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Questions and Answers
What does resistance to blood flow primarily measure?
What does resistance to blood flow primarily measure?
What is the relationship between flow rate and resistance according to the flow rate equation?
What is the relationship between flow rate and resistance according to the flow rate equation?
What is necessary to drive blood flow in the vascular system?
What is necessary to drive blood flow in the vascular system?
How is the pressure gradient (ΔP) measured?
How is the pressure gradient (ΔP) measured?
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Which of the following best describes bulk flow?
Which of the following best describes bulk flow?
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Why is adequate blood pressure critical for organs like the brain and heart?
Why is adequate blood pressure critical for organs like the brain and heart?
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Which factor can modify the magnitude of the driving force of blood flow (ΔP)?
Which factor can modify the magnitude of the driving force of blood flow (ΔP)?
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How is resistance (R) typically measured?
How is resistance (R) typically measured?
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What occurs as a result of reduced blood flow to the brain?
What occurs as a result of reduced blood flow to the brain?
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What is a defining characteristic of atherosclerosis?
What is a defining characteristic of atherosclerosis?
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Which type of blood flow is typically silent and streamlined?
Which type of blood flow is typically silent and streamlined?
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What is likely to happen if blood flow is turbulent?
What is likely to happen if blood flow is turbulent?
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Where does the pulmonary circuit carry blood?
Where does the pulmonary circuit carry blood?
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What primarily controls the rate of blood flow in tissues?
What primarily controls the rate of blood flow in tissues?
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Which law describes the relationship between blood flow and the factors it depends on?
Which law describes the relationship between blood flow and the factors it depends on?
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Which vessels carry blood away from the heart?
Which vessels carry blood away from the heart?
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What is one factor that affects resistance to blood flow?
What is one factor that affects resistance to blood flow?
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What is the primary function of the cardiovascular system's closed-loop structure?
What is the primary function of the cardiovascular system's closed-loop structure?
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Which of the following best describes the significance of elastic recoil in arteries?
Which of the following best describes the significance of elastic recoil in arteries?
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What is the end destination of the systemic circuit?
What is the end destination of the systemic circuit?
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Which of these describes venous return?
Which of these describes venous return?
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What is the role of pressure gradient (ΔP) in blood flow?
What is the role of pressure gradient (ΔP) in blood flow?
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What can decrease compliance in blood vessels?
What can decrease compliance in blood vessels?
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How do laminar and turbulent flow differ?
How do laminar and turbulent flow differ?
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What is the primary function of the elastic recoil of arterial walls during diastole?
What is the primary function of the elastic recoil of arterial walls during diastole?
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Which of the following factors does NOT affect venous return?
Which of the following factors does NOT affect venous return?
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What occurs during a deep breath that enhances venous return?
What occurs during a deep breath that enhances venous return?
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Which statement best describes the role of the skeletal muscle pump in venous return?
Which statement best describes the role of the skeletal muscle pump in venous return?
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What role does sympathetic stimulation play in venous return?
What role does sympathetic stimulation play in venous return?
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What happens to the radius of an arteriole during vasoconstriction?
What happens to the radius of an arteriole during vasoconstriction?
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Which term describes the combined resistance of all blood vessels in the systemic circuit?
Which term describes the combined resistance of all blood vessels in the systemic circuit?
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How does the compliance of an artery relate to the blood vessel's response to changing blood volume?
How does the compliance of an artery relate to the blood vessel's response to changing blood volume?
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What is the elasticity of blood vessels that allows them to recoil called?
What is the elasticity of blood vessels that allows them to recoil called?
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Which type of vessels supply tissues and organs in parallel circuits?
Which type of vessels supply tissues and organs in parallel circuits?
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What happens to resistance to blood flow when the diameter of an arteriole decreases?
What happens to resistance to blood flow when the diameter of an arteriole decreases?
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What mathematical expression represents the concept of compliance in blood vessels?
What mathematical expression represents the concept of compliance in blood vessels?
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Which statement best describes elastic recoil in arteries?
Which statement best describes elastic recoil in arteries?
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What physiological change occurs due to sympathetic activation in veins?
What physiological change occurs due to sympathetic activation in veins?
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What is the relationship described by the equation MAP = CO x TPR?
What is the relationship described by the equation MAP = CO x TPR?
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Which of the following correctly describes baroreceptors?
Which of the following correctly describes baroreceptors?
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How does increased atrial pressure affect cardiac output?
How does increased atrial pressure affect cardiac output?
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What is the primary physiological contributor to resistance of blood flow in arterioles?
What is the primary physiological contributor to resistance of blood flow in arterioles?
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What role do the kidneys play in mean arterial pressure regulation?
What role do the kidneys play in mean arterial pressure regulation?
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In cases of stress, how does sympathetic stimulation affect venous return?
In cases of stress, how does sympathetic stimulation affect venous return?
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What is the primary outcome of the baroreceptor reflex?
What is the primary outcome of the baroreceptor reflex?
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What is the formula for blood flow related to pressure gradient and resistance?
What is the formula for blood flow related to pressure gradient and resistance?
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Which factor contributes to increased mean arterial pressure in a person at rest?
Which factor contributes to increased mean arterial pressure in a person at rest?
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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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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.
