Chapter 20The Heart
An Introduction to the Cardiovascular System
• The Pulmonary Circuit
• Carries blood to and from gas exchange surfaces of lungs
• The Systemic Circuit
• Carries blood to and from the body
• Blood alternates between pulmonary circuit and systemic circuit
An Introduction to the Cardiovascular System
• Three Types of Blood Vessels
1. Arteries
• Carry blood away from heart
2. Veins
• Carry blood to heart
3. Capillaries
• Networks between arteries and veins
An Introduction to the Cardiovascular System
• Capillaries
• Also called exchange vessels
• Exchange materials between blood and tissues
• Materials include dissolved gases, nutrients, waste products
An Introduction to the Cardiovascular System
• Four Chambers of the Heart
1. Right atrium
• Collects blood from systemic circuit
2. Right ventricle
• Pumps blood to pulmonary circuit
3. Left atrium
• Collects blood from pulmonary circuit
4. Left ventricle
• Pumps blood to systemic circuit
20-1 Anatomy of the Heart
• The Heart
• Great veins and arteries at the base
• Pointed tip is apex
• Surrounded by pericardial sac
• Sits between two pleural cavities in the mediastinum
20-1 Anatomy of the Heart
• The Pericardium
• Double lining of the pericardial cavity
• Visceral pericardium
• Inner layer of pericardium
• Parietal pericardium
• Outer layer
• Forms inner layer of pericardial sac
20-1 Anatomy of the Heart
• The Pericardium
• Pericardial cavity
• Is between parietal and visceral layers
• Contains pericardial fluid
• Pericardial sac
• Fibrous tissue
• Surrounds and stabilizes heart
20-1 Anatomy of the Heart
• Superficial Anatomy of the Heart
• Atria
• Thin-walled
• Expandable outer auricle (atrial appendage)
20-1 Anatomy of the Heart
• Superficial Anatomy of the Heart
• Sulci
• Coronary sulcus divides atria and ventricles
• Anterior interventricular sulcus and posterior interventricular sulcus
• Separate left and right ventricles
• Contain blood vessels of cardiac muscle
20-1 Anatomy of the Heart
• The Heart Wall
1. Epicardium
2. Myocardium
3. Endocardium
20-1 Anatomy of the Heart
• Epicardium (Outer Layer)
• Visceral pericardium
• Covers the heart
20-1 Anatomy of the Heart
• Myocardium (Middle Layer)
• Muscular wall of the heart
• Concentric layers of cardiac muscle tissue
• Atrial myocardium wraps around great vessels
• Two divisions of ventricular myocardium
• Endocardium (Inner Layer)
• Simple squamous epithelium
20-1 Anatomy of the Heart
• Cardiac Muscle Tissue
• Intercalated discs
• Interconnect cardiac muscle cells
• Secured by desmosomes
• Linked by gap junctions
• Convey force of contraction
• Propagate action potentials
20-1 Anatomy of the Heart
• Characteristics of Cardiac Muscle Cells
1. Small size
2. Single, central nucleus
3. Branching interconnections between cells
4. Intercalated discs
20-1 Anatomy of the Heart
• Internal Anatomy and Organization
• Interatrial septum separates atria
• Interventricular septum separates ventricles
20-1 Anatomy of the Heart
• Internal Anatomy and Organization
• Atrioventricular (AV) valves
• Connect right atrium to right ventricle and left atrium to left ventricle
• Are folds of fibrous tissue that extend into openings between atria and ventricles
• Permit blood flow in one direction
• From atria to ventricles
20-1 Anatomy of the Heart
• The Right Atrium
• Superior vena cava
• Receives blood from head, neck, upper limbs, and chest
• Inferior vena cava
• Receives blood from trunk, viscera, and lower limbs
• Coronary sinus
• Cardiac veins return blood to coronary sinus
• Coronary sinus opens into right atrium
20-1 Anatomy of the Heart
• The Right Atrium
• Foramen ovale
• Before birth, is an opening through interatrial septum
• Connects the two atria
• Seals off at birth, forming fossa ovalis
20-1 Anatomy of the Heart
• The Right Atrium
• Pectinate muscles
• Contain prominent muscular ridges
• On anterior atrial wall and inner surfaces of right auricle
20-1 Anatomy of the Heart
• The Right Ventricle
• Free edges attach to chordae tendineae from papillary muscles of ventricle
• Prevent valve from opening backward
• Right atrioventricular (AV) valve
• Also called tricuspid valve
• Opening from right atrium to right ventricle
• Has three cusps
• Prevents backflow
20-1 Anatomy of the Heart
• The Right Ventricle
• Trabeculae carneae
• Muscular ridges on internal surface of right (and left) ventricle
• Includes moderator band
• Ridge contains part of conducting system
• Coordinates contractions of cardiac muscle cells
20-1 Anatomy of the Heart
• The Pulmonary Circuit
• Conus arteriosus (superior end of right ventricle) leads to pulmonary trunk
• Pulmonary trunk divides into left and right pulmonary arteries
• Blood flows from right ventricle to pulmonary trunk through pulmonary valve
• Pulmonary valve has three semilunar cusps
20-1 Anatomy of the Heart
• The Left Atrium
• Blood gathers into left and right pulmonary veins
• Pulmonary veins deliver to left atrium
• Blood from left atrium passes to left ventricle through left atrioventricular (AV) valve
• A two-cusped bicuspid valve or mitral valve
20-1 Anatomy of the Heart
• The Left Ventricle
• Holds same volume as right ventricle
• Is larger; muscle is thicker and more powerful
• Similar internally to right ventricle but does not have moderator band
20-1 Anatomy of the Heart
• The Left Ventricle
• Systemic circulation
• Blood leaves left ventricle through aortic valve into ascending aorta
• Ascending aorta turns (aortic arch) and becomes descending aorta
20-1 Anatomy of the Heart
• Structural Differences between the Left and Right Ventricles
• Right ventricle wall is thinner, develops less pressure than left ventricle
• Right ventricle is pouch-shaped, left ventricle is round
20-1 Anatomy of the Heart
• The Heart Valves
• Two pairs of one-way valves prevent backflow during contraction
• Atrioventricular (AV) valves
• Between atria and ventricles
• Blood pressure closes valve cusps during ventricular contraction
• Papillary muscles tense chordae tendineae to prevent valves from swinging into atria
20-1 Anatomy of the Heart
• The Heart Valves
• Semilunar valves
• Pulmonary and aortic tricuspid valves
• Prevent backflow from pulmonary trunk and aorta into ventricles
• Have no muscular support
• Three cusps support like tripod
20-1 Anatomy of the Heart
• Aortic Sinuses
• At base of ascending aorta
• Sacs that prevent valve cusps from sticking to aorta
• Origin of right and left coronary arteries
20-1 Anatomy of the Heart
• Connective Tissues and the Cardiac Skeleton
• Connective Tissue Fibers
1. Physically support cardiac muscle fibers
2. Distribute forces of contraction
3. Add strength and prevent overexpansion of heart
4. Provide elasticity that helps return heart to original size and shape after contraction
20-1 Anatomy of the Heart
• The Cardiac Skeleton
• Four bands around heart valves and bases of pulmonary trunk and aorta
• Stabilize valves
• Electrically insulate ventricular cells from atrial cells
20-1 Anatomy of the Heart
• The Blood Supply to the Heart
• = Coronary circulation
• Supplies blood to muscle tissue of heart
• Coronary arteries and cardiac veins
20-1 Anatomy of the Heart
• The Coronary Arteries
• Left and right
• Originate at aortic sinuses
• High blood pressure, elastic rebound forces blood through coronary arteries between contractions
20-1 Anatomy of the Heart
• Right Coronary Artery
• Supplies blood to:
• Right atrium
• Portions of both ventricles
• Cells of sinoatrial (SA) and atrioventricular nodes
• Marginal arteries (surface of right ventricle)
• Posterior interventricular artery
20-1 Anatomy of the Heart
• Left Coronary Artery
• Supplies blood to:
• Left ventricle
• Left atrium
• Interventricular septum
20-1 Anatomy of the Heart
• Two Main Branches of Left Coronary Artery
1. Circumflex artery
2. Anterior interventricular artery
• Arterial Anastomoses
• Interconnect anterior and posterior interventricular arteries
• Stabilize blood supply to cardiac muscle
20-1 Anatomy of the Heart
• The Cardiac Veins
• Great cardiac vein
• Drains blood from area of anterior interventricular artery into coronary sinus
• Anterior cardiac veins
• Empty into right atrium
• Posterior cardiac vein, middle cardiac vein, and small cardiac vein
• Empty into great cardiac vein or coronary sinus
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Coronary artery disease (CAD)
• Areas of partial or complete blockage of coronary circulation
• Cardiac muscle cells need a constant supply of oxygen and nutrients
• Reduction in blood flow to heart muscle produces a corresponding reduction in cardiac performance
• Reduced circulatory supply, coronary ischemia, results from partial or complete blockage of coronary arteries
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Usual cause is formation of a fatty deposit, or atherosclerotic plaque, in the wall of a coronary vessel
• The plaque, or an associated thrombus (clot), then narrows the passageway and reduces blood flow
• Spasms in smooth muscles of vessel wall can further decrease or stop blood flow
• One of the first symptoms of CAD is commonly angina pectoris
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Angina Pectoris
• In its most common form, a temporary ischemia develops when the workload of the heart increases
• Although the individual may feel comfortable at rest, exertion or emotional stress can produce a sensation of pressure, chest constriction, and pain that may radiate from the sternal area to the arms, back, and neck
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Myocardial infarction (MI), or heart attack
• Part of the coronary circulation becomes blocked, and cardiac muscle cells die from lack of oxygen
• The death of affected tissue creates a nonfunctional area known as an infarct
• Heart attacks most commonly result from severe coronary artery disease (CAD)
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Myocardial infarction (MI), or heart attack
• Consequences depend on the site and nature of the circulatory blockage
• If it occurs near the start of one of the coronary arteries:
• The damage will be widespread and the heart may stop beating
• If the blockage involves one of the smaller arterial branches:
• The individual may survive the immediate crisis but may have many complications such as reduced contractility and cardiac arrhythmias
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Myocardial infarction (MI), or heart attack
• A crisis often develops as a result of thrombus formation at a plaque (the most common cause of an MI), a condition called coronary thrombosis
• A vessel already narrowed by plaque formation may also become blocked by a sudden spasm in the smooth muscles of the vascular wall
• Individuals having an MI experience intense pain, similar to that felt in angina, but persisting even at rest
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Myocardial infarction (MI), or heart attack
• Pain does not always accompany a heart attack, therefore, the condition may go undiagnosed and may not be treated before a fatal MI occurs
• A myocardial infarction can usually be diagnosed with an ECG and blood studies
• Damaged myocardial cells release enzymes into the circulation, and these elevated enzymes can be measured in diagnostic blood tests
• The enzymes include:
• Cardiac troponin T,
• Cardiac troponin I,
• A special form of creatinine phosphokinase, CK-MB
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• About 25% of MI patients die before obtaining medical assistance
• 65% of MI deaths among those under age 50 occur within an hour after the initial infarction
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Risk Factor Modification
• Stop smoking
• High blood pressure treatment
• Dietary modification to lower cholesterol and promote weight loss
• Stress reduction
• Increased physical activity (where appropriate)
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Drug Treatment
• Drugs that reduce coagulation and therefore the risk of thrombosis, such as aspirin and coumadin
• Drugs that block sympathetic stimulation (propranolol or metoprolol)
• Drugs that cause vasodilation, such as nitroglycerin
• Drugs that block calcium movement into the cardiac and vascular smooth muscle cells (calcium channel blockers)
• In a myocardial infarction, drugs to relieve pain, fibrinolytic agents to help dissolve clots, and oxygen
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Noninvasive Surgery
• Atherectomy
• Blockage by a single, soft plaque may be reduced with the aid of a long, slender catheter inserted into a coronary artery to the plaque
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Noninvasive Surgery
• Balloon angioplasty
• The tip of the catheter contains an inflatable balloon
• Once in position, the balloon is inflated, pressing the plaque against the vessel walls
• Because plaques commonly redevelop after angioplasty, a fine tubular wire mesh called a stent may be inserted into the vessel, holding it open
20-1 Anatomy of the Heart
• Heart Disease - Coronary Artery Disease
• Treatment of CAD and Myocardial Infarction
• Coronary Artery Bypass Surgery (CABG)
• In a coronary artery bypass graft, a small section is removed from either a small artery or a peripheral vein and is used to create a detour around the obstructed portion of a coronary artery