19 PART 1
The Heart
The Heart
•The heart is a muscular double pump
•Two functions
•Pulmonary circuit: Right side receives oxygen-poor blood from the body and pumps it to the lungs
•Systemic circuit: Left side receives oxygenated blood from lungs and pumps throughout the body
The Heart
•Atria
•Receive blood from the pulmonary and systemic circuits
•Ventricles
•The pumping chambers of the heart
Location and Orientation within the Thorax
•Heart
•Healthy heart typically weighs 250–350 grams
•Largest organ of the mediastinum
•Located between the lungs
•Apex lies to the left of the midline
•Base is the broad posterior surface
Four “Corners” of the Heart
•Superior right
•At costal cartilage of third rib and sternum
•Inferior right
•At costal cartilage of sixth rib lateral to the sternum
•Superior left
•At costal cartilage of second rib lateral to the sternum
•Inferior left
•Lies in the fifth intercostal space at the midclavicular line
Structure of the Heart—Coverings
•Pericardium—two primary layers
•Fibrouspericardium
•Strong layer of dense connective tissue
•Serous pericardium
•Formed from two layers
•Parietal layer of the serous pericardium
•Visceral layer of the serous pericardium
Layers of the Heart Wall
•Epicardium
•Visceral layer of the serous pericardium
•Myocardium
•Consists of cardiac muscle
•Muscle arranged in circular and spiral patterns
•Endocardium
•Endothelium resting on a layer of connective tissue
•Lines the internal walls of the heart
Heart Chambers
•Right and left atria
•Superior chambers
•Right and left ventricles
•Inferior chambers
•Internal divisions
•Interventricular septa
•Interatrial septa
Heart Chambers
•External markings
•Coronary sulcus
•Anterior interventricular sulcus
•Posterior interventricular sulcus
Right Atrium
•Forms right border of heart
•Receives oxygen-poor blood from systemic circuit through these vessels:
•Superior vena cava
•Inferior vena cava
•Coronary sinus
Right Atrium
•Pectinate muscles
•Ridges inside anterior of right atrium
•Crista terminalis
•Landmark used to locate veins entering right atrium
•Fossa ovalis
•Depression in interatrial septum
•Remnant of foramen ovale
Right Ventricle
•Receives blood from right atrium through the right atrioventricular valve (tricuspid valve)
•Pumps blood into pulmonary circuit the pulmonary trunk
Right Ventricle
•Internal walls of right ventricle
•Trabeculae carneae
•Papillary muscles
•Chordae tendineae
•Pulmonary semilunar valve (pulmonary valve)
•Located at opening of right ventricle and pulmonary trunk
Left Atrium
•Makes up heart’s posterior surface
•Receives oxygen-rich blood from lungs through pulmonary veins
•Opens into the left ventricle through
•Left atrioventricular valve (bicuspid valve)
•Mitral valve is another name for the left AV valve
Left Ventricle
•Forms apex of the heart
•Internal walls of left ventricle
•Trabeculae carneae
•Papillary muscles
•Chordae tendineae
•Pumps blood through systemic circuit via
•Aortic semilunar valve (aortic valve)
Heart Valves—Valve Structure
•Each valve composed of
•Endocardium with connective tissue core
•Atrioventricular (AV) valves
•Between atria and ventricles
•Right AV valve tricuspid valve
•Left AV valve bicuspid (mitral) valve
•Aortic and pulmonary valves
•At junction of ventricles and great arteries
Cardiac Skeleton
•Surrounds all four valves
•Composed of dense connective tissue
•Functions
• Anchors valve cusps
• Prevents overdilation of valve openings
• Main point of insertion for cardiac muscle
• Blocks direct spread of electrical impulses
Heart Sounds
•“Lub-dup”—sound of valves closing
•First sound: “lub”
•The AV valves closing
•Second sound: “dup”
•The semilunar valvesclosing
Heart Sounds
•Each valve sound is best heard near a different heart corner
•Pulmonary valve—superior left corner
•Aortic valve—superior right corner
•Mitral (bicuspid) valve—at the apex
•Tricuspid valve—inferior right corner
Pathway of Blood Through the Heart
•Beginning with oxygen-poor blood in the superior and inferior venae cavae
•Describe the pathway through
•Pulmonary and systemic circuits
•A blood drop passes through all structures sequentially
•Atria contract together
•Ventricles contract together
Heartbeat
•70–80 beats per minute at rest
•Systole—contraction of a heart chamber
•Diastole—expansion of a heart chamber
•Systole and diastole also refer to
•Stage of heartbeat when ventricles contract and expand
Structure of Heart Wall
•Walls differ in thickness
•Atria—thin walls
•Ventricles—thick walls
•Systemic circuit
•Longer than pulmonary circuit
•Offers greater resistance to blood flow
Structure of Heart Wall
•Left ventricle
•Three times thicker than right ventricle
•Exerts more pumping force
•Flattens right ventricle into a crescent shape
Cardiac Muscle Tissue
•Cardiac muscle tissue forms the myocardium
•Striated, like skeletal muscle
•Contractions pump blood through the heart and into blood vessels
•Contracts by sliding filament mechanism
Cardiac Muscle Tissue
•Cardiac muscle cells
•Short
•Branching
•Have one or two nuclei
•Unlike skeletal muscle, not fused colonies
Cardiac Muscle Tissue
•Cells join at intercalated discs
•Complex junctions
•Form cellular networks
•Cells are separated by delicate endomysium
•Binds adjacent cardiac fibers
•Contains blood vessels and nerves
Cardiac Muscle Tissue
•Intercalated discs—complex junctions
•Adjacent sarcolemmas interlock
•Possess three types of cell junctions
•Desmosomes
•Fasciae adherens—long desmosome-like junctions
•Gap junctions
Cardiac Muscle Tissue
•Triggered to contract by Ca2 entering the sarcoplasm
•Signals sarcoplasmic reticulum to release Ca2 ions
•Ions diffuse into sarcomeres
•Trigger sliding filament mechanism
Cardiac Muscle Tissue
•Not all cardiac cells are innervated
•Will contract in rhythmic manner without innervation
•Inherent rhythmicity
•Is the basis for rhythmic heartbeat
Conducting System
•Cardiac muscle tissue has intrinsic ability to
•Generate and conduct impulses
•Signal these cells to contract rhythmically
•Conducting system
•A series of specialized cardiac muscle cells
•Sinoatrial (SA) node sets the inherent rate of contraction
Conducting System
•From the SA node
•Internodal pathway to the AV node
•AV node to the AV bundle
•AV bundle to the bundle branches
•Bundle branches into the subendocardial conducting network (Purkinje fibers)
Innervation
•Heart rate is set by SA node
•Rate is altered by extrinsic and neural controls
•Visceral sensory fibers
•Parasympathetic fibers
•Nerves pass through cardiac plexus
Innervation
•Parasympathetic fibers
•Branches of vagus nerve
•Decrease heart rate
•Restricted to
•SA node, AV node, coronary arteries
Innervation
•Sympathetic nerves
•Travel to heart from cervical and upper thoracic chain ganglia
•Innervate SA node, AV node, coronary arteries—as parasympathetic
•Also innervate cardiac musculature throughout the heart
•Increase heart rate and strength of contraction
Autonomic Input
•Controlled by cardiac centers in reticular formation of medulla
•Cardioinhibitory center
•Influences parasympathetic neurons
•Cardioacceleratory center
•Influences sympathetic neurons
19 PART 2
The Heart
Blood Supply to the Heart
•Coronary arteries
•Blood supply to the muscular walls and tissues of the heart
•Right coronary artery
•Left coronary artery
•Arise from base of the aorta and run in the coronary sulcus
Blood Supply to the Heart
•Coronary arteries, continued
•Left coronary artery (LCA)
•Branches into anterior interventricular artery and circumflex artery
•Left anterior descending artery (LAD) is the clinical name for anterior interventricular artery
Blood Supply to the Heart
•Coronary arteries, continued
•Right coronary artery (RCA) descends in coronary sulcus
•Branches to form the marginal artery
•Later braches into the posterior interventricular artery
•Clinically called posterior descending artery (PDA)
Cardiac Veins
•Carry deoxygenated blood from the heart wall to the right atrium
•Occupy sulci on the heart’s surface
•Coronary sinus—runs in the posterior part of the coronary sulcus
•Returns majority of venous blood from the heart to the right atrium
•Three tributaries of coronary sinus
•Great cardiac vein, middle cardiac vein, small cardiac vein
Disorders of the Heart
•Coronary artery disease
•Atherosclerosis—fatty deposits
•Angina pectoris—chest pain
•Myocardial infarction—blocked coronary artery
•Heart attack
•Silent ischemia—no pain or warning
Disorders of the Heart
•Heart failure
•Progressive weakening of the heart
•Cannot meet the body’s demands for oxygenated blood
•Congestive heart failure (CHF)
•Heart enlarges
•Pumping efficiency declines
•Pulmonary arterial hypertension
•Enlargement and potential failure of right ventricle
Disorders of the Conduction System
•Arrythmias—variation from normal heart rhythm
•Ventricular fibrillation
•Rapid, random firing of electrical impulses in the ventricles
•Results from crippled conducting system
•Common cause of cardiac arrest
Disorders of the Conductory System
•Arrythmias (continued)
•Atrial fibrillation
•Impulses circle within atrial myocardium, stimulating AV node
•Promotes formation of clots
•Leads to strokes
•Occurs in episodes characterized by
•Anxiety, fatigue, shortness of breath, palpitations
Development of the Heart
•Heart folds into thorax region about day 20–21
•Heart starts pumping about day 22
•Earliest heart chambers are unpaired
•From “tail to head,” the chambers are
•Sinus venosus
•Atrium
•Ventricle
•Bulbus cordis
Development of the Heart
•Sinus venosus—will become
•Smooth-walled part of right atrium, coronary sinus, and SA node
•Also contributes to back wall of left atrium
•Atrium—will become
•Ridged parts of right and left atria
Development of the Heart
•Ventricle—is the strongest pumping chamber
•Gives rise to the left ventricle
•Bulbus cordis
•Bulbus cordis and truncus arteriosus give rise to the pulmonary trunk and first part of aorta
•Bulbus cordis gives rise to the left ventricle
Congenital Heart Defects
•Can be traced to month 2 of development
•Most common defect is ventricular septal defect
•Two basic categories of defect
•Inadequately oxygenated blood reaches body tissues
•Ventricles labor under increased workload
The Heart in Old Age
•Heart usually functions well throughout life
•Regular exercise increases the strength of the heart
•Aerobic exercise can help clear fatty deposits in coronary arteries
The Heart in Old Age
•Age-related changes
• Hardening and thickening of heart valve cusps
• Decline in cardiac reserve
• Fibrosis of cardiac muscle