CVS 6 Blood Flow Regulation
Summary
TLDRThis educational video explores the cardiovascular system's blood distribution, focusing on factors affecting blood flow, such as pressure differences, resistance, and vessel characteristics. It explains how exercise influences blood flow through local vasodilation and the autonomic nervous system's role in regulating blood vessel constriction and dilation. The script also delves into cardiac output, the Frank-Starling law, and the body's oxygen needs, highlighting the heart's response to increased metabolic demands.
Takeaways
- đ The body regulates blood distribution based on pressure differences and resistance, with resistance varying by vessel length and diameter.
- đ Flow, pressure, and resistance are interrelated, as described by the formula: Flow = Pressure / Resistance.
- đ Poiseuille's Law states that flow is directly proportional to the pressure gradient and the fourth power of the vessel radius, inversely proportional to the vessel length and fluid viscosity.
- đ± Vessel radius is the most influential factor in blood flow, with small changes in diameter having significant effects on flow.
- đââïž During exercise, the body rapidly adjusts blood flow to meet increased energy demands, with local arterial dilation and neural signals affecting vein stiffness.
- đ At rest, the kidneys receive a large portion of the cardiac output, but this significantly decreases during intense exercise due to regional blood flow adjustments.
- đ Local vasodilation in skeletal and cardiac muscle is triggered by decreased tissue oxygen, increased temperature, and other metabolic byproducts.
- đ§ The autonomic nervous system, including sympathetic and parasympathetic branches, centrally regulates blood vessel dilation and constriction.
- đ Cardiac output is calculated by multiplying heart rate by stroke volume, reflecting the heart's pumping efficiency.
- đ The Fick Principle links cardiac output to oxygen uptake and the oxygen content difference between arterial and venous blood, providing a complex but insightful measure.
- đ The Frank-Starling Law of the Heart explains that stroke volume increases with the volume of blood filling the heart, optimizing muscle fiber stretch and cross-bridge formation.
Q & A
How does the body determine where the blood gets distributed within the body?
-The body determines blood distribution through factors that affect blood flow, such as pressure differences, resistance, and the body's metabolic demands. Resistance to blood flow is influenced by the vessel's length, diameter, and blood viscosity, with the vessel radius being the most crucial factor.
What is the basic relationship between flow, pressure, and resistance in blood vessels?
-The basic relationship is described by the formula: flow equals pressure divided by resistance. This shows that the flow of blood through a vessel depends on the pressure difference and the resistance of the vessel.
What is Poiseuille's law and how does it relate to blood flow?
-Poiseuille's law, named after French physician Jean Leonard Marie Poiseuille, describes the relationship between flow, pressure gradient, vessel radius, vessel length, and fluid viscosity. It states that flow is equal to the pressure gradient multiplied by the vessel radius to the power of four, divided by the vessel length and fluid viscosity.
How does the body adjust blood flow during exercise?
-During exercise, the body adjusts blood flow rapidly to meet increased energy demands. Local metabolic conditions and nerves cause the smooth muscle in arterial walls to change their diameter, while neural signals make veins stiffer, pushing blood from peripheral veins into central circulation. More blood flows to active muscles due to local arterial dilation, while other vessels constrict to reduce blood flow to less critical areas.
What is the significance of the kidneys' blood flow during rest and exercise?
-At rest, the kidneys receive about 20% of the total cardiac output, but during intense exercise, this drops to just 1%. This adjustment helps redirect blood flow to more active muscles and other critical areas during physical activity.
How does local vasodilation in skeletal and cardiac muscle affect blood flow?
-Local vasodilation in skeletal and cardiac muscle is triggered by a decrease in tissue oxygen, increased temperature, carbon dioxide, acidic acidity, adenosine, nitric oxide, and potassium ions. This dilation increases blood flow, improving gas and nutrient exchange between blood and muscle fibers.
What role does the autonomic nervous system play in regulating blood vessel dilation and constriction?
-The autonomic nervous system, through its sympathetic and parasympathetic branches, centrally regulates blood vessel dilation and constriction. Sympathetic nerves can release norepinephrine to constrict blood vessels or acetylcholine to dilate them, maintaining a state of vasomotor tone.
How does the Frank-Starling law of the heart relate to cardiac output and stroke volume?
-The Frank-Starling law states that the heart's stroke volume increases in response to an increase in the volume of blood filling the heart. This relationship is crucial in adjusting cardiac output to meet the body's metabolic demands.
What is the ejection fraction and why is it important in assessing cardiovascular health?
-The ejection fraction is the fraction of blood pumped from the left ventricle relative to its end-diastolic volume. It is used to assess ventricular function and predict cardiovascular health outcomes, with healthy individuals typically having an ejection fraction between 50 and 70%.
How does the distribution of cardiac output change during physical activity?
-During physical activity, the distribution of cardiac output changes to prioritize blood flow to active muscles and other critical areas. Blood flow to the liver, kidneys, and muscles increases, while other tissues may receive less blood to meet the higher metabolic demands of the body.
Outlines
đ Blood Flow and Distribution in the Cardiovascular System
This paragraph discusses the factors that determine how blood is distributed within the body. It explains that blood flow through a vessel depends on pressure differences and resistance, which varies with the vessel's length and diameter. The relationship between flow, pressure, and resistance is outlined, with resistance being influenced by blood viscosity, vessel length, and vessel radius. The Poiseuille's law is introduced, emphasizing the importance of vessel radius in affecting flow. The paragraph also highlights how the body adjusts blood flow during exercise, with local metabolic conditions and neural signals causing changes in vessel diameter, and how regional blood flow is adjusted, such as in the kidneys, to meet the body's needs.
đââïž Balancing Venous Return and Cardiac Output During Exercise
This paragraph delves into the importance of balancing venous return with cardiac output, especially during upright physical activity where gravity affects blood flow. It explains the basic formula for cardiac output, which is related to heart rate and stroke volume. The paragraph also discusses various methods to assess cardiac output, including the Fick principle, which connects cardiac output to oxygen uptake and the difference in oxygen content between arterial and venous blood. The Frank-Starling law of the heart is introduced, describing how stroke volume increases in response to an increase in the volume of blood filling the heart. The concept of preload and how it affects ventricular filling and stroke volume is also explored.
đ„ Clinical Assessment of Cardiac Function and Blood Flow
This paragraph focuses on the clinical assessment of cardiac function and blood flow. It discusses the ejection fraction, which is used to evaluate ventricular function and predict cardiovascular health outcomes. The ejection fraction is defined as the fraction of blood pumped from the left ventricle relative to its end-diastolic volume. The paragraph also explains the influence of preload and afterload on stroke volume, using volume-pressure curves to illustrate these concepts. The effects of physical activity on the distribution of cardiac output and the importance of maintaining adequate blood supply to critical organs like the heart and brain are highlighted. Additionally, the paragraph discusses the oxygen-carrying capacity of blood and how it varies with physical activity.
đĄïž Oxygen Utilization and Reserve in the Cardiovascular System
The final paragraph addresses the oxygen utilization and reserve in the cardiovascular system. It explains that at rest, the body has a significant reserve of oxygen, which is indicated by the arterial-venous oxygen difference (a-vO2 difference). The paragraph highlights that this reserve is crucial for meeting sudden physical demands. It also discusses the oxygen-carrying capacity of arterial blood and how trained and untrained adults circulate about 5 liters of blood per minute at rest, making 1,000 milliliters of oxygen available each minute. The importance of this oxygen reserve for physical activity and the body's ability to meet increased oxygen demands is emphasized.
Mindmap
Keywords
đĄCardiovascular System
đĄBlood Flow
đĄResistance
đĄVessel Radius
đĄPoiseuille's Law
đĄLocal Metabolic Conditions
đĄCapillary
đĄAutonomic Nervous System
đĄCardiac Output
đĄFrank-Starling Law of the Heart
đĄEjection Fraction
đĄArterial Venous Oxygen Difference (a-vO2 Difference)
Highlights
The video discusses the body's mechanism for blood distribution, focusing on blood flow, pressure differences, and resistance.
Resistance to blood flow is determined by blood viscosity, vessel length, and vessel radius, with P's law providing a precise relationship.
Vessel radius is the most crucial factor affecting resistance, with changes significantly impacting blood flow.
During exercise, the body rapidly adjusts blood flow to meet increased energy demands through local arterial dilation and neural signals.
Kidney function illustrates how the body adjusts regional blood flow, with a significant drop in blood supply during intense exercise.
Capillaries open more during exercise to increase muscle blood flow, improving gas and nutrient exchange.
Local vasodilation in skeletal and cardiac muscle is triggered by decreased tissue oxygen and other factors, reflecting higher metabolic needs.
The autonomic nervous system regulates blood vessel dilation and constriction, adjusting cardiovascular responses during activity.
Factors affecting venous return are crucial for balancing it with cardiac output, especially during upright physical activity.
Cardiac output is calculated by heart rate times stroke volume, with various methods developed for its assessment.
The Fick principle connects cardiac output to oxygen uptake and the arterial-venous oxygen difference.
The Frank-Starling law of the heart describes the increase in stroke volume in response to increased ventricular filling.
The ejection fraction is used to assess ventricular function and predict cardiovascular health outcomes.
Afterload influences stroke volume by requiring the ventricle to generate more pressure for aortic valve opening.
Blood flow to specific tissues varies according to metabolic demands, with the brain and heart requiring constant blood supply.
At rest, the distribution of cardiac output is highlighted, with the liver, kidneys, and muscles receiving the majority of the blood flow.
The body has a substantial oxygen reserve, even at rest, which serves as a reserve for sudden physical demands.
Transcripts
welcome to the next video in the series
comprising the anatomy and physiology
for the cardiovascular system we've just
discussed how the heart is controlled
now we will move to how the body
determines where the blood gets
distributed within the
body this video will provide you with
the information you require to be able
to address the following learning
objectives blood flow through a vessel
depends on pressure differences and
resistance resistance varies with the
vessel's length and diameter the longer
the vessel or the smaller the diameter
the greater the resistance the basic
relationship between flow pressure and
resistance is as follows flow equals
pressure divided by
resistance three factors determine
resistance to blood flow one blood
viscosity or how thick the blood is two
The Vessel length and three The Vessel
radius
P's law named after French physician
Jean Leonard Marie P describes this
relationship more
precisely it dictates that flow is equal
to the pressure gradient between two
points and the vessel radius to the
power of four all divided by The Vessel
length and the fluid
viscosity now since blood viscosity and
vessel length are relatively constant
vessel radius is the most crucial
factor harving a vessel's radius reduces
Flow by 16 times while doubling it
increases Flow by the same
factor this means even small changes in
vessel diameter can significantly impact
blood
flow when you exercise your body needs
to adjust blood flow rapidly to keep up
with increased energy demands nerves in
local metabolic conditions cause the
smooth muscle in in arterial walls to
change their diameter almost instantly
meanwhile neural signals make the veins
stiffer pushing blood from the
peripheral veins into the central
circulation during exercise more blood
flows to active muscles due to local
arterial dilation while other vessels
constract to reduce blood flow to less
critical
areas for example kidney function shows
how your body adjusts Regional blood
flow
at rest the kidneys get about a th000 Ms
of blood per minute which is about 20%
of the total cardiac output but during
intense exercise this drops to just 250
m per minute or just 1% of a 25 L
cardiac
output at rest only 1 in 30 to 40
capillaries and muscle tissue are open
during exercise more capillaries open
increasing muscle muscle blood flow
maintaining flow velocity with a small
increase in volume and improving gas and
nutrient exchange between blood and
muscle
fibers a decrease in tissue oxygen
triggers local vasodilation in sceletal
and cardiac muscle increased temperature
carbon dioxide acidic acidity sorry
adenosine nitric oxide and magnesium and
potassium ions also boost local blood
flow reflecting higher metabolism and
oxygen needs this local Vaso dilation is
the quickest way to increase oxygen
supply to
[Music]
tissues the autonomic nervous system
sympathetic and parasympathetic branches
centrally regulate blood vessel dilation
and
constriction for example sensy nerve
fibers and muscles respond to chemicals
released during activity sending signals
to the central nervous system to adjust
cardiovascular
responses simp athetic nerves end in the
muscular layers of small arteries
arterials and precapillary sphincter
releasing norepinephrine to constrict
blood vessels or acety choline to dilate
them continuous sympathetic nerve
activity maintains a state of Vaso
construction called vasom tone blood
vessel dilation occurs more from reduced
vasomotor tone than from increased
dilated fiber
activity sympathetic nerves also
stimulate the adrenal gland to release
epinephrine and a small amount of
norepinephrine these hormones mainly
cause constriction except in the heart
and sceletal muscle vessels however
their role in controlling blood flow
during exercise is minor compared to
local sympathetic neural
Drive factors affecting Venus return are
as important as those regulating
arterial blood flow muscle and breathing
actions along with visceral Vaso
constrict
help return blood to the right ventricle
balancing Venus return with cardiac
output during upright physical activity
gravity makes it harder for blood to
return from the extremity highlighting
the importance of Venus blood flow
regulation when we think about blood
flow within the cardiovascular system we
need to considered two important
components the amount ejected from the
heart per beat also known as the volume
and the total volume ejected per minute
which is our cardiac output let's start
by looking at the basic formula for
cardiac output which highlights that
cardiac output is related to heart rate
times the stroke volume this equation
highlights that the amount of blood the
heart pumps per minute depends on both
the rate of pumping I.E the heart rate
and the volume of blood ejected with HB
the stroke
volume there are a number of different
methods developed to assess cardiac
output many are quite invasive and few
are undertaken regularly outside of a
research or clinical
setting in 1870 German physiologist adol
Fick introduced a principle that
connects cardiac output to oxygen uptake
and the difference in oxygen content
between the arterial and Venus blood
while appearing quite simple and its
terms and measurements it is actually
quite complex to undertake
measuring oxygen consumption is
relatively easy and as your degree
progresses you'll undertake this
technique in second and third years
taking an arterial blood sample while
invasive is not actually that difficult
to do as accessing the radial artery is
quite easy but the most invasive
procedure is actually sampling the mixed
Venus blood now many of you might donate
blood regularly and think accessing a
vein is quite simple but to measure
mixed Venus blood need to access the
vein that collects all the Venus blood
from all over the body so this means
accessing the Venus system just before
it enters the right atrium which as you
can well imagine is not that easily
undertaken the thick equation helps us
understand the relationship between
cardiac output and the body's oxygen
needs let's consider an average sized
man his left ventricle pumps out his
entire 5 l blood volume every minute
this value although typical for many
individuals can vary significantly based
on one's cardiovascular
fitness for example a resting heart rate
of about 70 beats per minute sustains
the average adult's 5 L resting cardiac
output by substituting this heart rate
into our cardiac output equation we can
calculate the stroke
volume in this example 5,000 m of blood
divided by 70 beats gives a stroke
volume of approximately 71 m per
bead the phenomenon pictured here was
first described by Otto Frank and Ernest
Starling in the early 1900s and is known
as the Frank Starling law of the heart
it states that the heart stroke volume
increases in response to an increase in
the volume of blood filling the
heart the x-axis highlights how much
blood is contained within the ventricle
so moving to the right means more blood
in the
chamber the y- AIS is the resulting
stroke volume from that ventricle the
red line is the normal response with a
linear increase between the indolic
volume or the amount of blood in the
ventricle just before it contracts and
the resulting stroke volume this is when
the actin and mein cross bridges of the
cardiac muscle are at their most optimal
positioning pictured here
the length of the sarir is also
indicated on this figure and we can see
here that when the blood volume is low
there is too much
overlap a not efficient crossbridge
formation can occur then when the volume
of the blood within the chamber is too
high the cross Bridges become too
stretched and also cannot create
efficient crossbridge for
and stroke volume becomes less
optimal as reflected by the
decreasing
line during the cardiac cycle greater
ventricular filling occurs during Diest
through factors that increased Venus
return which is known as the preload or
a slowing of the heart rate an increase
in indolic volume stretches myocardial
fibers leading to a powerful ejection
stroke as the heart contracts
this expels both the normal stroke
volume and the additional blood that
filled the ventricles and is known as
the Frank Starling law clinicians use
the ejection fraction to assess
ventricular function and predict
cardiovascular health outcomes the
ejection fraction is the fraction of
blood pumped from the left ventricle
relative to its in enddiastolic
volume if the indolic volume is 110 Ms
and the stroke volume is 70 m mils the
ejection fraction is therefore
0.64 or
64% healthy individuals typically have
an ejection fraction between 50 and
70% and a lower ejection fraction often
indicates poor L left ventricular
function and a worse
prognosis okay now let's think of this
from a pressure within the ventricle and
the volume of the blood in that
ventricle if we focus on how much blood
is filling The ventricle we have two
important time points on the
x-axis the N systolic volume or
ESV and the N diastolic volume or edv
between these two time points is when
the heart is
filling and we know that this is when
our mitro valve
opens represented here by the blue dot
allowing blood
to flow from the Atria Into The
ventricle and when that mitro Veil
closes is the black dot the ventricular
cardiac muscle has started Contracting
at this point and once again is
developing an increase in pressure as it
contracts decreasing the size of the
ventricle until finally the aortic valve
opens at the pink dot here and blood is
ejected out of the heart
so using the volume pressure curves we
can see that by increasing the preload
as we described before in the Frank
styling mechanism of increasing the
stretch of the cardiac muscle fibers we
can increase the stroke volume by
increasing the volume of blood within
the ventricle at the end of The Filling
phase known as the end diastolic volume
this is represented in the top panel by
this gold
star whereas we can also increase the
stroke volume by decreasing the amount
of blood left in The ventricle at the
end of the systolic phase also known as
the end systolic volume this occurs
through a more forceful contraction of
The ventricle and is represented by the
star on the bottom
panel if we consider the influence of
afterload which is developed by an
increase in pressure within the arteries
increasing total peripheral resistance
of the system this then requires that
the ventricle must generate more
pressure to enable the aoic valve to
open and is represented by Point D on
the figure in the bottom right hand
panel the end result of an increase in
afterload is that the stroke volume is
reduced for that beit of the heart as we
can see in this decreased volume between
the point D and point
F at rest about 40 to 50% of the total
indolic blood volume remains in the left
ventricle after syy amounting to 50 to
70 M of blood during physical activity
the catacol means epinephrine and
norepinephrine increase myocardial
stroke power and systolic emptying
reducing this residual blood volume and
enhancing systolic
ejection blood flow to specific tissue
varies according to their metabolic
demands at rest the distribution of a 5
l the cardiac output is highlighted
within the figure below more than 1/4 of
blood flows to the liver about 1/5
flowing to the kidneys and muscles with
the remainder being distributed to the
heart skin brain and other
tissues the mardum and brain cannot
compromise their blood supplies at rest
the mardum uses 75% of the oxygen in the
blood flowing through the coronary
circulation to me increased oxygen
demands during activity coronary blood
flow must increase similarly cerebral
blood flow can increase by up to 30%
during physical activity compared to
rest with extra blood lightly directed
to motor function
areas at sea level each 100 Ms of
arterial blood carries about 20 M of
oxygen equating to 200 m per liter of
blood both trained and untrained adults
circulate about 5 L of blood per minute
at rest making 1,000 Ms of oxygen
available each
minute however resting oxygen uptake is
only about 250 m per minute leaving 750
Ms of oxygen unused which serves as a
reserve for sudden physical
demands this oxygen Reserve is further
indicated when we look at the thick equ
again within this the difference in
oxygen between the arterial blood and
the mixed Venus blood is highlighted by
the arterial venus oxygen difference or
represented here is the avo2 difference
at rest this difference is quite small
at only 5 m of oxygen per 100 m of blood
meaning there is substantial Reserve
remaining in this case 15 Ms of oxygen
per 100 Ms of blood or approximately 75%
of the original
value hopefully this video has now
provided you with the information you
require to be able to address the
following learning objectives
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