Transcript ANPS 020 Black 01-29

Overview of the Cardiovascular System
Topics to be addressed:
Blood
Anatomy of Blood Vessels
Anatomy of the Heart
The Conduction System
The Cardiac Cycle
Cardiodynamics
Blood Flow and its Regulation
Adaptation and Disorders of the Cardiovascular System
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The Cardiovascular System:
Regulating Blood Flow
Organs must receive a steady
supply of oxygen and nutrients in
order to survive. Maintaining a
steady flow of blood to the organs is
the job of the cardiovascular
system.
Both the heart and the blood
vessels are capable of change in
order to adjust the flow of blood.
There are only 5 liters of blood in
the body, and it is constantly being
redistributed between different
organ systems
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Flow is a Function of
Pressure and Resistance
Blood Flow to tissues = Difference in blood pressure between heart and capillaries
Peripheral Resistance
Blood flows from a region of high pressure to one of lower
pressure; the greater the pressure difference driving the
movement, the greater the flow
The heart generates pressure to overcome resistance;
the greater the peripheral resistance, the lower the flow
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What produces the pressure in the
cardiovascular system?
Blood flows from
area of high
pressure to area of
low pressure
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What is meant by the term “Blood Pressure”
The pressure exerted by blood onto the vessel wall
Arterial Blood pressure (BP) : usually refers specifically to arterial pressure
Capillary hydrostatic pressure : Pressure within the capillary beds
Venous pressure : Pressure in the venous system
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Vessel pressure declines along the circuit
120 leaving left ventricle
<10 returning to right atrium
TERMS TO KNOW
Systolic Pressure : the peak arterial pressure during ventricular systole
Diastolic Pressure : the minimum arterial pressure during diastole
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Systolic and Diastolic Pressure in Elastic Arteries
During systole, the heart forces blood into the vessels and exerts great pressure on
the vessel walls.
During diastole, the heart is not pushing blood, but the recoil of the walls of the
elastic arteries continues to push blood and exert pressure.
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Elastic Arteries Have Different Pressures at
Systole and Diastole
TERMS TO KNOW
Pulse pressure : the difference between systolic pressure and diastolic pressure
Blood Pressure is Recorded in two ways:
1. Systolic/Diastolic Pressure
Typically 120/80
Hypertension : Abnormally high blood pressure (greater than 140/90)
Hypotension : Abnormally low blood pressure (less than 90/60)
2. Mean arterial pressure (MAP)= diastolic pressure + 1/3 pulse pressure; Typically 93
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Pulse Pressure Creates a Throbbing Sensation in the Artery
Pulse Points
Arteries large enough to
have pulse pressure
Arteries close enough to
skin surface to palpate
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Flow is a Function of
Pressure and Resistance
Where does RESISTANCE come from?
3 Sources :
1.
Vascular Resistance
• Due to friction between blood and the vessel wall
• Dependent on vessel length (constant) and diameter
(adjustable)
2.
Viscosity
• Resistance caused by molecules and suspended
materials in a liquid (cells, proteins, etc.) : blood is about 4
times more viscous than water
3.
Turbulence
• Swirling action within vessel that disturbs smooth flow
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Patterns of Blood Flow
Regulating Perfusion of
Tissues
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The main regulator of peripheral resistance is
vessel diameter
Arterioles, the smallest diameter
arteries, are the main site of regulation
of peripheral resistance
Changing vessel diameter on the
arterial side of the circuit changes
blood flow into organs
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Factors that affect pressure and resistance can
work locally (within a tissue) or systemically (in
blood, affecting all tissues)
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Summary : The two main forces at work in
regulation of blood flow
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Changing vessel diameter on the venous
side of the circuit influences preload
Recall that veins are the capacitance
vessels
There is more blood volume on the venous
side of circulation
Venous constriction redistributes blood flow
and enhances cardiac output
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Capillary Dynamics
Exchange of materials at capillaries is vital to homeostasis
Capillaries and their beds are OPTIMIZED for exchange
A continuous capillary,
the most common
capillary in the body, has
a wall one squamous
cell thick. Exchange
occurs across this wall.
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Capillary beds are optimized for exchange of materials :
the power in numbers
Although one capillary has the smallest diameter of any
vessel, there are so many of them that the TOTAL crosssectional area is higher at the capillary level than at any
other point of the circulation.
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Capillary beds are optimized for exchange of materials :
the power in numbers
The high cross-sectional area of the capillary circulation creates a drop in
pressure at that point of the circulation, and a decrease in flow velocity.
**These two features – low pressure and slow flow - optimize exchange in the
capillary beds.
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Capillary Dynamics
Exchange of materials at capillaries is vital to homeostasis
Once blood gets to the capillary, how does exchange of
materials with tissues occur?
3 forces at work moving materials across capillary walls:
• Diffusion
• Filtration
• Reabsorption
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Forces in Capillary Exchange : Diffusion
Diffusion: The movement of ions or molecules along a concentration gradient from
high concentration to low concentration
Diffusion Routes for important substances: Passive movement, so ongoing
Lipids and lipid-soluble materials such as O2 and CO2 diffuse through endothelial
plasma membranes
Some ions (Na+, K+, Ca2+, Cl-) diffuse through ion channels in plasma membranes
Water, ions, and small molecules such as glucose diffuse between adjacent
endothelial cells or through fenestrated capillaries
Large, water-soluble compounds like plasma proteins and blood cells are too big to
pass through continuous or fenestrated capillaries and can only get across the
big, leaky sinusoidal capillaries.
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Variable Forces in Capillary Exchange :
Filtration and Reabsorption
Filtration:
Water and small
solutes squeezed out
of the capillary into the
interstitial fluid
Reabsorption:
Driven by blood
pressure (capillary
hydrostatic pressure)
Pulled by osmotic
pressure exerted by
large plasma proteins
trapped in blood
Water drawn back into
the capillary from the
interstitial fluid
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Forces in Capillary Exchange
How does the Filtration Force change across a capillary bed?
Capillary Hydrostatic Pressure (CHP) at arterial end 35 mmHg
Capillary Hydrostatic Pressure at venous end is 21 mmHg
Filtration pressure declines as blood moves across capillary bed
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Forces in Capillary Exchange
How does the Reabsorptive Force change across a capillary bed?
Plasma proteins are trapped in blood, so exert a constant force along the bed
This force is called the colloid osmotic pressure (COP)
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Forces in Capillary Exchange
Net Filtration Pressure (NFP) is the difference between
net hydrostatic pressure and net osmotic pressure
(how much is pushed out minus how much is drawn back in)
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Forces in Capillary Exchange
Net Filtration Pressure changes along the length of the capillary
– At arterial end of capillary, fluid moves out of capillary, into interstitial fluid
– At venous end of capillary, fluid moves into capillary, out of interstitial fluid
– These movements are not equal
RESULT:
Normally capillaries filter more
than they reabsorb
up to 3 liters of fluid per day leave
the blood and collect in the tissues
without being reabsorbed; how is
this fluid recovered?
Picture from different textbook, so
different NFP numbers, but the pattern
is the same
Recovery of interstitial fluid
Lymphatic vessels return interstitial fluid to the bloodstream
– A separate set of vessels; do not carry blood
– One way drainage system, not a “lymphatic circuit”
Interstitial fluid collected into lymphatic vessels is called lymph
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Recovery of interstitial fluid
Lymphatic fluid is drained through a series
of lymphatic vessels and returned to
the blood stream close to the heart.
Lymph nodes
interspersed along the
lymphatic channels
serves as filters to
remove pathogens
before the lymph is
returned to the
bloodstream
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Failure of the lymphatic system to return interstitial
fluid results in edema
Elephantiasis is
caused by a parasitic
infection which invades
and blocks lymphatic
vessels
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Disorders Often Affect Capillary Dynamics
1. Hemorrhage
decrease in BP reduces CHP and NFP
net increase in reabsorption of interstitial fluid (recall of fluids)
2. Cardiac failure
Pitting edema
decrease in stroke volume backs blood up
into venous circulation, increasing CHP and
NFP, leading to edema
3. Dehydration
Increases blood osmotic pressure, decreasing NFP
Accelerates reabsorption
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Cardiovascular Regulation
Goal is to maintain Tissue Perfusion (Blood flow through the tissues)
Deliver O2 and nutrients to tissues and organs
Remove CO2 and wastes from tissues
Flow is affected by
• Cardiac output
• Peripheral resistance
• Blood pressure
Cardiovascular regulation changes blood flow to a specific area
Different organs have different metabolic needs at different times
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Cardiovascular Regulation
3 Factors Influence Cardiac Output and Blood Pressure
– Autoregulation
• Causes immediate, localized homeostatic adjustments
– Neural mechanisms
• Respond quickly to changes at specific sites
– Endocrine mechanisms
• Slowest, direct long-term changes
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Cardiovascular Regulation : Autoregulation
Local Regulation of Blood Flow within Tissues
: Adjusted by changing peripheral resistance while
cardiac output stays the same; the main effect is to
change the diameter of the blood vessel wall
Local vasodilators increase local blood flow
some are local chemical changes in busy tissues
some are chemicals released by inflammation
(histamine)
elevated local temperature is an additional factor
Local vasoconstrictors decrease local blood
flow
some are local chemical changes in quiet tissues
some are chemicals released by damaged tissues
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Cardiovascular Regulation : Fast Alterations
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Cardiovascular Regulation :
Neural Reflexes respond to changes in flow and
the chemicals in the blood
The Cardiovascular Center in the brainstem monitors the state of the bloodstream
(sensory input) and adjusts the performance of organs (motor).
Baroreceptor reflexes respond
to changes in blood pressure
Chemoreceptor reflexes
respond to changes in chemical
composition, particularly pH
and dissolved gases
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Cardiovascular Regulation :
The Baroreceptor Reflex is a Neural Mechanism
Input:
sensory feedback from
aortic arch and carotid
body
Integration:
cardiovascular center of
medulla decides what
adjustments need to be
made
Output:
1. alterations in balance
of sympathetic and
parasympathetic output
to heart to adjust
cardiac output
2. Alteration in
sympathetic output to
blood vessels
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Cardiovascular Regulation : Baroreceptor Reflex
Cardiovascular center
Cardiovascular center
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Longer Term Cardiovascular Regulation : Hormones
affecting kidney have profound effects on cardiovascular
function
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