The Cardiovascular System
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Anatomy of the Heart
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Heart functions:
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Keeps O2-poor blood separate from
O2-rich blood
Keeps the blood flowing in one
direction
Creates blood pressure
Regulates the blood supply
Anatomy of the Heart
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The Wall and Coverings of the Heart
Pericardium
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Two-layered serous membrane that encloses the heart
Myocardium
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Thickest part of heart wall
Made of cardiac muscle
Endocardium
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Inner layer of heart
Pericardial fluid
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Reduces friction as the heart beats
The coverings of the heart:
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Protect the heart
Confine it to its location
Prevent it from overfilling
Fig 12.2
Anatomy of the Heart
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Chambers of the Heart
Right atrium
Receives O2-poor blood
Vessels that empty into right atrium:
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Superior vena cava
Inferior vena cava
Coronary sinus
Venous blood leaves right atrium through the an
atrioventricular (AV) valve (tricuspid)
Directs the flow of blood
Prevents backflow
Has three cusps
Right ventricle
Chordae tendineae
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Fibrous cords connected to the tricuspid valve
Blood passes through the pulmonary semilunar
valve into the pulmonary trunk
Anatomy of the Heart
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Left atrium
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Receives O2-rich blood
Blood enters atrium through 4 pulmonary
veins
Blood leaves left atrium through an AV
valve (bicuspid or mitral)
Left ventricle
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Forms the apex of the heart
Blood leaves the left ventricle through the
aortic semilunar valve and enters the
aorta
Fig 12.3
Anatomy of the Heart
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Operation of the Heart Valves
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AV valves
Normally open
When ventricle contracts
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AV valves shut
Semilunar valves
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Normally closed
Contraction of ventricles forces valves
open
Anatomy of the Heart
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Heart Sounds
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First sound, “lub”
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Heard when ventricles begin to contract
AV valves close
Lasts longer and has a lower pitch
Second sound, “dup”
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When ventricles relax
Semilunar valves close
Heart murmurs
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Due to ineffective, leaky valves
Valves do not close properly
Allows blood to backflow into atria or
ventricles after valves have closed
Anatomy of the Heart
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Coronary Circulation
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Heart cells are not nourished by the blood in
the chambers
The left and right coronary arteries branch
from the aorta
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Coronary arteries branch numerous times
Heart is encircled by small blood vessels
After blood passes through cardiac
capillaries it enters the cardiac veins
Cardiac veins enter the coronary sinus
Coronary sinus enters the right atrium
Fig 12.4
Physiology of the Heart
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Conduction System of the Heart
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Initiates and stimulates contraction of
the atria and ventricles
Is intrinsic – does not require nervous
stimulation
Coordinates contraction of atria and
ventricles
Physiology of the Heart
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Nodal Tissue
Has muscular and nervous characteristics
SA (sinoatrial) node – upper posterior
wall of the right atrium
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AV (atrioventricular) node – base of the
right atrium
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Initiates the heartbeat
Sends out an excitation impulse every 0.85
seconds
Pacemaker of the heart
Signals the ventricles to contract
Atrioventricular bundle (AV bundle)
Purkinje fibers
Fig 12.5
Physiology of the Heart
Artificial pacemaker may be implanted if
the SA node fails to work properly
Heart block – slow beating of the heart
due to a damaged AV node
Ectopic pacemaker
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An area other than the SA node that can
become the pacemaker
May cause an extra beat
Caffeine and nicotine can stimulate an ectopic
pacemaker
Electrocardiogram
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Electrolyte changes within the myocardium can
be detected by electrical recording devices
Helps a physician detect and diagnose the
cause of an irregular heartbeat (arrhythmias)
Physiology of the Heart
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Cardiac Cycle
All events that occur during one heartbeat
Systole – contraction of heart muscle
Diastole – relaxation of heart muscle
Three phases of the cardiac cycle:
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Phase 1: Atrial Systole
Both atria are in systole
Ventricles are in diastole
Both AV valves are open
The semilunar valves are closed
Phase 2: Ventricular Systole
Both ventricles are in systole
The atria are in diastole
Semilunar valves are forced open
Both AV valves are closed
Phase 3: Atrial and Ventricular Diastole
Both atria and both ventricles are in diastole
Both AV valves are open
The semilunar valves are closed
Fig 12.6
Physiology of the Heart
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Cardiac Output (CO)
Volume of blood pumped out of a ventricle in one
minute
Average CO is 5,250 ml/minute
Dependent on two factors:
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Heart rate
Beats per minute
Can be altered by the autonomic nervous system
Temperature affects the heart rate
Proper electrolytes are needed to keep the heart
rate regular
Stroke volume
Amount of blood pumped by a ventricle each
time it contracts
Depends on the strength of contraction
Influenced by blood electrolyte concentration
and the activity of the autonomic nervous
system
Venous return and difference in blood pressure
also affect the strength of contraction
Fig 12.7
Anatomy of Blood Vessels
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Vessels function to:
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Transport blood and its contents
Carry out gas exchange
Regulate blood pressure
Direct blood flow
Arteries and Arterioles
Anatomy of Blood Vessels
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Arteries and Arterioles
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Transport blood away from the heart
Thick, strong walls composed of:
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Tunica interna - endothelium
Tunica media – smooth muscle and elastic fibers
Tunica externa – outer connective tissue layer
Elasticity allows an artery to expand and
recoil
Arterioles are small arteries
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Constriction and dilation affect blood distribution
and blood pressure
Autonomic nervous system regulates the number
of arterioles that are contracted
Anatomy of Blood Vessels
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Capillaries
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Microscopic blood vessels
One layer of endothelial cells
Site of nutrient and gas exchange
Not all capillary beds are in use at the
same time
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Most have a shunt
Precapillary sphincters control the
entrance of blood into capillaries
Fig 12.9
Anatomy of Blood Vessels
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Veins and Venules
Return blood to the heart
Venules
Drain blood from the capillaries
Join together to form veins
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Vein walls are thinner than arterial walls
Valves in veins prevent backward flow of
blood
Varicose veins and phlebitis
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Varicose veins
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Abnormal and irregular dilations in superficial veins
Hemorrhoids are varicose veins in the rectum
Develop when the valves of the veins become weak
Phlebitis
Inflammation of a vein
Thromboembolism can occur
Fig 12.8
Physiology of Circulation
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Velocity of Blood Flow
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Slowest in capillaries
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Cross-sectional area is at its maximum
Allows time for gas and nutrient exchange
Blood flow increases as venules
combine to form veins
Velocity of blood returning to the
heart is low compared to that of blood
leaving the heart
Fig 12.10
Physiology of Circulation
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Blood Pressure
The force of blood against blood vessel walls
Highest in the aorta
Decreases with distance from left ventricle
and is lowest in the venae cavae
Fluctuates between systolic blood pressure
and diastolic blood pressure
Mean arterial blood pressure
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Pressure in the arterial system averaged over time
Equals cardiac output x peripheral resistance
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Increasing CO increases MABP
Peripheral resistance is the resistance to flow
between blood and the walls of a blood vessel
The smaller the blood vessel or the longer the
blood vessel the greater the resistance
The greater the resistance the higher the blood
pressure
Fig 12.11
Physiology of Circulation
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Blood pressure and cardiac output
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The faster the heart rate the greater the
cardiac output
As cardiac output increases, blood
pressure increases
The larger the stroke volume, the greater
the blood pressure
Stroke volume and heart rate increase
blood pressure only if the venous return
is adequate
Physiology of Circulation
Venous return depends on:
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A blood pressure difference
The skeletal muscle pump and the respiratory
pump
Contraction of skeletal muscles compress
the walls of veins causing blood to move
past a valve
During inhalation, thoracic pressure falls
and abdominal pressure rises and blood will
flow from an area of higher pressure to an
area of lower pressure
Total blood volume
If blood volume decreases, blood pressure
falls
If blood volume increases, blood pressure
rises
Fig 12.12
Physiology of Circulation
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Blood pressure and peripheral resistance
Neural regulation of peripheral resistance
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Vasomotor center regulates vasoconstriction
Also causes blood to be shunted from one area of
the body to another
Hormonal regulation of peripheral resistance
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Epinephrine and norepinephrine increase heart rate
and constrict arterioles
Renin-angiotensin-aldosterone system
Angiotensin II constricts the arterioles
Aldosterone causes the reabsorption of sodium
and water in the kidneys
Antidiuretic hormone causes the reabsorption of
water and vasoconstriction
Atrial natriuretic hormone inhibits renin and
aldosterone secretion
Fig 12.13
Physiology of Circulation
• Evaluating circulation
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Pulse
 Alternating
expansion and recoil
of arterial walls
 Can be felt in
superficial arteries
(pulse points)
- Radial artery
- Common carotid
 Pulse rate normally
indicates the rate of
the heartbeat
Fig 12.14
Physiology of Circulation
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Blood pressure
 Usually measured in
brachial artery
 Sphygmomanometer is an
instrument that records
pressure changes
 The blood pressure cuff is
inflated until no blood flows
through the artery
 Korotkoff sounds
- produced when the
pressure in the cuff is
released and blood
begins to hit the arterial
walls
- Systolic pressure
- When sounds end
diastolic pressure is
recorded
Fig 12.15
Physiology of Circulation
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Normal blood pressure is 120/80
Higher number is systolic pressure –
pressure recorded when the left ventricle
contracts
Lower number is diastolic pressure –
pressure recorded when the left ventricle
relaxes
Hypertension is high blood pressure
When the systolic pressure is 140 or greater
When the diastolic pressure is 90 or greater
Circulatory Routes
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Pulmonary circuit
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Blood from the body collects in the
right atrium
Blood moves into the right ventricle
Right ventricle pumps blood into the
pulmonary trunk
Blood flows into the pulmonary
capillaries in the lungs
Blood flows from the lungs through
the pulmonary veins and into the left
atrium
Circulatory Routes
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Congestive Heart Failure
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Damaged left side of the heart fails to pump
adequate blood
Blood backs up in the pulmonary circuit
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Pulmonary blood vessels have become congested
Causes pulmonary edema
Indicated by shortness of breath, fatigue,
and a constant cough
Treatment
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Diuretics – increase urinary output
Digoxin – increases the heart’s contractile force
Dilators – relax blood vessels
Circulatory Routes
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Systemic circuit
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Includes all other arteries and veins of the
body
Aorta and venae cavae are the major
pathways for blood in the systemic circuit
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Aorta is the largest artery
Superior and inferior venae cavae are the largest
veins
Begins in the left ventricle
The left ventricle pumps blood into the aorta
Branches from the aorta go to the major
body regions and organs
Circulatory Routes
Table 12.1
Fig 12.16
Circulatory Routes
Table 12.2
Fig 12.17
Circulatory Routes
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Special Systemic Circulations
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Hepatic Portal System
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Carries venous blood from the stomach,
intestines, and other organs to the liver
Capillaries of the digestive tract empty into the
superior mesenteric and the splenic veins
Superior mesenteric and splenic vein join to form
the hepatic portal vein
Gastric veins empty into the hepatic portal vein
Nutrients and wastes diffuse into liver cells
The hepatic veins drain the liver and enter the
inferior vena cava
Fig 12.18
Circulatory Routes
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Hypothalamus-Hypophyseal Portal
System
Blood Supply to the Brain
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Anterior and posterior cerebral arteries
and the carotid arteries supply the brain
with arterial blood
Cerebral arterial circle (circle of Willis)
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The blood vessels form a circle
Provides alternate routes for supplying arterial
blood to the brain
Equalizes blood pressure in the brain’s blood
supply
Fig 12.19
Circulatory Routes
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Fetal Circulation
Four circulatory features not present in adult circulation
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Foramen ovale
Ductus arteriosus
Umbilical arteries
Ductus venosus
Related to the fact that the fetus does not use its lungs
Path of blood in the fetus
From the right atrium
Most blood enters the left atrium via the foramen ovale
Blood that has entered the right ventricle and then the
pulmonary trunk is shunted to the aorta through the
ductus arteriosus
Exchange between maternal and fetal blood occurs at the
placenta
Blood in the umbilical arteries is oxygen poor
Blood in the umbilical veins is oxygen rich
Enters the ductus venosus
The ductus venosus then joins with the inferior vena
cava
Fig 12.20
Effects of Aging
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Heart
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Grows larger with age
In many middle-aged people, heart is
covered by a layer of fat
Number of collagenous fibers in the
endocardium increases
Valves become thicker and more rigid
The myocardium loses contractile
power and ability to relax
Resting heart rate decrease
Effects of Aging
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Arteries
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Atherosclerosis and arteriosclerosis
are common
Chances of coronary thrombosis and
heart attack increase
Occurrence of varicose veins
increases
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Thromboembolism
Pulmonary embolism
Homeostasis
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Maintaining blood composition, pH, and
temperature
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Growth factors regulate the manufacture of
formed elements in the red bone marrow
The digestive system absorbs nutrients into
the blood
The lungs and kidneys remove metabolic
wastes from the blood
The kidneys help maintain the pH of blood
The blood distributes heat
Blood vessels in the skin dilate or constrict
in response to changing temperatures
Homeostasis
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Maintaining blood pressure
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Sensory receptors within the aortic
arch detect a decrease in blood
pressure
The lymphatic system collects excess
tissue fluid, which helps regulate
blood volume and pressure
The endocrine and nervous systems
work together to regulate blood
pressure
Venous return is aided by the
muscular and respiratory systems