Blood Flow and Velocity Principles
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Questions and Answers

What happens to blood flow as the pressure difference between the ends of a vessel increases?

  • Blood flow becomes turbulent.
  • Blood flow remains constant.
  • Blood flow increases. (correct)
  • Blood flow decreases.

    • In laminar flow, where is the velocity of the fluid highest?

  • At the exit of the vessel.
  • At the edges of the vessel.
  • At the entrance of the vessel.
  • In the middle of the vessel. (correct)

    • How does viscosity affect the mean velocity of fluid in a tube?

  • Viscosity has no effect on mean velocity.
  • Higher viscosity decreases mean velocity. (correct)
  • Viscosity varies mean velocity by changing the vessel diameter.
  • Higher viscosity increases mean velocity.

    • What relationship exists between mean velocity and the radius of a tube?

    <p>Mean velocity is directly proportional to the radius squared.</p> Signup and view all the answers

    What characterizes turbulent flow compared to laminar flow?

    <p>Fluid tumbles over causing increased resistance.</p> Signup and view all the answers

    What is the impact of increasing the cross-sectional area of a vessel on mean velocity?

    <p>Mean velocity increases as the radius allows more fluid to pass.</p> Signup and view all the answers

    What is the primary factor affecting flow resistance in a blood vessel?

    <p>The viscosity of the fluid.</p> Signup and view all the answers

    When the flow remains constant but the radius of the tube changes, what happens to velocity?

    <p>Velocity varies along the length of the tube.</p> Signup and view all the answers

    What happens to the average velocity of fluid as viscosity increases in laminar flow?

    <p>Average velocity decreases.</p> Signup and view all the answers

    What defines the term 'flow' in the context of fluid dynamics?

    <p>The volume of fluid passing a given point per unit time.</p> Signup and view all the answers

    What structure in the heart generates action potentials at regular intervals?

    <p>Sino-atrial node</p> Signup and view all the answers

    During which phase of the cardiac cycle does the heart muscle contract and blood is ejected into the arteries?

    <p>Ventricular systole</p> Signup and view all the answers

    What causes the closure of the atrioventricular valves during the cardiac cycle?

    <p>Increased ventricular pressure</p> Signup and view all the answers

    What is the approximate duration of a single contraction during systole?

    <p>280 ms</p> Signup and view all the answers

    Which heart sound is associated with the closure of the atrioventricular valves?

    <p>Lup</p> Signup and view all the answers

    What is the relationship between stroke volume and cardiac output?

    <p>Cardiac output equals stroke volume times heart rate</p> Signup and view all the answers

    What causes a heart murmur during the rapid ejection phase of ventricular systole?

    <p>Narrowed outflow valve</p> Signup and view all the answers

    Which phase of the cardiac cycle follows isovolumetric contraction?

    <p>Ventricular systole</p> Signup and view all the answers

    What occurs at the atrioventricular node during the spread of excitation in the heart?

    <p>A brief delay of about 120 ms</p> Signup and view all the answers

    How long does the interval from the first to second heart sound approximately last at rest?

    <p>280 ms</p> Signup and view all the answers

    What happens to pressure if resistance increases while flow remains constant?

    <p>Pressure increases</p> Signup and view all the answers

    Which statement accurately describes blood flow through vessels of varying sizes?

    <p>It is easier to push blood through larger vessels.</p> Signup and view all the answers

    What is the effect of connecting blood vessels in series versus in parallel?

    <p>Series connections result in higher total resistance.</p> Signup and view all the answers

    What occurs to flow when pressure is constant and resistance increases?

    <p>Flow decreases</p> Signup and view all the answers

    Which blood vessel type is associated with low resistance and minimal pressure drop?

    <p>Arteries</p> Signup and view all the answers

    What structural feature allows vessels to change resistance as pressure varies?

    <p>Distensible walls</p> Signup and view all the answers

    What phenomenon might occur in blood flow due to vessel narrowing?

    <p>Turbulent flow</p> Signup and view all the answers

    What is the primary factor affecting pressure in the arteries?

    <p>Resistance of the arterioles</p> Signup and view all the answers

    What happens to blood flow through distensible vessels as internal pressure rises?

    <p>More blood flows in than out.</p> Signup and view all the answers

    What is the effect of blood cells congregating in the center of the flow?

    <p>Increased apparent viscosity</p> Signup and view all the answers

    Study Notes

    Blood Flow

    • The flow of blood through blood vessels is driven by a pressure gradient.
    • Flow is proportional to the pressure difference between the ends of a vessel.
    • The higher the pressure difference the greater the flow.
    • The flow for a given pressure gradient is determined by the resistance of the vessel.
    • The flow is determined by the nature of the fluid and the vessel.

    Definitions of Flow and Velocity

    • Flow: The volume of fluid passing a given point per unit time.
    • Velocity: The rate of movement of fluid particles along the tube.

    Flow, Velocity, and Surface Area

    • Flow is constant at all points along a vessel.
    • Velocity can vary along the length if the radius of the tube changes.
    • At a given flow, velocity is inversely proportional to surface area.

    Laminar Flow

    • In most blood vessels, flow is laminar.
    • There is a gradient of velocity from the middle to the edge of the vessel, with the highest velocity in the center.
    • Fluid is stationary at the edge.

    Turbulent Flow

    • As mean velocity increases, flow eventually becomes turbulent.
    • The velocity gradient breaks down and fluid tumbles over.
    • Flow resistance is greatly increased.

    Viscosity

    • In laminar flow, the fluid moves in concentric layers.
    • The middle layers move faster than the edge layers.
    • Viscosity is the extent to which fluid layers resist sliding over one another.
    • The higher the viscosity, the slower the central layers will flow.

    Radius and Flow Resistance

    • Viscosity determines the slope of the gradient of velocity.
    • At a constant gradient, the wider the tube the faster the middle layers move, so mean velocity is proportional to the cross-sectional area of the tube.

    Poiseuille’s Law

    • Mean velocity is inversely proportional to viscosity.
    • Mean velocity is directly proportional to surface area.
    • Flow is the product of mean velocity and surface area.
    • Flow = D P x r2 x r2/(viscosity x length)

    Resistance in Series and Parallel

    • In series resistances combine just like electrical resistances.
    • In parallel resistances combine by the formula: R=(R1xR2)/(R1+R2)

    Pressure, Flow, and Resistance

    • If flow is fixed, the higher the resistance the greater the change in pressure from one end of the vessel to the other.
    • If pressure is fixed, the higher the resistance the lower the flow.

    The Whole Circulation

    • Over the whole circulation, flow is the same at all points.
    • Arteries are low resistance; pressure drop over arteries is small.
    • Arterioles are high resistance; pressure drop over arterioles is large.
    • The overall resistance of capillaries is low, due to many connected in parallel. The pressure drop over capillaries is low.
    • Venues and veins are low resistance; pressure drop over venules and veins is low.
    • The pressure within arteries is high because of the high resistance of arterioles.
    • If the heart pumps more blood, and the resistance of arterioles remains the same, arterial pressure will rise.

    Special Problems of Flow in Blood Vessels

    • Flow may become turbulent in some vessels.
    • Flow becomes turbulent if a vessel is narrowed.
    • Turbulent flow generates sound.
    • Blood vessels have distensible walls which generate a transmural pressure between inside and outside.

    Distensible Vessels

    • As a vessel stretches, resistance falls.
    • The higher the pressure in a vessel, the easier it is for blood to flow through it.
    • Distensible vessels ‘store’ blood.
    • Veins are most distensible.

    The Heart

    • Two pumps in series.
    • Each side consists of a thin-walled atrium and a muscular ventricle.
    • Flows into and out of the ventricle are controlled by valves: Atrioventricular valves (mitral & tricuspid) and outflow valves (aortic and pulmonary).

    Heart Muscle

    • A specialized form with discrete cells connected electrically.
    • Cells contract when an action potential is in the membrane.
    • An action potential causes a rise in intracellular calcium.
    • Action potential is long, with a single contraction lasting 280 ms - systole.
    • Action potentials are triggered by the spread of excitation from cell to cell.

    Pacemakers

    • Pacemakers generate an action potential at regular intervals.
    • One action potential spreads over the whole heart and produces a coordinated contraction.

    Phases of the Cardiac Cycle

    • Systole - the interval between beats is diastole.

    Spread of Excitation

    • Pacemaker in the sinoatrial node (right atrium).
    • Activity first spreads over the atria (atrial systole).
    • The activity is delayed about 120 ms in reaching the atrioventricular node.
    • From the a-v node, the activity spreads down the septum between the ventricles, then spreads through the ventricular myocardium from inner (endocardial) to outer (epicardial) surface.
    • The ventricle contracts from the apex up, forcing blood towards the outflow valves

    The Cardiac Cycle

    • At rest, the SA node generates an action potential about once a second.
    • This produces a short atrial systole, followed by a longer ventricular systole.
    • Ventricular systole lasts about 280 ms, followed by a relaxation lasting about 700 ms before the next systole.

    The Left Ventricle

    • Inflow valve - the mitral valve.
    • Opens when atrial pressure exceeds intraventricular pressure.
    • Closes when ventricular pressure exceeds atrial pressure.
    • Outflow valve - the aortic valve.
    • Opens when intra-ventricular pressure exceeds aortic pressure.
    • Closes when aortic pressure exceeds ventricular pressure.

    The Cardiac Cycle

    • Start: Towards the end of ventricular systole.
      • Ventricles are contracted.
      • Intra-ventricular pressure is high.
      • Outflow valves are open.
      • Blood flows into the arteries.
      • Ventricular pressure > atrial pressure, so a/v valves are closed.
    • Ventricles begin to relax: Intra-ventricular pressure falls.
      • Intra-ventricular pressure becomes < arterial pressure.
      • Brief backflow closes outflow valves.
      • All valves are now closed: get isovolumetric relaxation.
    • During systole, blood has continued to return to the atria: Atrial pressure is relatively high.
      • As intra-ventricular pressure falls, eventually atrial pressure > intra-ventricular pressure.
      • So, a/v valves open.
    • With a/v valves open, ventricles fill rapidly (Rapid filling phase).
      • This lasts about 200-300 ms.
      • Most filling of ventricles occurs in this phase.
    • As diastole continues, the ventricles fill more slowly:
      • Intraventricular pressure rises as ventricular walls stretch.
      • Intra-ventricular pressure matches atrial pressure and filling stops.
    • Atrial systole:
      • Forces a small extra amount of blood into the ventricles.
      • However, the heart pumps perfectly well without atrial systole.
    • Ventricular systole:
      • Intraventricular pressure rises very rapidly.
      • Intraventricular pressure > atrial pressure.
      • After brief backflow, a/v valves close.
      • All valves are closed: get isovolumetric contraction.
      • Intraventricular pressure > arterial pressure which has been falling in diastole, so outflow valves open.
      • As outflow valves open, blood is ejected rapidly into the arteries (Rapid ejection phase).
      • Arterial pressure rises rapidly.
      • As arterial pressure rises, the rate of ejection of blood falls.
      • Both arterial and intraventricular pressures peak towards the end of systole.
      • Outflow eventually ceases with blood remaining in the ventricle.
      • Eventually, systole ends, and the cycle restarts.

    Heart Sounds

    • Two main sounds associated with the valves closing.
      • First sound - ‘lup’ - closure of a/v valves.
      • Second sound - ‘dup’- closure of outflow valves.
    • The first sound occurs at the onset of ventricular systole.
    • The second sound occurs at the end of ventricular systole.
    • At rest, the interval from the 1st to the 2nd sound is about 280 ms.
    • The interval from the 2nd sound to the next 1st sound is 700 ms.

    Heart Murmurs

    • Turbulent flow of blood generates murmurs.
    • Murmurs occur when blood flow is highest.
    • Narrowed valve - stenosis.
    • Valve not closing properly - incompetence.

    Cardiac Output

    • The heart ejects a stroke volume with each beat.
    • Cardiac output is stroke volume multiplied by heart rate.
    • At rest: 80 ml x 60, ie, c. 5 l.min-1

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    Applied Cardiac Physiology Lecture 1 PDF

    Description

    Explore the essential principles of blood flow and velocity in this quiz. Learn how pressure gradients, vessel characteristics, and fluid properties affect flow and velocity. This quiz will test your understanding of laminar flow and its implications in the circulatory system.

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