Title: Chapter 19: Physiology of the Cardiovascular System
1Chapter 19 Physiology of the Cardiovascular
System
2 INTRODUCTION
- MAJOR FUNCTION OF THE CV SYSTEM DEPENDS ON
CONTINOUS AND CONTROLLED FLOW OF BLOOD THROUGH
CAPILLARIES - Major Function of the CV System Transportation
- Transportation depends on flow of blood through
capillaries - - Blood flow through capillaries must be
- Continuous ? To meet cells needs
- Controlled (changed) ? To meet the changing needs
of cells - How is this accomplished?
- Homoeostatic control mechanisms (hemodynamics)
- Hemodynamics collection of mechanisms that
influence the dynamic (active and changing)
circulation of blood
3Conduction System of the Heart
- Conduction system of the heart (Figure 19-2)
- System responsible for conducting nerve impulses
over the heart - The action potentials (impulses) of the heart
that trigger contractions must be coordinated
carefully. - Composed of four major structures (all modified
cardiac muscle) - Sinoatrial (SA) node
- Atrioventricular (AV) node
- AV bundle (bundle of His)
- Subendocardial branches (Purkinje fibers)
4Conduction System of the Heart (cont.)
- SINOATRIAL (SA) NODE
- Location in the right atrium near the opening of
the superior vena cava - Pacemaker of the Heart
- Nerve impulses start here
- Discharges a set of nerve impulses per minute
- ATRIOVENTRICULAR (AV) NODE
- Location in the right atrium along the
interatrial septum - ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS)
- Location originates in the AV node, spreads down
the interventricular septum in 2 branches - L R
- PURKINGE FIBERS
- Location extensions of the AV Bundle into the
walls of the ventricles
5Sequence of Cardiac Stimulation
- Specific sequence
- SA node discharges a nerve impulse ? travels to
LA and to AV node ? atria contract - Nerve impulse travels from AV node to AV bundle
(LR branches) to purkinge fibers ? ventricles
contract - Result 1 complete cardiac cycle (pumping cycle),
Assoc. with 1 heartbeat - Process repeats
- Interatrial bundle of conducting fibers
facilitates rapid conduction to left atrium - As signal enters AV node through internodal
bundles of conducting fibers, conduction slows,
permitting contraction of both atrial chambers
before impulse reaches the ventricles
6Electrocardiogram (ECG)
- Measures hearts electrical activity (graphic
record) - Provides a record of the electrical events that
precede the contractions of the heart - Electrodes of an electrocardiograph are attached
to the subject - Changes in voltage are recorded that represent
changes in the hearts electrical activity
(Figure 19-4) - EKG waves
- Normal waves
- P wave depolarization of the atria
- QRS complex depolarization of the ventricles,
repolarization of the atria - T wave repolarization of the ventricles
- Measurement of the intervals between P, QRS, and
T waves can provide information about the rate of
conduction of an action potential through the
heart - Clinical significance
- EKG can show problems related to the spread of
nerve impulses over the conduction system
7Cardiac Cycle
- Cardiac cycle a complete heartbeat consisting of
contraction (systole) and relaxation (diastole)
of both atria and both ventricles (5 steps) - The cycle is often divided into time intervals
- Step 1 Atrial systole
- Contraction of atria completes emptying of blood
out of the atria into the ventricles - AV valves are open semiluminar (SL) valves are
closed - Ventricles are relaxed and fill with blood
- This cycle begins with the P wave of the ECG
8Important Events of the Cardiac Cycle
- Step 2 Isovolumetric ventricular contraction
- Occurs between the start of ventricular systole
and the opening of the SL valves - Ventricular volume remains constant as the
pressure increases rapidly - Onset of ventricular systole coincides with the R
wave of the ECG and the appearance of the first
heart sound - Step 3 Ejection
- SL valves open and blood is ejected from the
heart when the pressure gradient in the
ventricles exceeds the pressure in the pulmonary
artery and aorta - Rapid ejection initial short phase characterized
by a marked increase in ventricular and aortic
pressure and in aortic blood flow - Reduced ejection characterized by a less-abrupt
decrease in ventricular volume coincides with
the T wave of the ECG
9Important Events of the Cardiac Cycle (cont.)
- Step 4 Isovolumetric ventricular relaxation
- Ventricular diastole begins with this phase
- Occurs between closure of the SL valves and
opening of the AV valves - A dramatic fall in intraventricular pressure but
no change in volume - The second heart sound is heard during this
period - Step 5 Passive ventricular filling
- Returning venous blood increases intra-atrial
pressure until the AV valves are forced open and
blood rushes into the relaxing ventricles - Influx lasts approximately 0.1 second and results
in a dramatic increase in ventricular volume - Diastasis later, longer period of slow
ventricular filling at the end of ventricular
diastole lasting approximately 0.2 second
characterized by a gradual increase in
ventricular pressure and volume
10Heart Sounds
- During each cardiac cycle the heart makes sounds.
- Systolic sound (contraction sound)
- First sound, believed to be caused primarily by
the contraction of the ventricles and vibrations
of the closing AV valves (step 2 of the cardiac
cycle) - Heart sound - lubb-dupp
- Diastolic sound (relaxation sound)
- short, sharp sound thought to be caused by
vibrations of the closing of SL valves - Step 4 of cardiac cycle
- Heart sound dupp
- Heart sounds have clinical significance because
they provide information about the functioning of
the valves of the heart - Heart murmur
- Abnormal heart sound - swishing
11PRIMARY PRINCIPLE OF CIRCULATION
- Blood flows because of a pressure gradient
- high pressure (aorta 100 mm Hg) ? low pressure
(venae cavae 0 mm Hg) - Pumping action causes fluctuation in aortic blood
pressure (systolic 120 mm Hg diastolic 80 mm Hg) - Blood circulates from the left ventricle to the
right atrium of the heart because of blood
pressure gradient - Measurement of blood flow is based on Newtons
first and second law of motion - P1-P2 is the symbol used to represent a pressure
gradient, with P1 representing the higher
pressure and P2 the lower pressure - Perfusion pressure pressure gradient needed to
maintain blood flow through a local tissue
12Arterial Blood Pressure
- High blood pressure must be maintained in the
arteries to keep blood flowing in the CV system - Primary determinant of arterial blood pressure is
the volume of blood in the arteries - A direct relation exists between arterial blood
volume and arterial pressure (Figure 19-10) - Cardiac output volume of blood pumped out of a
ventricle of the heart per unit of time (ml/min
or L/min) - General principles and definitions
- Cardiac output (CO) determined by stroke volume
and heart rate - Stroke volume (SV) volume pumped per heartbeat
- CO (volume/min) SV (volume/beat) ? HR
(beats/min) - In practice, CO is computed by Ficks formula
- Heart rate and SV determine CO, so anything that
changes either also tends to change CO, arterial
blood volume, and blood pressure in the same
direction
13Arterial Blood Pressure
- Relationship between arterial blood volume and
blood pressure.
14Factors That Affect Stroke Volume
- Starlings law of the heart (Frank-Starling
mechanism) - Mechanical factor that affects stroke volume
- The longer, or more stretched, the heart fibers
at the beginning of contraction, the stronger the
contraction (i.e. the more blood returned to the
heart, the stronger the contraction) - The amount of blood in the heart at the end of
diastole determines the amount of stretch placed
on the heart fibers - Exceptions Too much stretching of cardiac
muscle fibers has the opposite effect (i.e. makes
the contraction less strong) - The myocardium contracts with enough strength to
match its pumping load (within certain limits)
with each stroke, unlike mechanical pumps
15Factors that Affect Stroke Volume
- Contractility (strength of contraction) can also
be influenced by chemical factors (Figure 19-13) - Neural factors
- Norepinephrine
- Endocrine factors
- Epinephrine
- Mechanical factors
- Triggered by stress, exercise
16Factors that Affect Heart Rate
- SA node normally initiates each heartbeat BUT the
rate of the heartbeat can be altered - HOW?
- 1. Cardiac pressor reflexes (pressoreflexes)
- Receptors sensitive to changes in pressure
(baroreflexes) - Ex. aortic baroreceptors and carotid
baroreceptors - located in the aorta and carotid sinus
- Send afferent nerve fibers to cardiac control
centers in medulla oblongata - Work with integrators in the cardiac control
centers through negative feedback loop called
pressoreflexes or baroreflexes to oppose changes
in pressure by adjusting heart rate
17Factors that Affect Heart Rate (cont.)
- 2. Carotid sinus reflex (negative feedback loop)
- Sensory fibers from carotid sinus baroreceptors
run through the carotid sinus nerve and the
glossopharyngeal nerve to the cardiac control
center - Parasympathetic impulses leave the cardiac
control center, travel through the vagus nerve to
reach the SA node - Acetylcholine released from vagus fibers
decreases the rate of SA firing and heart rate - Vagal inhibition break of the heart
- Aortic reflex (negative feedback loop)
- Sensory fibers extend from baroreceptors located
in the wall of the arch of the aorta through the
aortic nerve and through the vagus nerve to
terminate in the cardiac control center - END RESULT Decreased heart rate
18Other Reflexes that Influence Heart Rate
? Heart Rate ? Heart Rate
Anxiety, fear, and anger Grief
Exercise Decreased blood temperature
Increased blood temperature Stimulation of skin cold receptors
Stimulation of skin heat receptors Norepinephrine (released from sympathetic response)
19Peripheral Resistance
- Helps determine aterial blood pressure
- Definition - resistance to blood flow imposed by
the force of friction between blood and the walls
of its vessels - Factors that influence peripheral resistance
- 1. Blood viscosity the thickness of blood as a
fluid - High plasma protein concentration can slightly
increase blood viscosity - High hematocrit can increase blood viscosity
- Anemia, hemorrhage, or other abnormal conditions
may also affect blood viscosity - Means blood meets friction as it flows
20Factors that Affect Peripheral Resistance
- 2. Diameter of arterioles (Figure 19-17)
- Vasomotor control mechanism muscles in walls of
arteriole may constrict (vasoconstriction) or
dilate (vasodilation), thus changing diameter of
arteriole - Controls amount of blood that runs from arteries
to arterioles - Small changes in blood vessel diameter cause
large changes in resistance - Means blood meets resistance in arteries as it
flows (ideal control system)
21Parts of the Vasomotor Control Mechanism
- Vasomotor center or vasoconstrictor center
area in the medulla - When stimulated initiates an impulse outflow by
sympathetic fibers that ends in the smooth
muscle surrounding resistant vessels, arterioles,
venules, and veins of the blood reserviors
causing their constriction - Vasomotor pressoreflexes
- Initiated by change in aterial blood pressure
- The change stimulates aortic and carotid
baroreceptors - Results in arterioles and venules of the blood
reservoirs dilating - Decrease in arterial blood pressure results in
stimulation of vasoconstrictor centers, causing
vascular smooth muscle to constrict
22Parts of the Vasomotor Control Mechanism (cont.)
- 3. Vasomotor chemoreflexes
- - chemoreceptors located in aortic and carotid
bodies are sensitive to hypercapnia, hypoxia, and
decreased arterial blood pH - 4. Medullary ischemic reflex
- - acts during emergency situation when blood
flow to the medulla is decreased causes marked
arteriole and venous constriction - 5. Higher brain centers
- - impulses from centers in cerebral cortex and
hypothalamus transmitted to vasomotor centers in
medulla to help control vasoconstriction and
dilation
23VENOUS RETURN TO THE HEART
- Venous return amount of blood returned to the
heart by the veins (venous blood deoxygenated
blood) - Affected by several factors
- Stress-relaxation effect occurs when a change in
blood pressure causes a change in vessel diameter
(because of elasticity) and thus adapts to the
new pressure to keep blood flowing (works only
within certain limits) - Gravity the pull of gravity on venous blood
- While sitting or standing tends to cause a
decrease in venous return (orthostatic effect) - Venous pumps help to overcome the influence of
gravity to maintain the pressure gradient of
blood - Pump unoxygenated blood back to the heart
- 2 kinds
- Respirations
- Skeletal muscle contractions
24Mechanisms of Venous Pumps
- Respirations Create pressure changes that act as
venous pumps - During inspiration pressure changes cause blood
to be pumped from abdominal vena cava to thoracic
vena cava - During expiration pressure changes cause blood
to be pumped into the atria - Skeletal muscle contractions promote venous
return by squeezing veins through a contracting
muscle and milking the blood toward the heart - Contraction squeezes veins within ? pumps blood
toward heart - One-way valves in veins prevent backflow
25Total Blood Volume
- Total blood volume changes in total blood volume
change the amount of blood returned to the heart - HOW?
- Capillary exchange governed by Starlings law of
the capillaries (Figure 19-26) - At arterial end of capillary, outward hydrostatic
pressure is strongest force moves fluid out of
plasma and into intracellular fluid - At venous end of capillary, inward osmotic
pressure is strongest force moves fluid into
plasma from intracellular fluid 90 of fluid
lost by plasma at arterial end is recovered - Lymphatic system recovers fluid not recovered by
capillary and returns it to the venous blood
before it is returned to the heart - Note If lymphatic system operates normally there
is no net loss of blood volume resulting from
capillary exchange
26Mechanisms that Change Total Blood Volume
- Mechanisms that change total blood volume most
quickly cause water to move into or out of the
plasma - Antidiuretic hormone mechanism
- Involves secretion/release of ADH (water
retention) - Increases TBV and venous return
- Renin- Angiotension Mechanism
- Involves secretion of aldosterone (sodium
retention followed by water retention) - Increases TBV and venous return
- Atrial natriuretic peptide mechanism
- Involves secretion of atrial natriuretic hormone
(sodium loss, followed by water loss) - Decreases TBV and venous return
27MEASURING BLOOD PRESSURE
- Arterial blood pressure
- Measured with a sphygmomanometer and stethoscope
listen for Korotkoff sounds as the pressure in
the cuff is gradually decreased (Figure 19-29) - Systolic blood pressure force of the blood
pushing against the artery walls while ventricles
are contracting - Diastolic blood pressure force of the blood
pushing against the artery walls when ventricles
are relaxed - Pulse pressure difference between systolic and
diastolic blood pressure
28MINUTE VOLUME OF BLOOD
- The volume of blood circulating through the body
per minute minute blood volume - Determined by magnitude of the blood pressure
gradient and peripheral resistance - Caculated based on mathematical equation
- (Poiseuilles Law) Minute volume Pressure
gradient (mean arterial BP - central venous BP) ?
Resistance - MV Minute Volume (volume of blood circulated
per minute) - BP Blood Pressure
- PR Peripheral Resistance
- PR Has 2 effects on circulation
- 1. PR can increase circ (increases artery blood
volume) - 2. PR can decrease circ (allows less blood to
flow) - Relation to arterial and venous bleeding
- Arterial bleeding blood escapes from artery in
spurts because of alternating increase and
decrease of arterial blood pressure - Venous bleeding blood flows slowly and steadily
because of low, nearly constant pressure
29FACTORS THAT INFLUENCE THE FLOW OF BLOOD
30VELOCITY OF BLOOD FLOW
- Velocity of blood is governed by the physical
principle that states when a liquid flows from an
area of one cross-sectional size to an area of
larger size, its velocity decreases in the area
with the larger cross section (Figure 19-31) - Blood flows fastest in arteries, slowest in
capillaries - Venule cross-sectional area is smaller than
capillary cross-sectional area, causing blood
velocity to increase in venules and veins
31PULSE
- Pulse alternate expansion and recoil of an
artery (Figure 19-32) - Causes LV contraction and relaxation
elasticity of artery walls - Clinical significance reveals important
information regarding the cardiovascular system,
blood vessels, and circulation - Physiological significance expansion stores
energy released during recoil, conserving energy
generated by the heart and maintaining relatively
constant blood flow (Figure 19-33) - Pulse wave
- Spread of pulse through arteries, each LV
contraction starts a new pulse wave that spreads
as a wave throughout arteries - Where is the pulse felt?
- Superficial arteries that lie over a firm surface
- Examples Radial artery, common carotid artery,
brachial artery - Venous pulse
- Detectable in large veins that lie near the heart
- Due to contraction/relaxation of the atria