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Chapter 22
*Lecture Outline
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Chapter 22 Outline• Overview of the Cardiovascular System• Anatomy of the Heart• Coronary Circulation• How the Heart Beats: Electrical Properties of
Cardiac Tissue• Innervation of the Heart• Tying It All Together: The Cardiac Cycle• Aging and the Heart• Development of the Heart
Overview of the Cardiovascular System
• The heart propels blood to and from most body tissues via two basic types of blood vessels called arteries and veins.
• Arteries are defined as blood vessels that carry blood away from the heart.
• Veins are defined as blood vessels that carry blood back to the heart.
• The arteries and veins entering and leaving the heart are called great vessels.
General Characteristics and Functions of the Heart
• Blood flow through the heart is unidirectional because of four valves within the heart.
• The heart is functionally two side-by-side pumps that work at the same rate and pump the same volume of blood.– One pump directs blood to the lungs.– One pump directs blood to most body tissues.
General Characteristics and Functions of the Heart
• The heart generates blood pressure through alternate cycles of the heart wall’s contraction and relaxation.
• Blood pressure is the force of the blood pushing against the inside walls of blood vessels.
• A minimum blood pressure is essential to circulate blood throughout the body.
Pulmonary and Systemic Circulations
The cardiovascular system consists of two circulations:1. Pulmonary—right side of the heart and the pulmonary arteries and veins; conveys blood to the lungs and back to the left side of the heart2. Systemic—left side of the heart and arteries and veins; conveys blood to most body tissues and back to the right side of the heart
Position of the Heart
• Slightly left of midline deep to the sternum in a compartment of the thorax known as the mediastinum
Figure 22.2
Position of the Heart
• During development, the heart rotates such that the right side or right border (primarily formed by the right atrium and ventricle) is located more anteriorly.
• The left side or left border (primarily formed by the left atrium and ventricle) is located more posteriorly.
Position of the Heart
• The posterosuperior surface of the heart is mainly the left atrium and is called the base of the heart.
• The superior border is formed by the great arterial vessels and the superior vena cava.
• The inferior conical end is called the apex.• The inferior border is formed by the right
ventricle.
Pericardium• The heart is enclosed within a tough sac
called the pericardium• Restricts heart movements so that it moves only slightly within the thorax
Figure 22.2
Pericardium
Composed of two parts:1. Fibrous pericardium—outer covering of
tough, dense connective tissue2. Serous pericardium—composed of two
layers:• parietal layer—lines the inner surface of the
fibrous pericardium• visceral layer (epicardium)—covers the outer
surface of the heart– the small space between the parietal and visceral layers is
called the pericardial cavity
Anatomy of the Heart Wall
The heart wall consists of three distinctive layers (from superficial to deep):1. Epicardium—consists of the visceral layer of the serous pericardium and areolar connective tissue2. Myocardium—cardiac muscle; thickest of the three layers3. Endocardium—internal surface of the heart chambers and external surface of the heart valves
External Heart Anatomy
• Composed of four hollow chambers: two smaller and superior atria (sing., atrium) and two larger inferior ventricles
• The anteroinferior borders of the atria form a muscular extension called the auricle
• The atria and ventricles are separated from each other by a relatively deep groove called the coronary sulcus
• The anterior interventricular sulcus and posterior interventricular sulcus are located between the right and left ventricles and run from the coronary sulcus toward the apex of the heart
Internal Heart Anatomy:Chambers and Valves
The heart possesses four chambers:1. Right atrium2. Right ventricle3. Left atrium4. Left ventricle
The heart also possesses four valves:1. Right atrioventricular (tricuspid)2. Pulmonary semilunar3. Left atrioventricular (bicuspid or mitral)4. Aortic semilunar
Right Atrium
Receives venous blood from heart, the muscles, and systemic circulation; three veins drain into the right atrium:
1. Superior vena cava
2. Inferior vena cava
3. Coronary sinus
Separating the right atrium from the right ventricle is the right atrioventricular valve (tricuspid valve)
Right Atrium
Figure 22.6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ascending aorta
Right pulmonary artery
Right pulmonary veins
Right atrium
Right auricle
Right atrioventricular valve
Right atrioventricular valve
Chordae tendineae
Papillary muscle
Right ventricle
Ascending aorta
Right auricle
Right atrium
Fossa ovalis
Pectinate muscle
Papillary muscle
Trabeculae carneae
Interventricular septum
Pulmonary semilunar valve
Left ventricle
Pulmonary trunk
Ligamentum arteriosum
Aortic arch
Right coronary artery
Right ventricle
Chordae tendineae
Left pulmonary artery
Ligamentum arteriosum
Pulmonary trunk
Left pulmonary veins
Left atrium
Aortic semilunar valve
Left atrioventricular valve
Left ventricle
Septomarginal trabecula
Trabeculae carneae
Interventricular septum
Aortic arch
Descending aorta
Coronal section, anterior view
Interatrial septum
Superior vena cava
Fossa ovalis
Interatrial septumOpening for coronary sinus
Opening for inferiorvena cava
Inferior vena cava
Superior vena cava
Opening for inferiorvena cava
Pulmonary semilunarvalve
© The McGraw- Hill Companies, Inc./Photo and Dissection by Christine Eckel
Right Atrium
• Deoxygenated venous blood flows from the right atrium to the right ventricle through the right atrioventricular valve.
• The right atrioventricular valve is forced closed when the right ventricle begins to contract, preventing blood backflow into the right atrium.
Right Ventricle
• Receives deoxygenated venous blood from the right atrium
• An interventricular septum forms a thick wall between the right and left ventricles
• The inner wall of each ventricle displays large, irregular muscular ridges called trabeculae carneae
Right Ventricle
Figure 22.6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ascending aorta
Right pulmonary artery
Right pulmonary veins
Right atrium
Right auricle
Right atrioventricular valve
Right atrioventricular valve
Chordae tendineae
Papillary muscle
Right ventricle
Ascending aorta
Right auricle
Right atrium
Fossa ovalis
Pectinate muscle
Papillary muscle
Trabeculae carneae
Interventricular septum
Pulmonary semilunar valve
Left ventricle
Pulmonary trunk
Ligamentum arteriosum
Aortic arch
Right coronary artery
Right ventricle
Chordae tendineae
Left pulmonary artery
Ligamentum arteriosum
Pulmonary trunk
Left pulmonary veins
Left atrium
Aortic semilunar valve
Left atrioventricular valve
Left ventricle
Septomarginal trabecula
Trabeculae carneae
Interventricular septum
Aortic arch
Descending aorta
Coronal section, anterior view
Interatrial septum
Superior vena cava
Fossa ovalis
Interatrial septumOpening for coronary sinus
Opening for inferiorvena cava
Inferior vena cava
Superior vena cava
Opening for inferiorvena cava
Pulmonary semilunarvalve
© The McGraw- Hill Companies, Inc./Photo and Dissection by Christine Eckel
Right Ventricle
• There are typically three cone-shaped muscle projections inside the right ventricle called papillary muscles.
• The papillary muscles anchor thin strands of strong connective tissue made up of collagen fibers called chordae tendineae.
• The chordae tendineae attach to three cusps of the (tricuspid) right atrioventricular valve.
• Cusps are triangular flaps that hang down into the ventricle.
• The chordae tendineae prevent the cusps from prolapsing into the right atrium when the right ventricle contracts.
Right Ventricle
Figure 22.6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ascending aorta
Right pulmonary artery
Right pulmonary veins
Right atrium
Right auricle
Right atrioventricular valve
Right atrioventricular valve
Chordae tendineae
Papillary muscle
Right ventricle
Ascending aorta
Right auricle
Right atrium
Fossa ovalis
Pectinate muscle
Papillary muscle
Trabeculae carneae
Interventricular septum
Pulmonary semilunar valve
Left ventricle
Pulmonary trunk
Ligamentum arteriosum
Aortic arch
Right coronary artery
Right ventricle
Chordae tendineae
Left pulmonary artery
Ligamentum arteriosum
Pulmonary trunk
Left pulmonary veins
Left atrium
Aortic semilunar valve
Left atrioventricular valve
Left ventricle
Septomarginal trabecula
Trabeculae carneae
Interventricular septum
Aortic arch
Descending aorta
Coronal section, anterior view
Interatrial septum
Superior vena cava
Fossa ovalis
Interatrial septumOpening for coronary sinus
Opening for inferiorvena cava
Inferior vena cava
Superior vena cava
Opening for inferiorvena cava
Pulmonary semilunarvalve
© The McGraw- Hill Companies, Inc./Photo and Dissection by Christine Eckel
Right Ventricle
• At the superior end or roof of the ventricle is a smooth area called the conus arteriosus.
• Beyond the conus arteriosus is the pulmonary semilunar valve, which marks the end of the ventricle and the beginning of the pulmonary trunk.
Semilunar Valves
• Two of them: pulmonary and aortic• Located in the roof of right and left ventricles,
respectively• Each valve is composed of three thin, half-
moon-shaped, pocketlike semilunar cusps• When ventricles contract, blood pushes cusps
against the arterial trunks• When ventricles relax, some blood flows back
toward the ventricles, enters the pockets of the cusps and forces them toward midline, thus closing the valve
Left Atrium
• Oxygenated blood from the lungs travels through the pulmonary veins to the left atrium.
• The left atrium is separated from the left ventricle by the left atrioventricular valve, which is also referred to as the bicuspid or mitral valve.
• This valve only has two triangular cusps.• This valve is forced shut when the left ventricle
contracts in a similar fashion to the closing of the right atrioventricular valve.
Left Ventricle
• The wall is typically three times thicker than the right ventricular wall.
Figure 22.8
Left Ventricle
• The left ventricle has to pump blood to the entire body, except for the lungs, and therefore has to generate a greater blood pressure.
• At the superior end or roof of the left ventricle is the aortic semilunar valve, which marks the end of the left ventricle and the beginning of the aorta.
Coronary Circulation
• The right and left coronary arteries travel within the coronary sulcus and supply the heart wall muscle with oxygen and nutrients.
• The coronary arteries are the only branches given off by the ascending aorta just superior to the aortic semilunar valve.
Right Coronary Artery
Branches into two arteries:
1. Marginal artery—supplies the right border of the heart
2. Posterior interventricular artery—supplies the posterior surface of the left and right ventricles
Left Coronary Artery
Branches into two arteries:
1. Anterior interventricular artery—also called the left anterior descending artery, supplies the anterior surface of both ventricles and most of the interventricular septum
2. Circumflex artery—supplies the left atrium and ventricle
Coronary Veins
Venous return of blood from the heart wall muscle occurs through three major veins:1. Great cardiac vein—runs alongside the anterior interventricular artery2. Middle cardiac vein—runs alongside the posterior interventricular artery3. Small cardiac vein—travels close to the marginal artery
All three of the above veins drain into a large vein called the coronary sinus that drains into the right atrium.
Conducting System of the Heart
• The myocardium is composed of cardiac muscle fibers.
• Cardiac muscle fibers contract as a single unit because they are all connected with low resistance cell-to-cell junctions called gap junctions.
• Gap junctions comprise the intercalated discs shared by adjacent cardiac muscle fibers.
• Therefore, an electrical impulse is distributed immediately and spontaneously throughout the myocardium.
Structure of Cardiac Muscle
Figure 22.10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nucleus
Sarcolemma
Mitochondrion
Myofibrils
StriationsIntercalated discs
Intercalated disc Intercalated disc
Sarcolemma
Desmosome
Gap junction
Mitochondrion
Cardiac muscle cell
Nucleus
(c) Longitudinal section of cardiac muscle
(b) Cardiac muscle cell, longitudinal view
(a) Cross section of cardiac muscle cell
LM 1000x
Openings oftransverse tubules
Sarcoplasmicreticulum
Transversetubule
Sarcomere
Z disc Z discH zone
M lineI band I band
A band
c © Dennis Drenner/Visuals Unlimited
Conducting System of the Heart
• The heart exhibits autorhythmicity, which means it is capable of initiating its own heartbeat independent of external nerves.
• The electrical impulse that initiates the heartbeat comes from specialized cardiac muscle cells called the sinoatrial (SA) node or the pacemaker.
• The SA node is located on the posterior wall of the right atrium adjacent to the opening of the superior vena cava.
• The SA node generates 70–80 impulses per minute under parasympathetic control.
Conducting System of the Heart
• Impulses from the SA node travel to the left atrium and the atrioventricular (AV) node located in the floor of the right atrium.
• Electrical activity then leaves the AV node into the atrioventricular (AV) bundle (bundle of His), which extends into the interventricular septum.
• Once within the septum, the AV bundle divides into left and right bundles.
Conducting System of the Heart
• These bundles pass the impulse to conduction cells called Purkinje fibers that begin at the apex of the heart.
• The Purkinje fibers spread the impulse superiorly from the apex to all of the ventricular myocardium.
Conducting System of the Heart
Figure 22.11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 2
3 4 5
Superior vena cava
Sinoatrial node (pacemaker)Internodal pathway
Atrioventricular node
Right bundle
Left bundlesPurkinje fibers
Purkinje fibers
Left atriumRight atrium
Purkinje fibers
Atrioventricular bundle(bundle of His)
Muscle impulse is generated at the sinoatrial node. It spreads throughout the atria andto the atrioventricular node by the internodal pathway.
Atrioventricular node cells delay themuscle impulse as it passes to theatrioventricular bundle.
Atrioventricularbundle
InternodalpathwayAtrioventricularnodeInterventricular
septum
Atrioventricularbundle
Left and rightbundle branches
Interventricularseptum
The atrioventricular bundle (bundle of His) conducts the muscle impulseinto the interventricular septum.
Within the interventricular septum, theright and left bundles split from theatrioventricular bundle.
The muscle impulse is delivered to Purkinjefibers in each ventricle and distributedthroughout the ventricular myocardium.
Innervation of the Heart
• The heart, like most other organs, is innervated by both the sympathetic and parasympathetic divisions of the autonomic nervous system.
• The anatomical components of both divisions make up the coronary plexus.
• Autonomic innervation does not initiate a heartbeat, but it can increase or decrease the rate of the heartbeat.
Sympathetic Innervation
• Starts with neurons located in T1–T5 segments of the spinal cord
• Preganglionic axons enter the sympathetic trunk and synapse on ganglionic neurons.
• Postganglionic axons project from all three cervical ganglia and travel to the heart via cardiac nerves.
• Sympathetic input to the heart increases the rate and force of heart contractions.
Parasympathetic Innervation
• Starts with neurons in the medulla oblongata via the left and right vagus nerves (CN X)
• Decreases heart rate but generally has no effect on force of contraction
Coordinated Sequence of Heart Chamber Contractions
1. SA node generates an impulse.
2. Both atria contract almost simultaneously (systole) while ventricles are relaxing (diastole).
3. Impulse goes to AV node and then to the ventricles.
4. Ventricles contract (systole) while atria relax (diastole).
Ventricular Systole and Diastole
Figure 22.13
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Right ventricle Left ventricleSemilunar valves open
Transverse section
Left ventricle
(a) Ventricular Systole (Contraction)
Atrioventricular valves closed
Aortic arch
Anterior
Posterior
Pulmonarytrunk
Blood flow intopulmonary trunk
Leftatrium
Ventricles contract, forcingsemilunar valves to open andblood to enter the pulmonarytrunk and the ascending aorta.
Ventricular contraction pushesblood against the open AVvalves, causing them to close.Contracting papillary musclesand the chordae tendineaeprevent valve flaps fromeverting into atria.
Blood flow intoascending aorta
Ascendingaorta
Blood flow intoright atrium
Rightatrium
Cusp ofsemilunarvalve
Cusp ofatrioventricularvalve
Blood inventricle
Left AVvalve (closed)
Right AVvalve (closed)
Rightventricle
Pulmonarysemilunarvalve (open)
Aortic semilunarvalve (open)
Ventricular Systole and Diastole
Figure 22.13
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Right ventricle Left ventricleSemilunar valves closed
Right ventricle
Transverse section
Left ventricle
Blood
(b) Ventricular Diastole (Relaxation)
Atrioventricular valves open
Aortic arch
Atrium
Anterior
Posterior
Ventricles relax and fill withblood both passively andthen by atrial contraction asAV valves remain open.
During ventricular relaxation,some blood in the ascendingaorta and pulmonary trunkflows back toward theventricles, filling the semilunarvalve cusps and forcing themto close.
Blood flow intoleft ventricle
Leftatrium
Blood flow intoright atrium
Rightatrium
Blood flow intoright ventricle
Cusps ofsemilunarvalve
Cusp ofatrioventricularvalve
Chordaetendineae
Papillarymuscle
Left AVvalve (open)
Right AVvalve (open)
Aortic semilunarvalve (closed)
Pulmonarysemilunarvalve (closed)
Cardiac Cycle
Figure 22.14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Atria relax
Atria contract
1
Atria relax
2
Atria relax
3
Atria relax
5 4
Phase
Structure
Contract
ContractRelax
Relax
Relax
Relax
Open
Closed
Open
Closed
Closed
Open
Atria
V entricles
A V valves
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Semilunarvalvesopen
AVvalvesclosed
Allvalvesclosed
AVvalvesopen
Ventricles contractVentricles contractVentricles relax
Atrial systoleAtria contract; AV valves are open,semilunar valves are closed
Late ventricular systoleAtria continue to relax; ventricles contract;AV valves remain closed; semilunarvalves are forced open
Early ventricular systoleAtria relax; ventricles begin to contract;AV valves are forced closed (lubbsound); semilunar valves still closed
Lateventricular
diastole
Earlyventricular
diastole
Lateventricular
systole
Earlyventricular
systole
Atrialsystole
Semilunarvalves
Time(seconds)
Semilunarvalves closed
Allvalvesclosed
AVvalvesopen
Early ventricular diastoleAtria and ventricles relax; AV valvesremain closed and semilunar valves close(dupp sound); atria continue passivelyfilling with blood
Late ventricular diastoleAtria and ventricles relax; atria continuepassively filling with blood; AV valvesopen and ventricles begin to passively fill;semilunar valves remain closed
Ventricles relaxVentricles relax
0.0
Blood Flow Through the HeartCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Right atrium
Right atrium
Left atrium
Left atrium
Systemic veins
Blood Flow Through the Heart
Superiorand inferior
venae cavaeRightatrium
Rightatrioventricular
valveRight
ventricle
Pulmonarysemilunar
valve
Pulmonarytrunk andarteries
Gas exchangein the lungs
Gas and nutrientexchange
in peripheraltissues
Systemicarteries
AortaAortic
semilunarvalve
Leftventricle
Leftatrioventricular
valve
PulmonaryveinsLeft
atrium
Right ventricle
Left ventricle
Pulmonary veins
Superior vena cava, inferior venacava, coronary sinus
Ascending aorta (blood entersvessels of systemic circulation)
Left ventricle
Pulmonary trunk (blood entersvessels of pulmonary circulation)
Right ventricle
Aortic semilunar valve
Left AV valve
Pulmonary semilunar valve
Right AV valve
Chamber of the Heart Receives Blood From Sends Blood To Valves Through Which BloodFlows
Table 22.3