Chapter 5- Part 1 Flashcards
What are the two basic functions of the vascular system?
Distribution and exchange
Describe the anatomical vascular structures.
Aorta-lg arteries-sm arteries-arterioles-capillaries-venules-veins-vena cava
What is the primary function of the aorta, large arteries, small arteries, arterioles, capillaries, venules, veins, and the vena cava?
Aorta-pulse dampening and distribution
Large Arteries-distribution Small Arteries-distribution and resistance
Arterioles-resistance
Capillaries-exchange
Venules-exchange and collection and capacitance
Veins-capacitance
Vena Cava-collection
Based on the vessel diameter, what would differentiate small arteries from arterioles?
No clear demarcation between small arteries and arterioles exist
What are the primary resistance vessels?
Small arteries and arterioles
Describe the structure and function of resistance vessels – innervation, receptors, response to
vasoactive signals?
Innervation-Highly innervated by autonomic nerves
Receptors-Richly endowed with receptors that bind circulating hormones
Response to vasoactive signals-Alter vessel diameter
At what size (vessel diameter) do arterioles lose their smooth muscle?
<10 micrometer
Anatomically speaking, what is a capillary?
Composed of only endothelial cells and a basement membrane
What are the smallest vessels in terms of diameter?
Capillaries
What category of vessels has the largest cross-sectional area within the circulation?
Capillaries
What is the blood flow velocity through the aorta?
~50 cm/s
What is the total blood flow through the aorta?
IDK
What is the blood flow velocity through all of the capillaries?
~0.05 cm/s
What is the total blood flow through the capillaries?
IDK
What is the relationship between mean velocity and cross-sectional area?
Mean velocity is inversely proportional to the cross-sectional area. V=F/A
What equation explains this relationship?
V=F/A
What vessels are the primary exchange vessels in the body?
Capillaries
What are postcapillary venules?
Devoid of smooth muscle which serve as exchange vessels for fluid and macromolecules due to high permeability
Describe the anatomy of venules and veins.
Smooth muscle reappears and allows for constricting/dilation
What is meant by the term “capacitance vessels”?
The site where most of the blood volume is found and regional blood volume is regulated
What does venous constriction do to venous volume and venous pressure?
Decreases venous blood volume and increases venous pressure
How could this affect cardiac output?
Alter cardiac output by affecting RA pressure and vent. preload
What are the final venous vessels?
IVC and SVC
What is the mean blood pressure in the aorta, arteries, arterioles, capillaries, venules, veins, and vena cava?
Aorta-95 Arteries-90 Arterioles-55 Capillaries-25 Venules-15 Veins-10 Vena Cava-5
Why does pressure progressively decrease as the blood gets further away from the heart?
Energy is lost as heat owing to friction within the moving blood and between the blood and the vessel wall
What equation can be used to describe the pressure drop that occurs?
dP=FxR
Change in Pressure= Flow times resistance
Why does mean blood pressure not fall much as the blood flows down the aorta and through large distributing arteries?
These vessels have a low resistance relative to their flow
Why is there a large fall in mean blood pressure as blood flows through the small arteries and arterioles?
These vessels have a high resistance relative to their flow
What percentage of the pressure drop across the entire cardiovascular system occurs within the resistance vessels?
Approximately 50-70%
Why is it important that capillary pressure remains relatively low?
Control fluid leaking through the vessels causing tissue edema
What is the percent of blood volume in the aorta, arteries, arterioles, capillaries, venules, veins, and vena cava?
Aorta-5 Arteries-10 Arterioles-5 Capillaries-5 Venules-25 Veins-50 Vena Cava-5
What factors determine the relative blood volume between the arterial and venous sides of the circulation?
Total blood volume, intravascular pressures, and vascular compliance
Draw a curve representing the pressure pulse in the aorta.
A
What would the variables and values be for the both the x and y axes?
X-Time
Y-Pressure
On this curve identify systolic pressure, diastolic pressure, mean pressure, pulse pressure, and the dicrotic notch.
P systolic is the peak, Incisura is the notch, followed by the dicrotic wave
The P diastolic is at the low point with the P mean being in between
What is another name for the dicrotic notch?
Incisura
What equation is used to calculate pulse pressure?
Psys-Pdias
Which of these pressures is the primary pressure that drives blood flow to the organs?
Mean arterial pressure
Is mean blood pressure the geometric mean or the arithmetic average of systolic and diastolic pressure?
Geometric mean
What equation can be used to estimate mean arterial pressure from systolic and diastolic pressures?
MAP= Pdias + 1/3(Psys-Pdias)
At higher heart rates, is mean blood pressure closer to the geometric mean or the arithmetic average of systolic and diastolic pressure? Why?
Arithmetic avg, because the shape of the arterial pressure pulse changes as the period of diastole shortens more than does systole
Give an approximate value for mean arterial pressure in infant children and older adults.
MAP(Infant children)= 70 mmHg
MAP(Older adults)= 100 mmHg
What is the effect of aging on systolic, diastolic, and mean pressure?
Systolic pressure generally rises more than diastolic pressure
What are the differences in mean pressure between men and women?
Women have slightly lower MAP
What are normal values for systolic, diastolic, and mean pressures?
<120 mmHg Systolic
<80 mmHg Diastolic
<95 mmHg MAP
What variables are used to calculate mean arterial pressure?
Cardiac Output (CO), Systemic Vascular Resistance (SVR), and Central Venous Pressure (CVP)
What is another equation (not the equation from question #40) that can be used to calculate mean arterial blood pressure?
MAP=(CO x SVR) +CVP
In the textbook, how is equation 5-3 related to equation 5-1?
5-1: dP=FxR 5-3: MAP=(CO x SVR) +CVP dP=MAP-CVP F=CO R=SVR
If cardiac output and systemic vascular resistance change reciprocally and proportionately, what will happen to mean arterial pressure?
MAP will not change
Draw a figure that shows the relationship between cardiac output (independent variable) and mean arterial pressure (dependent variable).
CO on X
MAP on Y
How would this curve change with an increase or a decrease in systemic vascular resistance?
Increasing SVR increases MAP at any given CO and decreasing SVR decreases SVR decreases MAP at a given CO
How are cardiac output, systemic vascular resistance, and venous pressure interdependent?
Changing one variable can change each of the other variables
What happens to systolic and diastolic pressures as blood moves away from the heart?
Systolic rises and diastolic falls
What happens to mean arterial pressure as the pressure pulse travels down the distributing arteries and why does this happen?
MAP declines as the pressure pulse travels down the distributing arteries. This happens because of resistance of the arteries
What two variables determine compliance?
Volume and pressure
What equation is used to measure compliance?
C=dV/dP or dV=CxdP
How would you compare a highly compliant vessel with a “stiffer” vessel?
A highly compliant vessel will display a relatively small increase in pressure for a given increase in volume while a less compliant vessel will display a relatively large increase in pressure for a given increase in volume
What anatomical characteristics affect compliance, and how do they do it?
The relative proportion of elastin fibers vs. smooth muscle and collagen in the vessel wall
Elastin offers the least resistance to stretch while collagen offers the most resistance to stretch
What would happen to pulse pressure if the aorta were a hard, rigid tube?
If the aorta were a rigid tube, the pulse pressure would be very high with each ventricular ejection
Describe how aortic compliance changes this.
The walls of the aorta expand to accommodate the increase in blood volume
How does pulse pressure change with a highly compliant aorta versus a less compliant aorta?
The less compliant the greater the pressure change at any given change in aortic volume
What might you expect pulse pressure to be in an elderly individual or a health adult at rest?
Elderly- 60 mmHg or more
Younger Adult- 40-45 mmHg
Draw a curve showing the relationship between aortic pressure and aortic volume with normal aortic compliance and a mean arterial pressure of 90 mmHg.
A
On this curve, highlight a normal dV and dP.
Thin dV and dP
Draw this curve with an increase in stroke volume.
Increases both dV and dP, slightly increased slope
Draw this curve with an increase in mean aortic pressure
Increased dP, slightly increased slope
How would this curve change with a decrease in compliance?
Increased dP, lower slop
Why is there no single value for aortic compliance?
Because the relationship between volume and pressure is not linear
What is the slope like at higher pressures and volumes?
Decreased
How is the pulse pressure different at elevated mean arterial pressures compared to low mean arterial pressures?
Reduced compliance results in an increase in pulse pressure at a given stroke volume
What are some factors that could change stroke volume – which would in turn affect pulse pressure?
Vent. Preload, afterload and inotropy as well as heart rate
What are some factors that could change aortic compliance – which would in turn affect pulse pressure?
Age, arterioschlerosis, hypertension
Are chronic long-term increases in pulse pressure due to changes in stroke volume or compliance?
Decreased aortic compliance
Define the term hemodynamics.
The physical factors governing blood flow within the circulatory system
What equation is used to determine blood flow through an organ?
F=dP/R
F is flow, dP is the pressure gradient, R is the resistance
How can this equation be used to measure flow through an individual blood vessel?
The pressure gradient is the pressure difference between two defined points along the vessel
What is the primary factor determining blood flow through an organ?
Changes in resistance due to arterial and venous pressures normally being contained to a specific range
What are the three factors that determine the resistance of blood flow?
Vessel length, blood viscosity, and resistance to blood flow
Describe how the length of the vessel contributes to resistance to blood flow.
Resistance is directly proportional to the vessel length
escribe how blood viscosity contributes to resistance to blood flow.
Viscosity is related to friction generated by interactions between fluid molecules in the plasma and suspended formed substances as the blood is flowing. Viscosity also takes into account the friction generated between the blood and the lining of the vessel
At normal body temperature, how does the viscosity of plasma compare to water?
1.8 times viscosity of water
At normal body temperature, how does the viscosity of whole blood compare to water?
3-4 times viscosity of water
What does an increase in hematocrit do to blood viscosity?
Blood viscosity approximately doubles if hematocrit goes from 40 to 60%
What does an increase in blood temperature do to blood viscosity?
Decreasing blood temp increases viscosity by about 2% per degree centigrade
What does a decrease in blood flow rate do to blood viscosity?
Increases blood viscosity
Of the three independent variables used in the equation to quantify resistance, which one is the most important in determining blood flow?
Vessel radius is the most important in determining blood flow
What is the relationship between vessel radius and resistance?
Inversely related, therefore an increase in radius reduces resistance
What will a twofold increase in vessel radius do to vessel resistance?
Decreases resistance 16-fold
If the equations for resistance and flow/pressure/resistance are combined, what is the resulting equation?
F dP x r4/n x L
Who first described this relationship?
Poiseuille
What assumptions are made when considering this relationship?
The vessels are long, straight, rigid tubes
Blood behaves as a Newtonian fluid in which viscosity is constant and independent of flow
Blood is flowing under steady laminar flow conditions
Draw a graph describing the relationship between relative radius (independent variable) and relative flow (dependent variable).
A
In this graph, what would happen to flow if the relative radius were decreased by one-half (i.e., a
change from 1.0 to 0.5)?
decreased 16-fold
How would you explain this decrease in blood flow?
Very small changes in vessel radius can have a profound effect on flow
Define and describe laminar blood flow.
The normal condition for blood flow in most blood vessels which is characterized by concentric layers of blood moving down the length of a blood vessel
What is the functional advantage of laminar blood flow?
Helps minimize energy loss in the flowing blood caused by viscous interactions between the adjacent layers and the wall of the blood vessel
Define and describe turbulent blood flow.
When laminar flow becomes disrupted
Where might you see turbulent blood flow?
Turbulence is found distal to stenotic (narrowed) heart valves or arterial vessels, at large artery branch points, and in the ascending aorta at high cardiac ejection velocities
How does turbulence influence the pressure drop across the vessel?
A greater perfusion pressure is required to propel the blood at a given flow rate when turbulence is present
If blood flow is increased twofold across a stenotic arterial segment, what would you expect to happen to the pressure drop across the stenosis?
May increase threefold or fourfold and the turbulence is enhanced
If a single vessel in the kidney were constricted by 50%, what would happen to the resistance in that single vessel?
It would increase 16-fold
If a single vessel in the kidney were constricted by 50%, what would happen to the resistance in the entire organ?
It would not increase the overall resistance in the entire organ by that much because it is only a small part of the overall resistance network
What affect do parallel vessels have on total vascular resistance?
Parallel vessels decrease total vascular resistance
What equation would be used to calculate the total resistance of three parallel resistances?
1/Rt=1/R1+1/R2+1/R3
Is the total resistance of a network of parallel resistances less than, equal to, or greater than the resistance of the single lowest resistance?
Less than
If resistance 1 (R1) = 5, R2 = 10, and R3 = 20 were in parallel, what would the total resistance be?
2.86
What is the relevance of this observation?
It is a value which is less than the lowest individual resistance
When many parallel vessels exist, what effect does changing the resistance in a small number of these vessels have on total resistance?
Changing the resistance in a small number of these vessels has a little effect on total resistance
Describe the series and the parallel arrangement of vessels in a single organ.
Series: All of the blood that flows through the artery likewise flows through each of the other vascular segments
Parallel: Many capillaries can exist in a capillary bed resulting in the spreading of the fluid throughout many vessels
What equation would be used to calculate the total resistance of five resistances in series (use
arteries, arterioles, capillaries, venules, veins as segments)?
Rt=RA+Ra+RC+Rv+RV
Using this example, calculate total resistance using these values: RA =1,Ra =70,Rc =20,Rv =8, RV = 1.
Rt=100
What would happen to total resistance if RA were increased fourfold to a value of 4?
Rt=103, increasing by 3%
What would happen to total resistance if Ra were increased fourfold to a value of 280?
Rt=310, increasing by 210%
What is the effect of a change in large artery resistance on total resistance?
Change in large artery resistance have relatively little effect on total resistance
What is the effect of a change in small artery/arteriole resistance on total resistance?
Change in small artery resistance have a large effect on total resistance
Define critical stenosis.
The radius of a large, distributing artery must be decreased by more than 60% to have a significant effect on the organ blood flow
