PSIO 532 Study Guide - Midterm Guide: Specific Volume, Cardiac Output, Blood Vessel
Graduate Physiology PSL
Flow & Resistance
➔ Be able to differentiate between flow and velocity in terms of units and concept
Velocity
o speed at which an object or fluid is moving independent of its size or volume
o units typical expressed in distance over unit time e.g. ft/s; km/hr; m/s
o instruments that display velocity measurements: speedometer, treadmill
Flow
θ speed at which a specific volume of air or fluid is moving
θ units typical expressed in volume over unit time e.g. gallons/hour; L/min; ml/s
θ instruments that display flow measurements (less common): blood flowmeter
▪ Velocity is directly proportional to flow and inversely
proportional to cross-sectional area (CSA) – the volume is
determined by the cross-sectional area
▪ In other words, if flow goes down, velocity will go down if CSA
stays
▪ constant (or increases)
▪ Conversely, if CSA goes down velocity will go up if flow stays
constant (or increases) e.g. garden hose
▪ Smaller vessels have higher velocity
▪ Changes in flow (cardiac output) and CSA on arterial side regulate
pressure and flow since pressure is much higher in arteries
▪ CSA expands as the arteries branch further and further into
capillaries decreases velocity; the cross-sectional area COLLECTIVELY
from all the capillaries is much larger than the aorta
▪ Slow velocity facilitates exchange of nutrients, O2, CO2 and waste
▪ Changes in CSA change flow on venous side (i.e. venous return); the blood starts going
back in venules (small CSA) and then it turns into the vena cava (larger CSA)
➔ Understand the relationship between pressure, flow, and resistance in the vasculature
and be able to calculate for one variable if the other two are known. Apply this
relationship to the arteries, arterioles, capillaries, venules, and veins. Explain how blood
flow to any organ is altered by changes in resistance to that organ
Blood flow is determined by two factors (which are comparable to blowing up a
balloon)
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Document Summary
Be able to differentiate between flow and velocity in terms of units and concept. Velocity: speed at which an object or fluid is moving independent of its size or volume, units typical expressed in distance over unit time e. g. ft/s; km/hr; m/s instruments that display velocity measurements: speedometer, treadmill. Speed at which a specific volume of air or fluid is moving. Units typical expressed in volume over unit time e. g. gallons/hour; l/min; ml/s instruments that display flow measurements (less common): blood flowmeter. Understand the relationship between pressure, flow, and resistance in the vasculature and be able to calculate for one variable if the other two are known. Apply this relationship to the arteries, arterioles, capillaries, venules, and veins. Explain how blood flow to any organ is altered by changes in resistance to that organ. P (pressure difference) = q (flow) x r (resistance) Increasing resistance (e. g. , by arteriolar vasoconstriction) decreases flow, and decreasing resistance (e. g. , by arteriolar vasodilation) increases flow.
