Chapter 18

Cardiovascular System
Anatomy and Physiology
Two children were sitting outside a clinic. One of
them was crying very loudly.
2nd Child: Why are you crying?
1st Child: I came here for a blood test.
2nd Child: So? Are you afraid?
1st Child: No. For the blood test, they cut my
At this, the second one started crying
The first one was astonished.
1st Child: Why are you crying now?
2nd Child: I came for a urine test!
Overview of Blood Circulation
Blood leaves the heart via arteries that branch
repeatedly until they become capillaries
Oxygen (O2) and nutrients diffuse across capillary
walls and enter tissues
Carbon dioxide (CO2) and wastes move from tissues
into the blood
Oxygen-deficient blood leaves the capillaries and
flows in veins to the heart
This blood flows to the lungs where it releases CO2
and picks up O2
The oxygen-rich blood returns to the heart
Composition of Blood
Blood is the body’s only fluid tissue
 It is composed of liquid plasma and formed elements
 Formed elements include:
– Erythrocytes, or red blood cells (RBCs)
– Leukocytes, or white blood cells (WBCs)
– Platelets (Thrombocytes)
Hematocrit – the percentage of RBCs out of the total
blood volume
Composition of Blood
Figure 18.1
Physical Characteristics and
Blood is a sticky, opaque fluid with a metallic taste
Color varies from scarlet (oxygen-rich) to dark red
The pH of blood is 7.35–7.45
Temperature is 38C, slightly higher than “normal”
body temperature
Blood accounts for approximately 8% of body weight
Average volume of blood is 5–6 L for males, and 4–5
L for females
Functions of Blood
Blood performs a number of functions
dealing with:
– Substance distribution
– Regulation of blood levels of particular
– Body protection
Blood Plasma
Blood plasma contains over 100 solutes, including:
– Proteins – albumin, globulins, clotting proteins, and others
– Nonprotein nitrogenous substances – lactic acid, urea,
– Organic nutrients – glucose, carbohydrates, amino acids
– Electrolytes – sodium, potassium, calcium, chloride,
– Respiratory gases – oxygen and carbon dioxide
Erythrocytes (RBCs)
Biconcave discs, anucleate,
essentially no organelles
 Filled with hemoglobin (Hb), a
protein that functions in gas
 Contain the plasma membrane
protein spectrin that:
– Gives erythrocytes their flexibility
– Allows them to change shape as
Figure 18.3
Erythrocyte Function
Erythrocytes are dedicated to respiratory gas transport
 Hemoglobin reversibly binds with oxygen and most
oxygen in the blood is bound to hemoglobin
 Hemoglobin is composed of:
– The protein globin, made up of two alpha and two beta
chains, each bound to a heme group
– Each heme group bears an atom of iron, which can bind one
to oxygen molecule
Each hemoglobin molecule can transport four
molecules of oxygen
Erythrocyte Function
Figure 18.4a, b
Hormonal Control of
Erythropoietin (EPO) release by the kidneys is
triggered by:
– Hypoxia due to decreased RBCs
– Decreased oxygen availability
– Increased tissue demand for oxygen
Enhanced erythropoiesis increases the:
– RBC count in circulating blood
– Oxygen carrying ability of the blood increases
Hormonal Control of
Figure 18.6
Life Cycle of Red Blood Cells
Figure 18.7
Leukocytes (WBCs)
Leukocytes, the only blood components that are
complete cells:
Are less numerous than RBCs
Make up 1% of the total blood volume
Can leave capillaries via diapedesis
Move through tissue spaces
Leukocytosis – WBC count over 11,000 per
cubic millimeter
– Normal response to bacterial or viral invasion
Platelets are fragments of megakaryocytes with a bluestaining outer region and a purple granular center
 The granules contain serotonin, Ca2+, enzymes, ADP,
and platelet-derived growth factor (PDGF)
 Platelets function in the clotting mechanism by forming
a temporary plug that helps seal breaks in blood vessels
White blood cells
Red blood cells
Sickle cell anemia
A series of reactions designed for stoppage of
 During hemostasis, three phases occur in rapid
– Vascular spasms – immediate vasoconstriction in
response to injury
– Platelet plug formation
– Coagulation (blood clotting)
Blood Typing
When serum containing anti-A or anti-B agglutinins is
added to blood, agglutination will occur between the
agglutinin and the corresponding agglutinogens
 Positive reactions indicate agglutination
Heart Anatomy
Approximately the size of your fist
 Location
– Superior surface of diaphragm
– Left of the midline
– Anterior to the vertebral column, posterior to the
Heart Anatomy
Figure 19.1
Heart Covering
Pericardial physiology
– Protects and anchors heart
– Prevents overfilling
Figure 19.2
Heart Covering
Pericardial anatomy
– Fibrous pericardium
– Serous pericardium (separated by pericardial cavity)
– Epicardium (visceral layer)
Figure 19.2
Heart Wall
Epicardium – visceral layer of the serous pericardium
 Myocardium – cardiac muscle layer forming the bulk of
the heart
 Fibrous skeleton of the heart – crisscrossing, interlacing
layer of connective tissue
 Endocardium – endothelial layer of the inner
myocardial surface
External Heart: Anterior View
Figure 19.4b
Atria of the Heart
Atria are the receiving chambers of the heart
 Each atrium has a protruding auricle
 Pectinate muscles mark atrial walls
 Blood enters right atria from superior and
inferior venae cavae and coronary sinus
 Blood enters left atria from pulmonary veins
Ventricles of the Heart
Ventricles are the discharging chambers of
the heart
 Papillary muscles and trabeculae carneae
muscles mark ventricular walls
 Right ventricle pumps blood into the
pulmonary trunk
 Left ventricle pumps blood into the aorta
Gross Anatomy of Heart: Frontal
Figure 19.4e
Pathway of Blood through the
Heart and Lungs
Right atrium  tricuspid valve  right ventricle
 Right ventricle  pulmonary semilunar valve 
pulmonary arteries  lungs
 Lungs  pulmonary veins  left atrium
 Left atrium  bicuspid valve  left ventricle
 Left ventricle  aortic semilunar valve  aorta
 Aorta  systemic circulation
Pathway of Blood through the
Heart and Lungs
Figure 19.5
Heart Valves
Heart valves insure unidirectional blood flow through
the heart
 Atrioventricular (AV) valves lie between the atria and
the ventricles
 AV valves prevent backflow into the atria when
ventricles contract
 Chordae tendineae anchor AV valves to papillary
Heart Valves
Figure 19.9
Heart Valves
Aortic semilunar valve lies between the left ventricle
and the aorta
 Pulmonary semilunar valve lies between the right
ventricle and pulmonary trunk
 Semilunar valves prevent backflow of blood into the
Heart Valves
Figure 19.10
Heart Physiology: Sequence
of Excitation
Sinoatrial (SA) node generates impulses about 75
 Atrioventricular (AV) node delays the impulse
approximately 0.1 second
 Impulse passes from atria to ventricles via the
atrioventricular bundle (bundle of His)
Heart Physiology: Sequence
of Excitation
AV bundle splits into two pathways in the
interventricular septum (bundle branches)
– Bundle branches carry the impulse toward the apex
of the heart
– Purkinje fibers carry the impulse to the heart apex
and ventricular walls
Heart Physiology: Sequence
of Excitation
Figure 19.14a
Electrical activity is recorded by electrocardiogram
P wave corresponds to depolarization of atria
QRS complex corresponds to ventricular depolarization
T wave corresponds to ventricular repolarization
Atrial repolarization record is masked by the larger
QRS complex
Figure 19.16
heart beat electricity
all animations
heart valves
visible heart video clips
heart attack
Cardiac Cycle
Cardiac cycle refers to all events associated
with blood flow through the heart
– Systole – contraction of heart muscle
– Diastole – relaxation of heart muscle
Phases of the Cardiac Cycle
Figure 19.19b
Blood Vessels
Blood is carried in a closed system of vessels that
begins and ends at the heart
 The three major types of vessels are arteries,
capillaries, and veins
 Arteries carry blood away from the heart, veins carry
blood toward the heart
 Capillaries contact tissue cells and directly serve
cellular needs
Generalized Structure of Blood
Arteries and veins are composed of three tunics –
tunica interna, tunica media, and tunica externa
 Capillaries are composed of endothelium with sparse
basal lamina
 Lumen – central blood-containing space surrounded by
Generalized Structure of Blood
Figure 20.1b
Tunica interna (tunica intima)
– Endothelial layer that lines the lumen of all vessels
– In vessels larger than 1 mm, a subendothelial connective
tissue basement membrane is present
Tunica media
– Smooth muscle and elastic fiber layer, regulated by
sympathetic nervous system
– Controls vasoconstriction/vasodilation of vessels
Tunica externa (tunica adventitia)
– Collagen fibers that protect and reinforce vessels
– Larger vessels contain vasa vasorum
Capillary Beds
Figure 20.4a
Capillary Beds
Figure 20.4b
Blood Pressure (BP)
Force per unit area exerted on the wall of a
blood vessel by its contained blood
– Expressed in terms of millimeters of mercury (mm
– Measured in reference to systemic arterial BP in
large arteries near the heart
The differences in BP within the vascular system
provide the driving force that keeps blood
moving from higher to lower pressure areas
Systemic Blood Pressure
Figure 20.5
Measuring Blood Pressure
Systemic arterial BP is measured indirectly with
the auscultatory method
– A sphygmomanometer is placed on the arm superior
to the elbow
Pressure is increased in the cuff until it is greater
than systolic pressure in the brachial artery
Pressure is released slowly and the examiner listens
with a stethoscope
The first sounds heard is recorded as the systolic
The pressure when sound disappears is recorded as
the diastolic pressure
Alterations in Blood Pressure
Hypotension – low BP in which systolic pressure
is below 100 mm Hg
 Hypertension – condition of sustained elevated
arterial pressure of 140/90 or higher
– Transient elevations are normal and can be caused by
fever, physical exertion, and emotional upset
– Chronic elevation is a major cause of heart failure,
vascular disease, renal failure, and stroke

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