance equation that is R is proportional to nL/r4, we can answer this question.
An increase in blood viscosity (n) tends to increase resistance (R).
An increase in vessel length, tends to increase resistance.
An increase in vessel radius tends to decrease resistance.
Answer 3. From the above described equation of resistance, it is clear that the most important variable in the determination of resistance to flow is vessel radius. In maximum cases the viscosity of fluid and length of blood vessel is constant. Thus radius remains most important. Slight change in vessel radius, causes marked change in resistance to flow of the fluid as it is vivid from the equation described above.
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