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Questions and Answers
What primarily drives the movement of blood through the vessels?
What primarily drives the movement of blood through the vessels?
How is blood pressure defined in relation to blood vessels?
How is blood pressure defined in relation to blood vessels?
Which of the following factors does NOT influence blood flow through the vessels?
Which of the following factors does NOT influence blood flow through the vessels?
What effect does increased pressure within a vessel have on blood flow?
What effect does increased pressure within a vessel have on blood flow?
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Which statement is true regarding the relationship between blood pressure and vessel walls?
Which statement is true regarding the relationship between blood pressure and vessel walls?
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What phenomenon occurs when red blood cells (RBC) accumulate along the axis of a blood vessel?
What phenomenon occurs when red blood cells (RBC) accumulate along the axis of a blood vessel?
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How does plasma skimming affect blood viscosity?
How does plasma skimming affect blood viscosity?
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What happens to hematocrit levels as blood approaches a micro-vessel due to plasma skimming?
What happens to hematocrit levels as blood approaches a micro-vessel due to plasma skimming?
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What role does plasma skimming play in microvascular blood flow?
What role does plasma skimming play in microvascular blood flow?
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What is the mean pulmonary arterial pressure in the pulmonary circulation?
What is the mean pulmonary arterial pressure in the pulmonary circulation?
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What is the mean left atrial pressure in the pulmonary circulation?
What is the mean left atrial pressure in the pulmonary circulation?
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What is the net pressure difference calculated in the pulmonary circulation?
What is the net pressure difference calculated in the pulmonary circulation?
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Which statement about mean pressures in pulmonary circulation is correct?
Which statement about mean pressures in pulmonary circulation is correct?
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How does the mean pulmonary arterial pressure relate to blood flow in the pulmonary circulation?
How does the mean pulmonary arterial pressure relate to blood flow in the pulmonary circulation?
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What happens to blood flow when the pressure falls below critical closing pressure?
What happens to blood flow when the pressure falls below critical closing pressure?
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What is the average diameter of red blood cells (RBC) mentioned in the context?
What is the average diameter of red blood cells (RBC) mentioned in the context?
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Why is intramural pressure significant for blood flow through capillaries?
Why is intramural pressure significant for blood flow through capillaries?
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What occurs when the intramural pressure is inadequate in the circulatory system?
What occurs when the intramural pressure is inadequate in the circulatory system?
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What is the average diameter of capillaries compared to red blood cells?
What is the average diameter of capillaries compared to red blood cells?
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What type of resistance do vascular components exhibit?
What type of resistance do vascular components exhibit?
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What initiates blood distribution to major organs?
What initiates blood distribution to major organs?
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Where do the large arteries that supply major organs originate from?
Where do the large arteries that supply major organs originate from?
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How is the resistance in a vascular bed characterized?
How is the resistance in a vascular bed characterized?
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Why do vascular components have resistance?
Why do vascular components have resistance?
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What does blood flow through the largest artery equal to?
What does blood flow through the largest artery equal to?
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Which statement best describes the relationship between blood flow in different vessels?
Which statement best describes the relationship between blood flow in different vessels?
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How does total blood flow compare through all arterioles and the capillaries?
How does total blood flow compare through all arterioles and the capillaries?
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What can be inferred about total blood flow in the circulatory system?
What can be inferred about total blood flow in the circulatory system?
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What is a characteristic of blood flow in the circulatory system?
What is a characteristic of blood flow in the circulatory system?
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Study Notes
Vascular Physiology Lecture 2
- Concept 3: Blood Viscosity
- Viscosity is defined as internal friction in fluids, or the lack of slipperiness.
- Viscosity measures the fluid's thickness and its resistance to flow.
- Viscosity can be measured in vitro using a viscometer.
- The unit of measure for viscosity is the Poise (after Poiseuille)
- A fluid with 1 poise viscosity has a force of 1 dyne/cm² of contact between layers when flowing at a 1 cm/sec velocity gradient
- 1 Poise = 0.100 kg⋅m⁻¹.s⁻¹= 1g⋅cm⁻¹.s⁻¹
- 1 Pa⋅s = 1 kg⋅m⁻¹.s⁻¹= 10 P
- Relative viscosity is more commonly used, indicating a fluid's viscosity relative to water at body temperature (37°C).
- Water viscosity at 21°C is 0.01 poise (or 1 centipoise).
- Water viscosity at 37°C is 0.695 centipoise
- Plasma viscosity at 37°C is 1.2 centipoise with a relative viscosity of 1.7
- Blood viscosity at 37°C is 2.8-3.8 centipoise with a relative viscosity of 4-5.
Factors Affecting Blood Viscosity
-
Blood Composition Changes
- RBC mass: Increased RBCs and Hemoglobin increase viscosity. Anemia decreases viscosity. Polycythemia increases viscosity.
- Plasma proteins: Increased plasma protein increases viscosity. However, changes in plasma proteins have less effect than RBC changes.
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Cells Deformation
- Hereditary spherocytosis and sickle cell diseases increase viscosity.
-
Clotting Mechanisms
- If clotting mechanisms are stimulated platelets aggregate and interact with plasma proteins. This entraps red cells, forming clots and dramatically increasing blood viscosity.
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Temperature
- A decrease in body temperature increases blood viscosity. Blood viscosity increases 2% for each 1°C decrease.
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Shear Rate or Blood Flow Velocity Gradient
- Viscosity decreases as shear rate or blood flow increases.
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Plasma Skimming
- The concentration of RBCs decreases as blood approaches smaller blood vessels. Larger branches have higher flow rates, more RBCs, and higher hematocrits, whereas smaller branches (with lower flow rates) have less RBCs and lower hematocrits.
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Diameter of Blood Vessel (Fahraeus-Lindquist Effect)
- Viscosity decreases with decreasing vessel diameter. This effect disappears at diameters greater than 0.5 mm. In small vessels, a cell-free plasma layer forms adjacent to the vessel walls.
Blood Flow: A New Equation
-
Overview
- Cardiac output, flow, and resistance.
- Compliance and elasticity
-
Effective Perfusion Pressure
- Arterial pressure minus venous pressure.
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Pressure Gradient
- Drives blood from high pressure area to a lower pressure area
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Critical Closing Pressure
- The point at which the vessel collapses, flow ceases, and the lumen closes. For whole blood: 20mmHg; For Plasma: 5-10mmHg.
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Flow and Resistance
- Flow is inversely proportional to resistance.
- Resistance cannot be directly measured
- Total Peripheral Resistance (TPR) -Total resistance in circulatory system
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Local Resistance
- Resistance specific to local vessel conditions (varies with vessel constriction and dilation).
- Poiseuille-Hagen Formula -Flow (conductance) is directly related to the fourth power of the vessel radius, and inversely related to viscosity and vessel length.
Compliance and Elasticity
- Compliance is the ability of a vessel to expand or change volume in response to pressure changes.
- Elastance is the ability of a vessel or hollow organ to recoil toward its original dimensions.
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Compliance for Blood Vessels
- The relationship between change in volume and change in pressure is usually non-linear
- The slope of the volume-pressure curve decreases as volume increases.
- Vein compliance is greater than artery compliance at lower pressures.
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Compliance of the Ventricles
- The relationship between change in volume and change in pressure is not linear
- Laplace Law Describes the relationship between tension in a vessel wall, internal pressure, radius, and overall wall thickness.
- Vascular Distensibility -Measurement of the vessel's ability to stretch relative to changes in pressure and volume.
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Description
Test your knowledge on the dynamics of blood flow, pressure, and circulation in the human body. This quiz covers key concepts such as blood vessel movement, plasma skimming, and the effects of pressure on blood behaviors. Perfect for students studying physiology or healthcare-related fields.
