2.5 & 2.6 Flashcards
2.5. Organization of the circulatory system. Hemodynamic functions of different vessel segments in the systemic circulation. Biophysical basis of blood flow. Relationship of pressure and flow. 2.6. Measurement of arterial blood pressure. Factors influencing arterial blood pressure.
I. Organization of the circulatory system
1. How the the circulatory system organize?
Compromised of 3 systems that work together:
1. Heart (cardiovascular)
2. Pulmonary circulation: propels blood to the lungs for exchange of O2 and CO2
3. Systemic circulation: carries O2, nutrients and hormones to peripheral tissues and removes waste products (CO2)
I. Organization of the circulatory system
2. What are other functions of the circulatory system?
- Nutrient/waste transport
- Thermoregulation
- Hormone transport
- Immune function
II. Hemodynamic functions of different vessels
1. What are Hemodynamic functions of Aorta, large arteries?
- Windkessel effect of the large elastic arteries convert intermittent, pulsatile blood flow resulting from heartbeat into a steady flow
a) During the systole, high elastic content of the wall of the aorta allows it to store a great amount of blood
-> elastic potential energy stored during systole
b) In the diastole, previously stored elastic potential energy pushes the stored blood to the periphery as the aorta returns to its original shape
II. Hemodynamic functions of different vessels
2. What are Hemodynamic functions of Middle and small arteries?
- Transport blood into arterioles
- Pulse pressure↓, but still present, which can be palpated in some regions
II. Hemodynamic functions of different vessels
3. What are Hemodynamic functions of Arterioles?
- Provides the largest degree of resistance in the systemic circulation
- Their SMCs are single unit
- Pacemaker cells provide continuous vasoconstriction
- Resting tone:
+) Myogenic tone from smooth muscle
+) Sympathetic tone from sympathetic innervation
II. Hemodynamic functions of different vessels
4. What are Hemodynamic functions of Veins?
- Much higher capacitance due to lower elastic tissue content in walls
- Contain ~65% of total blood volume, so major hemodynamic functions can be considered storage
III. Relationship of pressure and flow
1. What are the 2 type of blood vessels in human (not anatomically)
1) Lung-type vessels (contains elastic fiber)
2) Kidney-type vessels (contains smooth muscle)
III. Relationship of pressure and flow
2. How does Lung-type vessels (contains elastic fiber) work?
- Works under passive mechanism
- Lung-type vessels are very compliant, so the volume increases proportionally as the pressure increases
- As the pressure (gradient) increases, the resistance within the vessel constantly decreases
-> Results from the increase in diameter/radius of the vessel due to the elastic fibers int these vessels (passive mechanism)
-> Resistance equation: when d/r increases, resistance decreases
III. Relationship of pressure and flow
3. How does Kidney-type vessels (contains smooth muscle) work?
- Works under active mechanism
- Kidney-type vessels maintain a constant blood flow within a certain range of blood pressure via autoregulation
- As the pressure increases, the resistance will also increase
-> Results from the increased tension in the vessel wall, which contains SM
1. Smooth muscle contains ‘’stretch-activated non-specific cation channels’’
2. When these channels are activated -> depolarization
3. Depolarization activates VGCC -> influx of Ca2+ -> vasoconstriction
4. Vasoconstriction will decrease the diameter / radius -> resistance equation
III. Relationship of pressure and flow
4. What are the characteristics of active reaction in blood vessels?
- Requires active reaction response of SMCs
- Bayliss effect (autoregulation): certain range of
pressure, where blood flow is constant
IV. Biophysical basis of blood flow
1A. What does Continuity equation state?
In stationary flow of blood , the volumetric flow rate (IV) at any point along the tube is constant
IV. Biophysical basis of blood flow
1B. How to use continuity equation?
- Formula: 𝐼𝑉 = 𝐴1 ∗ 𝑣1 = 𝐴2 ∗ 𝑣2 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
- Total cross-sectional area (CSA) of the vessels are inversely proportional to the volumetric flow
=> CSA is the greatest in the capillaries, hence,
the volumetric flow rate is the lowest there
IV. Biophysical basis of blood flow
2. What does Bernoulli’s Law state? How to calculate it?
- An increase in the speed of blood flow (dynamic pressure) occurs simultaneously with a decrease in hydrostatic pressure (side pressure) -> when the flow speed increases, side pressure decreases
- The blockage of a major vessel will increase the speed of blood flow, and it results in the side pressure supplying the branching vessels
IV. Biophysical basis of blood flow
3. What does Hagen-Poiseuille Law state?
The largest volumetric flow rate (IV) is achieved at the section in a circulatory system where the diameter of a vessel is the largest
=> Volumetric flow rate is proportional to the 4th power of the radius of the blood vessel
IV. Biophysical basis of blood flow - Resistance equation
4A. What are the 2 factors that determine the blood flow?
- Pressure gradient between 2 ends of the blood vessels
- Resistance provided by the vessels (to the blood flow)
IV. Biophysical basis of blood flow - Resistance equation
4B. What is the mechanism of changing blood flow?
It is changing the resistance
IV. Biophysical basis of blood flow - Resistance equation
4C. How to calculate by using resistance equation?
- Ohm’s law: pressure gradient is the voltage (U), volumetric flow rate is the current (I)
=> U=I*R -> Δp = Q * R -> Q= 1/R * Δp - Combination of the Ohm’s law and H-P-Law gives us the resistance equation:
- Most important: resistance is inversely proportional to the 4th power of the radius
IV. Biophysical basis of blood flow - Serial/ parallel resistances
5A. Characteristics of serial resistance?
- To calculate the total resistance of vessels connected continuously in series, you add up the individual resistances
- Formula: 𝑅𝑇𝑜𝑡𝑎𝑙 = 𝑅1 + 𝑅2 + 𝑅3
IV. Biophysical basis of blood flow - Serial/ parallel resistances
5B. Characteristics of Parallel resistance?
- To calculate the total resistance of vessels flowing through different organ systems, you can add up the reciprocal of the individual resistances
IV. Biophysical basis of blood flow - Serial/ parallel resistances
5C. Characteristics of Total peripheral resistance?
Total resistance that must be overcome to push the blood through the circulatory system and create flow
IV. Biophysical basis of blood flow
6B. How to use Reynold’s Number?
Important: high diameter, high velocity or low viscosity (decreased hematocrit in blood) can cause turbulence
IV. Biophysical basis of blood flow
6C. What are the diseases you can observe by using Reynold’s Number?
- Anemia: decreased hematocrit = turbulent flow
- Stenosis: small diameter of the vessel = turbulent flow
- Aneurysm: weakness of wallincreases the diameter = turbulent flow
IV. Biophysical basis of blood flow
7A. What is the definition and formula of Laplace’s Law?
- The tension within the wall of a sphere filled with a particular pressure depends on the thickness of the blood vessel wall
IV. Biophysical basis of blood flow
7B. Describe a disease you can observe by using Laplace’s Law?
Aneurysm
-> Bulging of blood vessel/GI-tract wall causes an increased lumen radius and decreased wall thickness, causing a great increase in wall tension, which may result in rupture
IV. Biophysical basis of blood flow
8A. What is Distensibility?
Ability to distend and increase its volume according to increasing transmural pressure
IV. Biophysical basis of blood flow
8B. How to measure distensibility?
- Measured in % volume change per mmHg (V0 = original volume)
- Distensibility of veins is 8x greater than distensibility of arteries
IV. Biophysical basis of blood flow
8C. Compare the Distensibility between the vein and the artery
- Distensibility of veins is 8x greater than distensibility of arteries
IV. Biophysical basis of blood flow
8D. What is Compliance?
- The slope of the tangent of any point along the pressure-volume curve
- Measure of the distensibility
IV. Biophysical basis of blood flow
8E. What are the characteristics of Compliance
- The higher the compliance of a vessel is, the more volume it can hold at a given pressure
- Arteries have a rather stable resistance despite changes in transmural pressure, therefore, they are referred to as resistance vessels
- High compliance of veins allow them to accommodate large volumes of blood with less buildup of pressure, therefore, they are referred to as capacitance vessels (C = ∆V/ ∆p)
IV. Biophysical basis of blood flow
8F. Compare the compliance between the vein and artery
Compliance of veins is 25x greater than compliance of arteries
IV. Biophysical basis of blood flow - Shear / Viscosity (Fåhræus-Lindqvist effect)
9B. Application of shear IN BLOOD VESSELS
- Near the wall, there is a layer of slow-moving blood
- In the center of the lumen, blood flows the fastest (RBC)
- The difference in velocities is the shear (shear is highest near the wall and lowest at the center)
- According to the bridge analogy. The relative amount of faster particles will decrease, and since RBC is the fastest -> hematocrit will decrease
V. Interpret this graph
- The pressure starts off high and towards the end, the pressure is about 4mmHg.
- In the aorta, the pressure is high due to the low compliance of the wall and the pressure caused by the CO.
- Little energy is lost in the large arteries, but then there is a huge decrease in pressure in the small arteries – due to the high resistance.
- Since pressure + resistance are inversely related, the pressure goes down as resistance goes up.
- In capillaries the pressure decreases even further until the blood gets to the right atrium which is a pressure of 2 – 0mmHg
VI. Measurement of arterial blood pressure
1. How is blood pressure measured?
The BP measured in the upper arm represents the pressure within the brachial artery (Differs from pressure in the aorta)
VI. Measurement of arterial blood pressure
2. What are the characteristics of Invasive measurement of BP – insertion of catheter?
- In the brachial artery, the P sys is increased while the P dia is decreased, therefore P pulse↑
VI. Measurement of arterial blood pressure
3. What are the characteristics of Non-invasive measurement of BP - sphygmomanometry?
- During sphygmomanometry, a clinician inflates the cuff to a pressure that is greater
than the Psys and then slowly releases the pressure in the cuff
Systolic pressure corresponds to the first tapping sound (usually 120mmHg)
Diastolic pressure corresponds to the muffling (dampening) of the sounds
(usually 80mmHg)
VI. Measurement of arterial blood pressure
4. What is the value of systolic pressure?
- Systolic pressure = the highest arterial pressure in cardiac cycle and is the pressure in the arteries after blood has been ejected from LV during systole.
- Systolic pressure = 120mmHg (Psys)
VI. Measurement of arterial blood pressure
5. What is the value of Diastolic pressure?
- Diastolic pressure = the lowest arterial pressure in cardiac cycle and is the pressure in the arteries during
ventricular relaxation (no ejection from LV) - Diastolic pressure = 80mmHg (Pdiastolic)
VI. Measurement of arterial blood pressure
6. What is the value of Pulse pressure?
- Pulse pressure = the difference between systolic pressure and diastolic pressure.
- Pulse pressure = 40mmHg (Ppulse)
VI. Measurement of arterial blood pressure
7. What is the value of the mean arterial pressure?
- Mean arterial pressure is the average pressure in a complete cardiac cycle
- Mean arterial pressure = 93 mmHg
=> If the heart rate increases, both diastole and systole time length decrease but it is more effective for diastole. - E.g., if the HR is 120 bpm, time length of diastole and systole are roughly equal to each other thus increases the mean arterial pressure.
VII. Factors influencing arterial blood pressure
1. What are the Factors influencing arterial blood pressure?
- Physical parameters
1) Blood volume: the greater the blood volume, the higher the blood pressure
-> Greater SV results in an increased CO
2) Compliance (V/P): high compliance associated to a low pressure, as the blood vessel expands upon receiving of a great volume of blood and vice versa - Physiological parameters
1) Cardiac output (SV*HR): volume which enters the system
2) TPR: how blood can leave the arterial system
VII. Factors influencing arterial blood pressure
3. How can Compliance (V/P) influence blood pressure?
Aging results in loss of elastic fibers in the vascular walls
-> compliance decreases
-> affecting pressure
Psys increases, Pdia decreases = high Ppulse
VII. Factors influencing arterial blood pressure
4. How can Increasing Cardiac output (SV*HR) influence blood pressure?
An increase in CO results in an overall pressure increase, but a larger increase in Psys than Pdia
-> Ppulse also changes (increases)
VII. Factors influencing arterial blood pressure
5. How can increasing total peripheral resistance (TPR) influence blood pressure?
Changes Psys and Pdia equally, so
no change in Ppulse.
In older people, ΔPsys > ΔPdia
VII. Factors influencing arterial blood pressure
7. How can GRAVITATION influence blood pressure?
- Affects BP depending on body position
- 1cmH2O = 0,7mmHg
- Standing: pressure is higher in lower limbs when standing
- Lying down: both arteries and veins affected equally, pressure difference between them is unchanged
