Transcript Cardiovascular Physiology

Cardiac Muscle
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Found only in heart
Striated
Each cell usually has one nucleus
Has intercalated disks and gap junctions
Autorhythmic cells
Action potentials of longer duration and longer
refractory period
Ca2+ regulates contraction
Cardiac Muscle
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Elongated, branching cells containing 1-2 centrally located nuclei
Contains actin and myosin myofilaments
Intercalated disks: Specialized cell-cell contacts
Desmosomes hold cells together and gap junctions allow action potentials
Electrically, cardiac muscle behaves as single unit
Cardiac myocyte action potential:
Refractory Period
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Absolute: Cardiac muscle cell completely
insensitive to further stimulation
Relative: Cell exhibits reduced sensitivity to
additional stimulation
Long refractory period prevents tetanic
contractions
AP-contraction relationship:
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AP in skeletal muscle is very
short-lived
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AP is basically over before an
increase in muscle tension can
be measured.
AP in cardiac muscle is very
long-lived
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AP has an extra component,
which extends the duration.
The contraction is almost over
before the action potential has
finished.
Functions of the Heart
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Generating blood pressure
Routing blood
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Ensuring one-way blood flow
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Heart separates pulmonary and systemic
circulations
Heart valves ensure one-way flow
Regulating blood supply
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Changes in contraction rate and force match
blood delivery to changing metabolic needs
Orientation of cardiac muscle fibres:
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Unlike skeletal muscles,
cardiac muscles have to
contract in more than
one direction.
Cardiac muscle cells are
striated, meaning they
will only contract along
their long axis.
In order to get
contraction in two axis,
the fibres wrap around.
Circulation circuits:
Heart Wall
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Three layers of tissue
Epicardium: This serous membrane of smooth
outer surface of heart
 Myocardium: Middle layer composed of cardiac
muscle cell and responsibility for heart
contracting
 Endocardium: Smooth inner surface of heart
chambers
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Valve function:
Coronary circulation:
Cardiac conducting system:
Pacemaker potential:
EKG:
Heart sounds:
Heart Sounds
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First heart sound or “lubb”
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Second heart sound or “dupp”
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Atrioventricular valves and surrounding fluid vibrations
as valves close at beginning of ventricular systole
Results from closure of aortic and pulmonary semilunar
valves at beginning of ventricular diastole, lasts longer
Third heart sound (occasional)
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Caused by turbulent blood flow into ventricles and
detected near end of first one-third of diastole
Cardiac Arrhythmias
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Tachycardia: Heart rate in excess of 100bpm
Bradycardia: Heart rate less than 60 bpm
Sinus arrhythmia: Heart rate varies 5% during
respiratory cycle and up to 30% during deep
respiration
Premature atrial contractions: Occasional
shortened intervals between one contraction
and succeeding, frequently occurs in healthy
people
Cardiac Cycle
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Heart is two pumps that work together, right
and left half
Repetitive contraction (systole) and relaxation
(diastole) of heart chambers
Blood moves through circulatory system
from areas of higher to lower pressure.
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Contraction of heart produces the pressure
Pressure relationships:
Mean Arterial Pressure (MAP)
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Average blood pressure in aorta
MAP=CO x PR
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CO is amount of blood pumped by heart per minute
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CO=SV x HR
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SV: Stroke volume of blood pumped during each heart beat
HR: Heart rate or number of times heart beats per minute
Cardiac reserve: Difference between CO at rest and
maximum CO
PR is total resistance against which blood must be
pumped
Factors Affecting MAP
Regulation of the Heart
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Intrinsic regulation: Results from normal functional
characteristics, not on neural or hormonal regulation
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Starling’s law of the heart
Extrinsic regulation: Involves neural and hormonal
control
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Parasympathetic stimulation
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Supplied by vagus nerve, decreases heart rate, acetylcholine
secreted
Sympathetic stimulation
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Supplied by cardiac nerves, increases heart rate and force of
contraction, epinephrine and norepinephrine released
Heart Homeostasis
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Effect of blood pressure
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Effect of pH, carbon dioxide, oxygen
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Chemoreceptors monitor
Effect of extracellular ion concentration
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Baroreceptors monitor blood pressure
Increase or decrease in extracellular K+ decreases heart
rate
Effect of body temperature
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Heart rate increases when body temperature increases,
heart rate decreases when body temperature decreases
Baroreceptor and Chemoreceptor
Reflexes
Cardian
innervation:
Pacemaker regulation:
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Once the pacemaker cells reach threshold, the
magnitude and duration of the AP is always the same.
In order to change the frequency, the time between APs
must vary.
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The interval can only be changed in two ways.
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The rate of depolarization can be changed
The amount of depolarization required to reach threshold can be
changed.
Vascular physiology:
Peripheral Circulatory System
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Systemic vessels
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Pulmonary vessels
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Transport blood through most all body parts
from left ventricle and back to right atrium
Transport blood from right ventricle through
lungs and back to left atrium
Blood vessels and heart regulated to ensure
blood pressure is high enough for blood flow
to meet metabolic needs of tissues
Blood Vessel Structure
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Arteries
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Elastic, muscular, arterioles
Capillaries
Blood flows from arterioles to capillaries
 Most of exchange between blood and interstitial
spaces occurs across the walls
 Blood flows from capillaries to venous system
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Veins
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Venules, small veins, medium or large veins
Structure of Arteries and Veins
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Three layers except for
capillaries and venules
Tunica intima (interna)
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Tunica media
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Endothelium
Vasoconstriction
Vasodilation
Tunica adventitia (externa)
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Merges with connective
tissue surrounding blood
vessels
Note mistake on figure
Structure of Arteries
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Elastic or conducting arteries
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Muscular or medium arteries
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Largest diameters, pressure high and fluctuates
Smooth muscle allows vessels to regulate blood
supply by constricting or dilating
Arterioles
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Transport blood from small arteries to capillaries
Structure of Veins
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Venules and small veins
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Medium and large veins
Valves
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Tubes of endothelium on delicate basement
membrane
Allow blood to flow toward heart but not in
opposite direction
Atriovenous anastomoses
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Allow blood to flow from arterioles to small
veins without passing through capillaries
Blood Vessel Comparison:
Capillaries:
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Capillary wall consists
mostly of endothelial
cells
Types classified by
diameter/permeability
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Continuous
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Fenestrated
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Do not have fenestrae
Have pores
Sinusoidal
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Large diameter with large
fenestrae
Capillary Network:
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Blood flows from
arterioles through
metarterioles, then
through capillary
network
Venules drain network
Smooth muscle in
arterioles, metarterioles,
precapillary sphincters
regulates blood flow
Muscular contractions aid venous return:
Pulmonary Circulation
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Moves blood to and from the lungs
Pulmonary trunk
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Pulmonary arteries
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Arises from right ventricle
Branches of pulmonary trunk which project to
lungs
Pulmonary veins
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Exit each lung and enter left atrium
Systemic Circulation: Arteries
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Aorta
From which all arteries are derived either directly or
indirectly
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Ascending, descending, thoracic, abdominal
Coronary arteries
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Supply the heart
Systemic Circulation: Veins
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Return blood from body to right atrium
Major veins
Coronary sinus (heart)
 Superior vena cava (head, neck, thorax, upper
limbs)
 Inferior vena cava (abdomen, pelvis, lower limbs)
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Types of veins
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Superficial, deep, sinuses
Dynamics of Blood Circulation
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Interrelationships between
Pressure
 Flow
 Resistance
 Control mechanisms that regulate blood pressure
 Blood flow through vessels
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Blood Pressure
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Measure of force exerted by blood against the
wall
Blood moves through vessels because of blood
pressure
Measured by listening for Korotkoff sounds
produced by turbulent flow in arteries as
pressure released from blood pressure cuff
Pressure and Resistance
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Blood pressure averages
100 mm Hg in aorta and
drops to 0 mm Hg in the
right atrium
Greatest drop in
pressure occurs in
arterioles which regulate
blood flow through
tissues
No large fluctuations in
capillaries and veins
Blood Pressure Measurement
Pulse Pressure
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Difference between
systolic and diastolic
pressures
Increases when stroke
volume increases or
vascular compliance
decreases
Pulse pressure can be
used to take a pulse to
determine heart rate
and rhythmicity
Blood Flow, Poiseuille’s Law
and Viscosity
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Blood flow
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Amount of blood moving
through a vessel in a given
time period
Directly proportional to
pressure differences,
inversely proportional to
resistance
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Poiseuille’s Law
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Flow decreases when
resistance increases
Flow resistance
decreases when vessel
diameter increases
Viscosity
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Measure of resistance
of liquid to flow
As viscosity increases,
pressure required to
flow increases
Critical Closing Pressure,
Laplace’s Law and Compliance
Critical closing pressure
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Pressure at which a blood
vessel collapses and blood
flow stops
Laplace’s Law
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Force acting on blood
vessel wall is proportional
to diameter of the vessel
times blood pressure
Vascular compliance
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Tendency for blood
vessel volume to
increase as blood
pressure increases
More easily the vessel
wall stretches, the
greater its compliance
Venous system has a
large compliance and
acts as a blood reservoir
Physiology of Systemic
Circulation
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Determined by
Anatomy of circulatory system
 Dynamics of blood flow
 Regulatory mechanisms that control heart and
blood vessels
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Blood volume
Most in the veins
 Smaller volumes in arteries and capillaries
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Laminar and Turbulent Flow
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Laminar flow
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Streamlined
Outermost layer
moving slowest and
center moving fastest
Turbulent flow
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Interrupted
Rate of flow exceeds
critical velocity
Fluid passes a
constriction, sharp turn,
rough surface
Aging of the Arteries
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Arteriosclerosis
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General term for
degeneration changes in
arteries making them
less elastic
Atherosclerosis
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Deposition of plaque
on walls
Capillary Exchange and
Interstitial Fluid Volume
Regulation
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Blood pressure, capillary permeability, and
osmosis affect movement of fluid from
capillaries
A net movement of fluid occurs from blood
into tissues. Fluid gained by tissues is removed
by lymphatic system.
Fluid Exchange Across
Capillary Walls
Vein Characteristics and
Effect of Gravity on Blood
Pressure
Vein Characteristics
 Venous return to heart
increases due to
increase in blood
volume, venous tone,
and arteriole dilation
Effect of Gravity
 In a standing position,
hydrostatic pressure
caused by gravity
increases blood
pressure below the
heart and decreases
pressure above the
heart
Control of Blood Flow by
Tissues
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Local control
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Nervous System
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In most tissues, blood flow is proportional to
metabolic needs of tissues
Responsible for routing blood flow and
maintaining blood pressure
Hormonal Control
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Sympathetic action potentials stimulate
epinephrine and norepinephrine
Local Control of Blood Flow
by Tissues
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Blood flow can increase 7-8 times as a result of vasodilation of
metarterioles and precapillary sphincters in response to increased
rate of metabolism
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Vasodilator substances produced as metabolism increases
Vasomotion is periodic contraction and relaxation of precapillary
sphincters
Nervous Regulation of
Blood Vessels
Short-Term Regulation of
Blood Pressure
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Baroreceptor reflexes
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Chemoreceptor reflexes
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Change peripheral resistance, heart rate, and stroke
volume in response to changes in blood pressure
Sensory receptors sensitive to oxygen, carbon dioxide,
and pH levels of blood
Central nervous system ischemic response
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Results from high carbon dioxide or low pH levels in
medulla and increases peripheral resistance
Baroreceptor Reflex Control
Local mechanisms affect MAP:
Effects of pH and Gases
Long-Term Regulation
of Blood Pressure
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Renin-angiotensin-aldosterone mechanism
Vasopressin (ADH) mechanism
Atrial natriuretic mechanism
Fluid shift mechanism
Stress-relaxation response
General control of MAP:
Renin-Angiotensin-Aldosterone
Mechanism
Vasopressin (ADH) Mechanism
Long Term Mechanisms
Which Lower Blood Volume
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Atrial natriuretic factor
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Hormone released from
cardiac muscle cells when
atrial blood pressure
increases, simulating an
increase in urinary
production, causing a
decrease in blood volume
and blood pressure
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Fluid shift
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Movement of fluid
from interstitial spaces
into capillaries in
response to decrease in
blood pressure to
maintain blood volume
Stress-relaxation
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Adjustment of blood
vessel smooth muscle to
respond to change in
blood volume
Chemoreceptor Reflex Control
Shock
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Inadequate blood flow throughout body
Three stages
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Compensated: Blood pressure decreases only a moderate
amount and mechanisms able to reestablish normal blood
pressure and flow
Progressive: Compensatory mechanisms inadequate and
positive feedback cycle develops; cycle proceeds to next stage
or medical treatment reestablishes adequate blood flow to
tissues
Irreversible: Leads to death, regardless of medical treatment
Fetal circulation: