chapter
5
The Cardiovascular
System and Its
Control
Major Cardiovascular Functions
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Delivery
Removal
Transport
Thermoregulation
Immune function
The Anatomy of the Human Heart
Myocardium—The Cardiac Muscle
• Thickness varies directly with stress placed on
chamber walls.
• Left ventricle is the most powerful of chambers and,
thus, the largest.
• With vigorous exercise, the size of the left ventricle
increases.
• Due to intercalated disks, impulses travel quickly in
cardiac muscle and allow it to act as one large muscle
fiber; all fibers contract together.
Coronary Circulation
Extrinsic Control of the Heart
• PNS acts through the vagus nerve to decrease heart rate
and force contraction.
• SNS is stimulated by stress to increase heart rate and
force of contraction.
• Epinephrine and norepinephrine—released due to
sympathetic stimulation—increase heart rate.
Did You Know . . . ?
Resting heart rates in adults tend to be between 60
and 85 beats per min. However, extended endurance
training can lower resting heart rate to 35 beats or
lower. This lower heart rate is thought to be due to
decreased intrinsic heart rate and increased
parasympathetic stimulation.
Intrinsic Conduction System of the
Heart
Cardiac Arrhythmias
Bradycardia is a resting heart rate below 60 bpm.
Tachycardia is a resting heart rate above 100 bpm.
Premature ventricular contractions (PVCs) feel like
skipped or extra beats.
Ventricular tachycardia involves three or more
consecutive PVCs that can lead to ventricular fibrillation
in which contraction of the ventricular tissue is
uncoordinated.
Did You Know . . . ?
The decrease in resting heart rate that occurs as an
adaptation to endurance training is different from
pathological bradycardia, an abnormal disturbance in
the resting heart rate.
Electrocardiogram
• Records the heart’s electrical activity and monitors
cardiac changes.
• The P wave represents atrial depolarization.
• The QRS complex represents ventricular depolarization
and atrial repolarization.
• The T wave represents ventricular repolarization.
Graphic Illustration of the Various Phases
of the Resting Electrocardiogram
Key Points
Structure and Function of the Cardiovascular System
• The two atria receive blood into the heart; the two
ventricles send blood from the heart to the rest of the
body.
• The left ventricle has a thicker myocardium due to
hypertrophy resulting from the force with which it must
contract.
• Cardiac tissue has its own conduction system through
which it initiates its own pulse without neural control.
(continued)
Key Points (continued)
Structure and Function of the Cardiovascular System
• The pacemaker of the heart is the SA node; it establishes
the pulse and coordinates conduction.
• The autonomic nervous system or the endocrine system
can alter heart rate and contraction strength.
• ECG records the heart’s electrical function and can be
used in diagnosing cardiac disorders.
Cardiac Cycle
• Defined as events that occur between two
consecutive heartbeats (systole to systole).
• Diastole is the relaxation phase during which the
chambers fill with blood (T waves to QRS).
• Systole is the contraction phase during which the
chambers expel blood (QRS to T wave).
Stroke Volume and Cardiac Output
Stroke Volume (SV)
• Volume of blood pumped per contraction
• End-diastolic volume (EDV)—volume of blood in
ventricle before contraction
• End-systolic volume (ESV)—volume of blood in
ventricle after contraction
• SV = EDV – ESV.
Cardiac Output (Q)
• Total volume of blood pumped by the ventricle per
minute
.
• Q = HR  SV
Ejection Fraction (EF)
• Proportion of blood pumped out of the left ventricle in
each beat
• EF = SV / EDV
• Averages 60% at rest
CALCULATIONS .
OF SV, EF, AND Q
The Vascular System
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Arteries
Arterioles
Capillaries
Venules
Veins
Did You Know . . . ?
Arteries always carry blood away from the heart; veins
always carry blood back to the heart with the help of
breathing, the muscle pump, and valves.
Blood Distribution Within the Vasculature
When the Body Is at Rest
The Muscle Pump
Blood Distribution
• Matched to overall metabolic demands
• Autoregulation—arterioles with organs or tissues dilate
or constrict
• Extrinsic neural control—sympathetic nerves within
walls of vessels are stimulated
• Determined by the balance between mean arterial
pressure and total peripheral resistance
.
RELATIVE DISTRIBUTION OF Q DURING
EXERCISE
.
ABSOLUTE DISTRIBUTION OF Q DURING
EXERCISE
Blood Pressure
• Mean arterial pressure (MAP) is the average pressure
exerted by the blood as it travels through arteries.
• MAP = DBP + [0.333  (SBP) – (DBP)]
• Blood vessel constriction increases blood pressure;
dilation reduces blood pressure.
Key Points
The Vascular System
• Blood returns to the heart with the help of
breathing, the muscle pump, and valves in the
veins.
• Blood is distributed throughout the body based on
the needs of tissues; the most active tissues
receive the most blood.
• Autoregulation controls blood flow by vasodilation
in response to local chemical changes in an area.
(continued)
Key Points (continued)
The Vascular System
• Extrinsic neural factors control blood flow primarily
by vasoconstriction.
• Systolic blood pressure (SBP) is the highest
pressure within the vascular system; diastolic
blood pressure (DBP) is the lowest.
• Mean arterial pressure (MAP) is the average
pressure on the arterial walls.
Functions of the Blood
• Transports gas, nutrients, and wastes
• Regulates temperature
• Buffers and balances acids and bases
Composition of Whole Blood
HEMOCONCENTRATION
Hematocrit
Ratio of formed elements to the total blood volume
• White blood cells protect body from disease
organisms.
• Blood platelets are cell fragments that help blood
coagulation.
• Red blood cells carry oxygen to tissues with the help
of hemoglobin.
Blood Viscosity
• Thickness of the blood
• The more viscous, the more resistant to flow
• Higher hematocrits result in higher blood viscosity
Key Points
Blood
• Blood and lymph transport materials to and from
body tissues.
• Blood is about 55% to 60% plasma and 40% to
45% formed elements (white and red blood cells
and blood platelets).
• Oxygen travels through the body by binding to
hemoglobin in red blood cells.
• An increase in blood viscosity results in resistance
to flow.