Lecture 6: Pressure and Blood Flow
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Questions and Answers

What does resistance to blood flow primarily measure?

  • The friction that impedes blood flow (correct)
  • The volume of blood pumped per minute
  • The variation in blood pressure
  • The speed of blood circulation

    • What is the relationship between flow rate and resistance according to the flow rate equation?

  • Flow rate is inversely proportional to resistance (correct)
  • Flow rate is directly proportional to resistance
  • Flow rate equals resistance
  • Flow rate is independent of resistance

    • What is necessary to drive blood flow in the vascular system?

  • Minimal resistance to blood flow
  • Constant blood temperature
  • A positive pressure gradient (correct)
  • A negative pressure gradient

    • How is the pressure gradient (ΔP) measured?

    <p>In mmHg (D)</p> Signup and view all the answers

    Which of the following best describes bulk flow?

    <p>Movement of fluid from higher pressure to lower pressure (C)</p> Signup and view all the answers

    Why is adequate blood pressure critical for organs like the brain and heart?

    <p>To ensure adequate perfusion (B)</p> Signup and view all the answers

    Which factor can modify the magnitude of the driving force of blood flow (ΔP)?

    <p>Hormones and nervous systems (B)</p> Signup and view all the answers

    How is resistance (R) typically measured?

    <p>Both B and C (D)</p> Signup and view all the answers

    What occurs as a result of reduced blood flow to the brain?

    <p>Cellular death leading to stroke (B)</p> Signup and view all the answers

    What is a defining characteristic of atherosclerosis?

    <p>Buildup of plaque in the arteries (B)</p> Signup and view all the answers

    Which type of blood flow is typically silent and streamlined?

    <p>Laminar flow (C)</p> Signup and view all the answers

    What is likely to happen if blood flow is turbulent?

    <p>Audible sound may occur (C)</p> Signup and view all the answers

    Where does the pulmonary circuit carry blood?

    <p>From the right ventricle to the lungs (D)</p> Signup and view all the answers

    What primarily controls the rate of blood flow in tissues?

    <p>Tissue demand for nutrients and oxygen (B)</p> Signup and view all the answers

    Which law describes the relationship between blood flow and the factors it depends on?

    <p>Poiseuille’s law (D)</p> Signup and view all the answers

    Which vessels carry blood away from the heart?

    <p>Arteries (C)</p> Signup and view all the answers

    What is one factor that affects resistance to blood flow?

    <p>Elasticity of the blood vessels (C)</p> Signup and view all the answers

    What is the primary function of the cardiovascular system's closed-loop structure?

    <p>To confine blood within the vascular system (A)</p> Signup and view all the answers

    Which of the following best describes the significance of elastic recoil in arteries?

    <p>It maintains blood pressure during the cardiac cycle (A)</p> Signup and view all the answers

    What is the end destination of the systemic circuit?

    <p>Right atrium (A)</p> Signup and view all the answers

    Which of these describes venous return?

    <p>The volume of blood returning to the heart (C)</p> Signup and view all the answers

    What is the role of pressure gradient (ΔP) in blood flow?

    <p>It denotes the force that pushes blood through the vessel (D)</p> Signup and view all the answers

    What can decrease compliance in blood vessels?

    <p>Atherosclerosis or arterial stiffness (B)</p> Signup and view all the answers

    How do laminar and turbulent flow differ?

    <p>Laminar flow is smooth and orderly, while turbulent flow is chaotic. (C)</p> Signup and view all the answers

    What is the primary function of the elastic recoil of arterial walls during diastole?

    <p>To maintain arterial pressure and push blood forward (D)</p> Signup and view all the answers

    Which of the following factors does NOT affect venous return?

    <p>Blood vessel diameter (C)</p> Signup and view all the answers

    What occurs during a deep breath that enhances venous return?

    <p>Pressure drop creates a sucking effect towards the heart (C)</p> Signup and view all the answers

    Which statement best describes the role of the skeletal muscle pump in venous return?

    <p>It works in conjunction with one-way valves. (C)</p> Signup and view all the answers

    What role does sympathetic stimulation play in venous return?

    <p>It causes venoconstriction. (D)</p> Signup and view all the answers

    What happens to the radius of an arteriole during vasoconstriction?

    <p>It decreases. (A)</p> Signup and view all the answers

    Which term describes the combined resistance of all blood vessels in the systemic circuit?

    <p>Total peripheral resistance (TPR) (A)</p> Signup and view all the answers

    How does the compliance of an artery relate to the blood vessel's response to changing blood volume?

    <p>It indicates how easily the artery can expand. (D)</p> Signup and view all the answers

    What is the elasticity of blood vessels that allows them to recoil called?

    <p>Elastance (B)</p> Signup and view all the answers

    Which type of vessels supply tissues and organs in parallel circuits?

    <p>Arteries (D)</p> Signup and view all the answers

    What happens to resistance to blood flow when the diameter of an arteriole decreases?

    <p>Resistance increases. (C)</p> Signup and view all the answers

    What mathematical expression represents the concept of compliance in blood vessels?

    <p>Compliance = Δ Volume / Δ Pressure (A)</p> Signup and view all the answers

    Which statement best describes elastic recoil in arteries?

    <p>It is the tendency of arteries to return to original shape after stretching. (D)</p> Signup and view all the answers

    What physiological change occurs due to sympathetic activation in veins?

    <p>Venoconstriction (C)</p> Signup and view all the answers

    What is the relationship described by the equation MAP = CO x TPR?

    <p>Mean arterial pressure equals cardiac output times total peripheral resistance. (B)</p> Signup and view all the answers

    Which of the following correctly describes baroreceptors?

    <p>Function through negative feedback mechanisms (C)</p> Signup and view all the answers

    How does increased atrial pressure affect cardiac output?

    <p>It increases end-diastolic pressure leading to increased cardiac output. (D)</p> Signup and view all the answers

    What is the primary physiological contributor to resistance of blood flow in arterioles?

    <p>Radius or diameter of the arterioles (C)</p> Signup and view all the answers

    What role do the kidneys play in mean arterial pressure regulation?

    <p>They cooperate with the heart and blood vessels. (B)</p> Signup and view all the answers

    In cases of stress, how does sympathetic stimulation affect venous return?

    <p>It enhances venous return. (A)</p> Signup and view all the answers

    What is the primary outcome of the baroreceptor reflex?

    <p>To regulate mean arterial pressure through feedback. (B)</p> Signup and view all the answers

    What is the formula for blood flow related to pressure gradient and resistance?

    <p>F = ΔP / R (B)</p> Signup and view all the answers

    Which factor contributes to increased mean arterial pressure in a person at rest?

    <p>Reduced venous is compliance (D)</p> Signup and view all the answers

    Study Notes

    Lecture 6: Pressure, Force and Elasticity

    • Lecturer: Dr. Isabel Hwang, Senior Lecturer
    • Department: Division of Education, School of Biomedical Sciences, Faculty of Medicine, CUHK
    • Email: [email protected]
    • Office number: 3943 6795

    Lecture Outline

    • Flow rate equation
    • Types of blood flow (laminar vs. turbulent)
    • Pulmonary and systemic circuits
    • Poiseuille's law
    • Factors affecting resistance (R) to blood flow
    • Blood pressure and its importance (arterial)
    • Compliance and elastance of arteries and veins
    • Physiological significance of elastic recoil in elastic artery during cardiac cycle
    • Factors affecting venous return (VR)

    Introduction

    • Blood flow rate through tissues controlled by tissue demand for nutrients and oxygen (e.g., during exercise)
    • Cardiovascular system (heart, blood vessels, and blood) constantly maintains pressure gradient driving blood to organs.

    Blood flow through a blood vessel

    • Determined by two factors:
      • Pressure difference (gradient) between vessel ends
      • Resistance to blood flow (friction)

    Driving force of blood flow

    • Ohm's law (flow rate equation): F = ΔP / R
      • ΔP: pressure gradient created by cardiac contractions. Modified by homeostatic control through hormones, nervous systems, etc.

    The flow rate equation

    • Flow (F) is directly proportional to pressure difference (ΔP) and inversely proportional to resistance (R)
      • F = ΔP/R
      • ΔP is measured in mmHg
      • R is measured in mmHg/mL/min or mmHg/L/min
    • Bulk flow: movement of fluid or gases from high to low pressure

    Pressure gradients

    • ΔP is the difference in pressure between relevant points within the vascular system—not absolute pressure.
    • Examples:
      • P1 = 100 mmHg, P2 = 10 mmHg, ΔP = 90 mmHg
      • P1 = 500 mmHg, P2 = 410 mmHg, ΔP = 90 mmHg.
    • Positive pressure gradient needed to drive blood flow

    Importance of blood pressure

    • Adequate blood pressure is essential for maintaining and driving blood flow.
    • Critical organs like the brain and heart rely on steady blood supply to function.
    • Reduced blood flow to organs results in reduced glucose and oxygen delivery, causing potential organ damage (e.g., stroke, heart attack)
    • Atherosclerosis: thickening or hardening of arteries due to plaque buildup in the inner lining

    Two types of blood flow (laminar vs. turbulent)

    • Laminar flow: smooth, streamlined flow through long, smooth vessels. Velocity is greater in the center of blood vessel.
    • Turbulent flow: disrupted, non-streamlined flow due to high velocity or obstructions. Audible sound (bruit) in damaged/blocked blood vessels.

    Turbulence in leaky or stenotic (narrowed) cardiac valves

    • Laminar flow—quiet
    • Turbulent flow—murmur (in diseased valves)

    The cardiovascular system

    • Closed-loop system: blood contained within vascular system (systemic and pulmonary circuits).

    Pulmonary and systemic circuits

    • Pulmonary circuit: right ventricle → lungs → left atrium

    • Systemic circuit: left ventricle → peripheral organs/tissues → right atrium

    • In both circuits, the blood vessels carrying blood away from the heart are called arteries.

    • Those carrying blood to the heart are called veins.

    Pressure gradients

    • Pulmonary circuit: ≈15 mmHg
    • Systemic circuit: ~ 85mmHg

    Resistance in the CV system

    • Poiseuille's law: R = (8Ln) / (πr^4)
      • L = vessel length
      • n = fluid viscosity
      • r = vessel internal radius
    • Resistance increased by smaller radius (inversely related like 1/r^4), and length.

    Effect of tube radius on flow

    • Decreasing radius two-fold increases resistance sixteen-fold.
    • If ΔP constant, flow decreases sixteen-fold.

    Resistance in the CV system

    • Factors affecting resistance:
      • Radius of vessel (r): largest contributor. Resistance increased by constriction and atherosclerosis, decreased by relaxation and dilation
      • Length of vessel (L): total number of vessels. Resistance increases with more vessels, Obesity increases vascular length
      • Viscosity of fluid (η): Blood viscosity determined by amount of red blood cells, proteins, and temperature

    Five types of blood vessels in the vascular system

    • Arteries, arterioles, capillaries, venules, veins

    Resistance in the CV system

    • Effect of arteriolar radius on resistance and blood flow: vasoconstriction decreases radius, increasing resistance vasodilation increases radius, decreasing resistance

    Example: what happens to resistance (R) if smooth muscle cells in the arteriole contract?

    • Contraction causes vasoconstriction, reducing radius and increasing resistance to blood flow.

    Resistance in the CV system

    • Total peripheral resistance (TPR): combined resistance within the systemic circuit, especially arterioles. Resistance across network varies. Arteries supply tissues in parallel circuits.

    Arteries and veins

    • Arteries have low compliance (high elastance, recoil) helping smooth blood flow and maintaining pressure.
    • Veins have high compliance ( low elastance), stretching readily.

    Venous return

    • Return of blood to right atrium via veins
    • Improves end-diastolic volume, stroke volume, cardiac output
    • Dependent on:
      • Blood volume and venous pressure
      • Skeletal muscle pumps
      • Pressure drop during inhalation
      • Venoconstriction (sympathetic stimulation)

    The skeletal muscle pump and one-way valves

    • Skeletal muscle contractions and one-way valves improve venous return.

    Venous return cannot be facilitated by skeletal muscle pump alone

    • Without valves the flow is both directions when muscle contracts.

    The respiratory pump

    • Pressure differences during breathing
    • Creates upward "sucking" effect, pulling blood toward the heart.

    Real-life example: physiological significance of modified veins compliance

    • Stress (sympathetic activation) leads to venoconstriction, reducing venous compliance, improving venous return, increasing venous pressure, and increasing blood flow to the right atrium, increasing end-diastolic volume, stroke volume, cardiac output, mean arterial pressure.

    Factors affecting venous pressure and mean arterial pressure (MAP)

    • Elaborated in later lecture.

    If we just consider the systemic circuit

    • F = ΔP/R
    • ΔP = F x R
    • MAP = CO x TPR

    Homeostatic regulation of MAP

    • Requires heart, blood vessels, kidneys
    • Supervised by the brain
    • Changes in one variable are compensated by others

    Short-term and long-term regulation of MAP

    • Fast response through cardiovascular system
    • Slow response through kidneys (fluid excretion)
    • Blood pressure fluctuations: counteract by cardiovascular and renal system

    The baroreceptor reflex

    • Short-term regulation of MAP
    • Located in carotid arteries and aortic arch and walls of large neck and thoracic arteries
    • Integrated into medulla oblongata in the brainstem
    • Negative feedback—functions through negative feedback—change in one variable is compensated for by other variables

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    Pressure, Force and Elasticity Lecture Notes (Oct 2024) PDF

    Description

    Explore the principles of pressure, force, and elasticity in the cardiovascular system in this detailed quiz. Focus on blood flow dynamics, resistance factors, and the physiological significance of arterial compliance and elastic recoil. Perfect for students of biomedical sciences.

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