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Questions and Answers
What is the average pressure driving blood forward into the tissues throughout the cardiac cycle known as?
What is the average pressure driving blood forward into the tissues throughout the cardiac cycle known as?
Which pressure measurement is defined as the pressure exerted in the arteries during the heart's contraction?
Which pressure measurement is defined as the pressure exerted in the arteries during the heart's contraction?
Which mechanism primarily regulates blood pressure by responding to the stretch of blood vessels?
Which mechanism primarily regulates blood pressure by responding to the stretch of blood vessels?
What effect does arteriolar vasoconstriction have on blood pressure?
What effect does arteriolar vasoconstriction have on blood pressure?
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Which of the following causes hypertension due to increase in blood volume?
Which of the following causes hypertension due to increase in blood volume?
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What primarily determines mean arterial blood pressure?
What primarily determines mean arterial blood pressure?
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Which hormone is associated with increasing both vasoconstriction and blood volume?
Which hormone is associated with increasing both vasoconstriction and blood volume?
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What defines primary hypertension?
What defines primary hypertension?
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Which factor does NOT contribute to total peripheral resistance?
Which factor does NOT contribute to total peripheral resistance?
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What is a hallmark of hypertension?
What is a hallmark of hypertension?
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Which of the following statements about hypotension is correct?
Which of the following statements about hypotension is correct?
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In long-term regulation of blood pressure, which aspect is primarily controlled?
In long-term regulation of blood pressure, which aspect is primarily controlled?
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What is a common consequence of secondary hypertension?
What is a common consequence of secondary hypertension?
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What is the primary function of capillaries in the circulatory system?
What is the primary function of capillaries in the circulatory system?
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Which mechanism primarily induces vasoconstriction in arterioles?
Which mechanism primarily induces vasoconstriction in arterioles?
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How does a decrease in blood pressure affect arterioles?
How does a decrease in blood pressure affect arterioles?
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What role do hormones like norepinephrine and epinephrine play in the regulation of arteriolar radius?
What role do hormones like norepinephrine and epinephrine play in the regulation of arteriolar radius?
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Which phenomenon is referred to as autoregulation?
Which phenomenon is referred to as autoregulation?
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What occurs when sympathetic vasoconstrictor activity decreases?
What occurs when sympathetic vasoconstrictor activity decreases?
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What is the effect of exercise on intrinsic control mechanisms of arterioles?
What is the effect of exercise on intrinsic control mechanisms of arterioles?
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What happens to arterioles during low blood flow conditions?
What happens to arterioles during low blood flow conditions?
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Study Notes
Human Physiology BIOL3205 - Cardiovascular System II
- Course taught by Prof. Chi Bun Chan at the School of Biological Sciences, 5N10 Kadoorie Biological Sciences Building, University of Hong Kong
- Contact email: [email protected]
- Contact phone number: 39173823
Lecture Outline
- Structure of blood vessels
- Regulation of blood flow
- Mechanism of material exchange between cells and capillaries
- Physical characteristics of blood pressure
- Regulation of blood pressure
- Hypertension and hypotension
Parallel Flow
- Blood flows in a parallel arrangement
- Advantages:
- Receives the same composition
- Blood flow in each organ can be independently adjusted (e.g., exercise)
- Constant blood flow to the brain
Types of Blood Vessels
- Hollow interior (lumen)
- Classified by blood flow direction and size
- Five types: arteries, arterioles, capillaries, venules, and veins
- Microcirculation: arterioles, capillaries, venules
- Contains endothelium, elastin fibers, smooth muscle, connective tissues
- Veins have valves
Arteries
- Major pathway for transporting blood between organs
- Offer little resistance due to large radius
- Composed of connective tissues:
- Collagen fibers (tensile strength)
- Elastin (elasticity)
- Act as pressure reservoirs to maintain continuous blood flow
Arterioles
- An artery branches into numerous arterioles within the organ
- Lack elastin fibers—no elasticity
- Have smooth muscle to control radius
- Vasodilation: enlargement of the vessel lumen
- Vasoconstriction: narrowing of the vessel lumen
- Partially constricted at basal condition (vascular tone), forming basal resistance
Change of Blood Flow Distribution
- Blood flow is not evenly distributed to all organs, but based on need
- Vasoconstriction and vasodilation control cardiac output distribution
- Contributes to total peripheral resistance (TPR)
Control of Blood Flow - Arteriolar Radius
- Arteriole radius is regulated by intrinsic and extrinsic control
- Intrinsic control: local metabolic need
- Extrinsic control: overall blood pressure
- Intrinsic control overrides extrinsic control (e.g., muscle)
Intrinsic Control of Arteriolar Radius - Chemical Factors
- Local chemical influences on arteriolar smooth muscles are related to metabolic changes
- Active hyperemia: increased blood flow in response to enhanced tissue activity
- Reactive hyperemia: increased blood flow in response to lack of blood flow
- Vasoactive paracrines (e.g., NO and endothelin) released from endothelial cells in response to metabolic changes
Intrinsic Control of Arteriolar Radius - Physical Factors
- Arteriolar smooth muscle is stretch-sensitive
- Responds to passive stretch (e.g., high blood pressure) by myogenically increasing tone (vasoconstriction)
- During low blood flow, arterioles relax (vasodilation)
- Maintains constant blood volume
- Together with chemical mechanism (reactive hyperemia) form autoregulation
Arteriole Radius and Blood Flow
- Normal vascular tone, increase in blood pressure leads to vasoconstriction, drop in blood pressure leads to vasodilation
Extrinsic Control of Arteriolar Radius
- Arteriolar smooth muscle is innervated by sympathetic nerves
- Release of norepinephrine causes vasoconstriction
- No parasympathetic nerves
- Vasodilation is produced by decreasing sympathetic vasoconstrictor activity
- Hormones (e.g., norepinephrine, epinephrine, vasopressin, angiotensin II) released from other endocrine organs regulate arteriolar radius and blood flow
- Can be overridden by intrinsic control (e.g., exercise)
Capillaries
- Thinnest and smallest vessels (~the size of a red blood cell), containing a single layer of endothelial cells
- Primary function: substance exchange between blood and tissues
- Capillary wall is thin and has pores
- Extensive branching (cells within 1 mm from capillaries) -> high surface area (~600 m²)
- Slow blood velocity (not flow rate) which provides adequate time for material exchange
Materials Exchange between Blood and Cells
- Exchange occurs between blood and cells through interstitial fluid
- Materials cross via passive diffusion (lipid-soluble molecules) or bulk flow (water-soluble substances and plasma proteins) through pores, and by facilitated diffusion across the vessel membrane
Bulk Flow
- A volume of protein-free plasma filters out of the capillary, mixes with interstitial fluid, and is reabsorbed by the blood
- Fluid is pushed out through capillary pores via ultrafiltration
- Net inward movement of interstitial fluid back into capillaries is called reabsorption
- Controlled by capillary blood pressure (Pc) and plasma-colloid osmotic pressure (πp) differences between plasma and interstitial fluid
Metarterioles
- Structural intermediates between arterioles and capillaries
- Contain isolated rings of smooth muscle (precapillary sphincters) acting as gatekeepers
- Regulated by local metabolic changes
- Regulation of blood flow through a particular organ
- Blood flow to a particular tissue at constant blood pressure is controlled by degree of resistance offered by arterioles (sympathetic and local factors) and the number of open capillaries (local factors)
Veins
- Thin-walled vessels with little tone and resistance (due to large radius)
- Highly stretchable with little elastic recoil
- Pathway for blood return to the heart, acting as a blood reservoir
- Contain valves
- Venous return mechanisms: sympathetic activity, skeletal muscle activity, respiratory pump, cardiac suction
Mechanisms of Venous Return
- Skeletal muscle pumps
- Respiratory pump
- Cardiac suction
Blood Pressure
- Force exerted by blood against vessel walls
- Usually refers to arterial pressure
- Dependent on cardiac output, blood volume, arterial compliance/distensibility, and total peripheral resistance (TPR)
- Systolic pressure: maximum pressure during systole (~120 mm Hg)
- Diastolic pressure: minimum pressure during diastole (~80 mm Hg)
- Mean arterial pressure (MAP): average pressure driving blood forward (~93 mm Hg)
Pressure in Different Blood Vessels
- Blood pressure in arteries is pulsatile, not static
- Pressure gradient encourages blood flow from the heart to other organs
- Blood pressure is a function of vessel resistance
Sphygmomanometer
- Device used to measure blood pressure (using inflated cuff around the arm)
- Korotkoff sounds (produced by blood flow through compressed artery) indicate blood pressure
Regulation of Blood Pressure - Baroreceptors
- Blood pressure fluctuates based on external stimuli (e.g., temperature, exercise)
- Monitored by baroreceptors (mechanoreceptors)
- Stretch of blood vessels triggers increased action potential generation rates, providing information to the central nervous system
- Integrating center: cardiovascular control center
Regulation of Blood Pressure
- Short-term regulation (seconds): controls cardiac output and total peripheral resistance (TPR)
- Long-term regulation (minutes-days): controls blood volume and TPR
- Hormonal factors (e.g., epinephrine, vasopressin, angiotensin II) regulate vasoconstriction and urine output
- Blood volume influences blood pressure
Determinants of Mean Arterial Blood Pressure
- Cardiac output (heart rate and stroke volume)
- Total peripheral resistance (arteriolar radius)
- Blood viscosity/blood volume
Short-Term Regulation of Blood Pressure
- Parasympathetic stimulation lowers heart rate
- Sympathetic stimulation raises heart rate, contractile strength of the heart, vasoconstriction to all blood vessels, and venous return
- Arteriolar and venous vasoconstriction (to raise TPR and venous return)
Hypertension
- Long-term elevated arterial blood pressure (140/90 mm Hg or higher)
- Can lead to various complications (e.g., stroke, heart attack, kidney failure, etc.)
- Primary (unknown cause) or secondary (other disease)
- Self-perpetuating (positive feedback loop)
Hypotension
- Disproportion between vascular capacity and blood volume; or the heart being too weak to circulate blood effectively
- Causes: hemorrhage, heart failure, etc., potentially leading to circulatory shock (reversible or irreversible)
After the Lecture, You Should Be Able to Explain
- Anatomical differences between blood vessels
- Regulation of blood flow (arteriole radius changes)
- Mechanism of material exchange between cells and capillaries
- Physical characteristics of blood pressures
- Regulation of blood pressure
- Blood pressure disorders
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Description
Dive into the intricacies of the cardiovascular system in this quiz based on the Human Physiology BIOL3205 course. Explore topics like blood vessel structure, blood flow regulation, and the mechanisms governing material exchange. Test your understanding of essential concepts such as hypertension, hypotension, and microcirculation.
