Cardiovascular Physiology (Part 1) Flashcards
What is the primary function of the cardiovascular system?
to deliver blood to the tissues, providing essential nutrients to the cells for metabolism and removing waste products from the cells
Do arteries or veins contain the majority of the blood volume?
The veins contain the largest percentage of blood volume
Where does the exchange of nutrients, wastes, and fluid occur?
across the capillary walls
What some other functions of the cardiovascular system?
- participates in regulation of arterial BP
- delivers regulatory hormones from the endocrine glands to their sits of action in target tissues
- participates in regulation of body temperature
- involved in the homeostatic adjustments to altered physiologic states such as hemorrhage, exercise, and changes in posture
The left heart and the systemic arteries, capillaries, and veins are collectively called the _____ circulation
systemic
The right heart and the systemic arteries, capillaries, and veins are collectively called the _____ circulation
pulmonary
The ___ ventricle pumps blood to all organs of the body except the lungs
left
The ___ ventricle pumps blood to the lungs
right
The two sides of the heart operate in series, what does this mean?
Blood is pumped sequentially from the left heart to the systemic circulation, to the right heart, to the pulmonary circulation, and then back to the left heart
The rate at which blood is pumped from either ventricle is called what?
cardiac output
Are the cardiac outputs equal between the right and left ventricles? Why or why not?
The cardiac output of the left ventricle equals the cardiac output of the right ventricle in the steady state because the 2 sides of the heart operate in series
The rate at which blood is returned to the atria from the veins is called what?
venous return
Does return to the left heart equal that to the left heart? Why or why not?
Yes, because the 2 sides of the heart operate in series
In the steady state, cardiac output from the heart _____ venous return to the heart
equals
What are the functions of the blood vessels
- serve as closed system of passive conduits, delivering blood to and from the tissues where nutrients and wastes are exchanged.
- participate actively in the regulation of blood flow to the organ
Describe the steps involved in one complete circuit through the cardiovascular system
1) oxygenated blood fills the left ventricle
2) blood is ejected from the left ventricle
3) cardiac output is distributed among various organs
4) blood flow from the organs is collected in veins
5) venous return to the right atrium
6) mixed return to the right atrium
7) blood is ejected from the right ventricle into the pulmonary artery
8) blood flow from the lungs is returned to the heart via the pulmonary vein
Blood that has been oxygenated in the lungs returns to the left atrium via what?
the pulmonary vein
Blood that flows from the left atrium to the left ventricle goes through what valve?
the mitral valve
Blood leaves the left ventricle through what valve?
the aortic (semilunar) valve
What percentage of cardiac output is delivered to the brain?
15%
What percentage of cardiac output is delivered to the heart?
5%
What percentage of cardiac output is delivered to the kidneys?
25%
What percentage of cardiac output is delivered to the GI tract?
25%
What percentage of cardiac output is delivered to skeletal muscle?
25%
What percentage of cardiac output is delivered to the skin?
5%
What are the 3 major mechanisms for achieving a change in blood flow to an organ system?
- CO remains constant, but the blood flow is redistributed among the organ systems by selective alteration of arteriolar resistance
- CO increases or decreases, but the percentage distribution of blood flow among the organ systems is kept constant
- both CO and the percentage of blood flow are altered
When are both CO and the percentage of blood flow are altered?
In response to strenuous exercise: blood flow to skeletal muscle increases to meet the increase metabolic demand by a combination of increased CO and increased percentage distribution to skeletal muscle
What is the largest vein?
the vena cava
Is pressure higher in the vena cava or in the right atrium? Explain the importance of this
Pressure is higher in the vena cava which allows for blood to flow into the right atrium
In the steady state does venous return to the right atrium equal cardiac output from the left ventricle?
Yes
Mixed blood traveling from the right atrium to the right ventricle travels through what valve?
the tricuspid valve
Describe the path blood takes once it is ejected from the right ventricle
It is ejected through the pulmonic valve into the pulmonary artery, which carries blood to the lungs.
Describe the gas exchange that occurs in the lungs
Oxygen is added to the blood from alveolar gas, and carbon dioxide is removed from the blood and added to the alveolar gas
What does hemodynamics refer to?
the principles that govern blood flow in the cardiovascular system
What are blood vessels?
The conduits through which blood is carried from the heart to the tissues and from the tissues back to the heart
Describe the direction of blood flow through the vascular bed
artery –> arteriole –> capillaries –> venule –> vein
Which type of blood vessel has the largest total cross-sectional area
the capillaries
Which type of blood vessel has the largest percentage of the blood volume contained in them?
veins
What is the function of the arteries?
to deliver oxygenated blood to the organs
Are arteries thick or thin?
thick
What are arteries made of?
extensive amounts of elastic tissue, smooth muscle, and connective tissue
The volume of blood contained in the arteries is called what?
the stressed volume
What are arterioles?
the smallest branches of the arteries
Which blood vessels are the site of highest resistance to blood flow?
arterioles
What are arterioles composed of?
smooth muscle
Describe smooth muscle contraction in arterioles
it is tonically active (always contracted)
What is the smooth muscle in arterioles innervated by?
sympathetic adrenergic nerve fibers
What type of receptors are found on the arterioles of vascular beds (skin and splanchnic vasculature)?
alpha1-adrenergic receptors
What happens when alpha1-adrenergic receptors are activated?
They cause constriction of the vascular smooth muscle with produces a decrease in the diameter of the arteriole, which increases its resistance to blood flow
What type of receptors are found in the arterioles of skeletal muscle?
beta2-adrenergic receptors
What happens when beta2-adrenergic receptors are activated?
They cause relaxation of the vascular smooth muscle, which increases the diameter and decreases the resistance of these arterioles to blood flow
Describe the structure of capillaries
They are thin-walled structures lined with a single layer of endothelial cells surrounded by a basal lamina
How do lipid-soluble substances cross the capillary wall?
They dissolve in and diffuse across the endothelial cell membranes
How do water-soluble substances cross the capillary wall?
They either cross through water-filled clefts between the endothelial cells or through large pores in the walls of some capillaries
Are all capillaries perfused with blood at all times?
No, there is selective perfusion of capillary beds depending on the metabolic needs of the tissues
What are venules and veins made of?
A modest amount of elastic tissue, smooth muscle, and connective tissue
Veins have a large capacitance in contrast to arteries, what does this main?
They have a large capacity to hold blood
The volume of blood constrained in the veins is called what?
unstressed volumes
Increase in sympathetic activity to the veins causes what?
constriction of the veins, which reduces their capacitance, and therefore reduces the unstressed volume
What is the velocity of blood flow?
The rate of displacement of blood per unit time
What are the 2 factors in which blood velocity depend on?
flow and cross-sectional area
velocity (v) = flow (Q) / cross-sectional area (A)
As vessel diameter increases, velocity of flow _____.
decreases
Where is the velocity of blood flow the highest and where is it the lowest?
highest in the aorta and lowest in the capillaries
Why is low velocity of blood flow advantageous in capillaries?
It maximizes the time for exchange across the capillary wall
Blood flow through a blood vessel or a series of blood vessels is determined by what 2 factors?
- the pressure difference between the 2 ends of the vessel
- the resistance of the vessel to blood flow
Flow (Q) = pressure difference (P) / resistance (R)
The pressure _____ is the driving force for blood flow, and the _____ is an impediment to flow
difference
resistance
Blood flow is always from ___ to ___ pressure
high to low pressure
Increasing resistance (vasoconstriction) _____ blood flow, and decreasing resistance (vasodilation) _____ blood flow
decreases
increases
What is total peripheral resistance?
the resistance of the entire systemic vasculature
What is total peripheral resistance aka?
systemic vascular resistance
What are 2 other factors in which resistance to flow depend on?
- blood viscosity
- length of the vessel
The factors that determine the resistance of a blood vessel to blood flow are expressed by what equation?
Poiseuille Equation
What is the Poiseuille equation?
R=8ηl / πr ^4
R: resistance
η: viscosity of blood
l: length of blood vessel
r^4: radius of blood vessel raised to the fourth power
As viscosity increases the resistance to blood flow _____.
increases
As the length of the blood vessel increases the resistance to blood flow _____.
increases
When the radius of a blood vessel decreases, its resistance _____.
increases to the magnitude of the fourth power
If the radius of a blood vessel decreases by one half, what does the resistance to blood flow do?
It increases by 16-fold (2^4)
What are the 2 ways in which resistances in the cardiovascular system can be arranged?
In series or in parallel
Series resistance is illustrated by what?
the arrangement of blood vessels within a given organ
What is the total resistance of a system arranged in series equal to?
the sum of the individual resistances
R(total) = R(artery) + R(arterioles) + R(capillaries) + R(vanuels) + R(veins)
Of the various resistances in series, which resistance is by far the greatest?
arterioles
When resistances are arranged in series, the total flow through each level of the system ____.
is the same
Although total flow is constant at each level in the series, what happens to the pressure?
It decreases progressively as blood flows through each sequential component
Where does the greatest decrease in pressure occur in a series resistance? Why?
In arterioles, because they contribute the largest portion of the resistance
Parallel resistance is illustrated by what?
the distribution of blood flow among the various major arteries off the aorta
The total resistance in a parallel arrangement is ___ than any of the individual resistances
less
When blood flow is distributed through a set of parallel resistances, the flow though each organ is what?
just a fraction of the total blood flow
What are the effects of a system arranged in parallel?
- there is no loss of pressure in major arteries
- mean pressure in each major artery will be approximately the same as mean pressure in the aorta
What does adding a resistance to a parallel circuit cause?
Total resistance to decrease
If the resistance of one of the individual vessels in a parallel arrangement increases, then the total resistance _____.
increases
Ideally blood flow in the cardiovascular system is laminar, what does this mean?
It is streamlined
In laminar flow where is the velocity of blood flow the highest and where is it the lowest?
It is highest in the center of the vessel and lowest towards the vessel walls (develops a parabolic profile)
Why does the parabolic profile develop?
Because the layer of blood next to the vessel wall adheres to the wall and does not move essentially, and the successive layers slip past the motionless layer a moves a bit faster, with less adherence to adjacent layers
The velocity of flow at the vessel wall is ____ and the velocity at the center of the stream is ______.
zero
maximal
What happens to blood flow when an irregularity occurs in a blood vessel?
The laminar stream is disrupted, and blood flow may become turbulent and more energy is required to drive the blood
Turbulent flow is often accompanied by what?
audible vibrations called murmurs
What is the Reynolds number?
a dimensionless number that is used to predict whether blood flow will be laminar or turbulent
What are the factors that the Reynolds number considers?
- diameter of the blood vessel
- mean velocity of flow
- viscosity of the blood
NR=ρdv / η
ρ: density of blood
d: diameter of blood vessel
v: velocity of blood flow
η: viscosity of blood
If Reynolds number is less than _____ blood flow will be laminar. If it is greater than this number it will be turbulent
2000
Decreases in blood viscosity cause an ____ in Reynolds number
increase
Narrowing a blood vessel, which produces an increase in velocity of blood flow, causes an ____ in Reynolds number
increase
What are the 2 common clinical situations that illustrate the application of Reynolds number in predicting turbulence?
anemia and thrombi
What is anemia?
A disease associated with a decreased hematocrit and, because of turbulent blood flow, causes functional murmurs
Reynolds number is _____ in anemia due to what 2 things?
increased
Decreased blood viscosity and increased velocity of blood flow
What are thrombi?
blood clots in the lumen of a vessel
Reynolds number is _____ in patients with thrombi due to what?
increased
narrowing of blood vessel diameter, which causes an increase in blood velocity
When does shear occur?
When adjacent layers of blood travel at different velocities
Where is shear highest and where is it lowest?
It is highest at the blood vessel wall and lowest at the center of the blood vessel
What are the consequences of shear?
It breaks up aggregate of RBCs and decreases blood viscosity
At the vessel wall shear rate is highest and RBC aggregation and viscosity are _____.
lowest
What does the compliance or capacitance of a blood vessel describe?
the volume of blood the vessel can hold at a given pressure
What are the 2 variables of compliance?
- volume
- pressure
C = V/P
The higher the compliance of a vessel, the ____ volume it can hold at a given pressure
more
The veins are the ____ compliant and contain the unstressed volume
most
large volume under low pressure
The arteries are the ____ compliant and contain the stressed volume
least
low volume under high pressure
What does changes in compliance of the veins cause?
redistribution of blood between veins and arteries (i.e. blood shifts between the unstressed and stressed volumes)
What happens if the compliance of the veins decreases due to vasoconstriction?
There is a decrease in the volume the veins can hold and consequently there is a shift of blood from the veins to the arteries causing unstressed volume to decrease and stressed volume to increase
What happens if the compliance of the veins increases due to vasodilation?
There is an increase in the volume the veins can hold and consequently there is a shift of blood from the arteries to the veins causing stressed volume to decrease and unstressed volume to increase
What is the effect of aging on compliance of the arteries?
The walls become stiffer and less compliant
Describe the differences in blood pressure between the various blood vessels
The aorta and large arteries have the highest BP, followed by the arterioles, then the capillaries, veins, etc.
Where is BP the lowest?
in the right atrium
Where does the largest blood pressure decrease occur?
In the arterioles, due to the high resistance to flow
What are the 2 reasons why blood pressure decreases further in the capillaries?
- frictional resistance to flow
- filtration of fluid out of the capillaries
Why does blood pressure decrease as blood flows through the vasculature?
because energy is consumed in overcoming the frictional resistances
_____ pressure is the lowest arterial pressure measured during a cardiac cycle and is the pressure in the artery during ventricular relaxation when no blood is being ejected from the left ventricle
Diastolic
_____ pressure is the highest arterial pressure measured during a cardiac cycle and is the pressure in the artery after blood has been ejected from the left ventricle during systole
Systolic
When does the dicrotic notch (incisura) occur?
When the aortic valve closes
What does the dicrotic notch cause?
A brief period of retrograde flow from the aorta back toward the aortic valve which briefly decreases the aortic pressure below the systolic pressure
What is pulse pressure?
The difference between systolic and diastolic pressure
What does the magnitude of the pulse pressure reflect?
Stroke volume
What is mean arterial pressure?
the average pressure in a complete cardiac cycle
How is mean arterial pressure calculated?
Mean arterial pressure = diastolic pressure + 1/3 pulse pressure
Are systolic pressure and pulse pressure greater in large arteries or in the aorta? Explain…
In large arteries because following ejection of blood from the left ventricle the pressure wave travels at a higher velocity than the blood itself travels, augmenting the downstream pressure
Why is there a dampening and loss of pulse pressure as blood travels through the circuit?
1) the resistance of the blood vessels (particularly the arterioles) makes it difficult to transmit the pulse pressure
2) the compliance of the blood vessels (particularly the veins) damps the pulse pressure because they are so compliant
What happens to systolic pressure, pulse pressure, and mean pressure in arteriosclerosis?
Plaques deposited in the arterial walls decrease the diameter of the arteries which makes them stiffer and less compliant. This causes an increase in systolic pressure, pulse pressure, and mean pressure.
What happens to systolic pressure, pulse pressure, and mean pressure in aortic stenosis?
A narrowing of the aortic valve decreases systolic pressure, pulse pressure, and mean pressure
What happens to systolic pressure, pulse pressure, and mean pressure in aortic regurgitation?
When the aortic valve is incompetent retrograde occurs which decreases systolic pressure, pulse pressure, and mean pressure
Which has a lower pressure, pulmonary or systemic vasculature?
Pulmonary vasculature is much lower because resistance is much lower in order to achieve the same flow
