CVS 6 Blood Flow Regulation

Summary

This 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

• 🚀 The body regulates blood distribution based on pressure differences and resistance, with resistance varying by vessel length and diameter.
• 🔍 Flow, pressure, and resistance are interrelated, as described by the formula: Flow = Pressure / Resistance.
• 🌟 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.
• 🌱 Vessel radius is the most influential factor in blood flow, with small changes in diameter having significant effects on flow.
• 🏃‍♂️ During exercise, the body rapidly adjusts blood flow to meet increased energy demands, with local arterial dilation and neural signals affecting vein stiffness.
• 🍂 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.
• 🔄 Local vasodilation in skeletal and cardiac muscle is triggered by decreased tissue oxygen, increased temperature, and other metabolic byproducts.
• 🧠 The autonomic nervous system, including sympathetic and parasympathetic branches, centrally regulates blood vessel dilation and constriction.
• 💓 Cardiac output is calculated by multiplying heart rate by stroke volume, reflecting the heart's pumping efficiency.
• 📚 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.
• 💖 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

00:00

💓 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.

05:00

🏃‍♂️ 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.

10:01

🏥 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.

15:02

🌡️ 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.

Keywords

💡Cardiovascular System

The cardiovascular system is the body's network of organs that transport blood throughout the body, including the heart, blood vessels, and blood itself. It is central to the video's theme as it discusses how the heart and blood vessels function to distribute blood and oxygen to different parts of the body. The script mentions the control of the heart and the distribution of blood flow, highlighting the system's importance in maintaining life.

💡Blood Flow

Blood flow refers to the movement of blood through the circulatory system. It is a key concept in the video, which explains how blood flow is determined by pressure differences and resistance within the blood vessels. The script uses the term to describe the basic relationship between flow, pressure, and resistance, and how these factors are crucial for distributing blood to where it is needed in the body.

💡Resistance

Resistance in the context of the cardiovascular system is the opposition to blood flow through the blood vessels. The script explains that resistance varies with the vessel's length and diameter, and it is a critical factor in determining blood flow. It is used to illustrate how the body can regulate blood flow to different areas, such as during exercise when resistance in certain vessels changes to redirect blood flow.

💡Vessel Radius

Vessel radius is the distance from the center of a blood vessel to its wall. The script emphasizes that changes in vessel radius are the most significant factor affecting resistance and, consequently, blood flow. For example, the script states that halving a vessel's radius reduces flow by 16 times, while doubling it increases flow by the same factor, showing the impact of vessel radius on blood flow regulation.

💡Poiseuille's Law

Poiseuille's Law, named after French physician Jean Leonard Marie Poiseuille, is a principle that precisely describes the relationship between blood flow, pressure gradient, vessel radius, and fluid viscosity. The script uses this law to explain how blood flow is calculated and how vessel radius is a key determinant of flow, with a direct impact on the body's ability to regulate blood distribution.

💡Local Metabolic Conditions

Local metabolic conditions refer to the specific chemical and physical states within a particular area of the body that can influence blood flow. The script mentions that these conditions, such as changes in oxygen levels and the presence of certain chemicals, can cause the smooth muscle in arterial walls to change diameter, thus affecting blood flow to meet the area's metabolic needs.

💡Capillary

Capillaries are the smallest blood vessels in the body, connecting arterioles and venules, and facilitating the exchange of oxygen, nutrients, and waste products between the blood and tissues. The script explains that the number of open capillaries increases during exercise to improve blood flow and gas exchange with muscle fibers, demonstrating the body's adaptive response to increased metabolic demands.

💡Autonomic Nervous System

The autonomic nervous system is a part of the peripheral nervous system that controls involuntary bodily functions, including heart rate and blood vessel constriction or dilation. The script discusses how the sympathetic and parasympathetic branches of this system centrally regulate blood vessel responses, affecting blood flow and distribution throughout the body.

💡Cardiac Output

Cardiac output is the volume of blood pumped by the heart per minute, calculated as the product of heart rate and stroke volume. The script explains the formula for cardiac output and how it is related to the body's oxygen needs. It also discusses methods for assessing cardiac output, such as the Fick principle, which connects oxygen uptake and the difference in oxygen content between arterial and venous blood.

💡Frank-Starling Law of the Heart

The Frank-Starling law of the heart describes how the heart's stroke volume increases in response to an increase in the volume of blood filling the heart. The script uses this law to explain the heart's ability to adjust its output based on the preload, or the amount of blood in the ventricles just before contraction, which is a critical aspect of the heart's function in meeting the body's demands.

💡Ejection Fraction

Ejection fraction is a measure of the percentage of blood pumped out of the heart with each beat, relative to the volume of blood in the heart at the end of diastole. The script explains that a healthy ejection fraction is between 50 and 70%, and a lower fraction can indicate poor left ventricular function. This term is used to illustrate how clinicians assess the heart's ability to pump blood effectively.

💡Arterial Venous Oxygen Difference (a-vO2 Difference)

The arterial venous oxygen difference, or a-vO2 difference, is the difference in oxygen content between arterial blood and mixed venous blood. The script uses this concept to explain the body's oxygen reserve and how it can respond to sudden physical demands. It shows that even at rest, there is a significant amount of unused oxygen in the blood, which can be mobilized during activity.

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