AP-Ch18 by EVE ROAKE

Chapter

18 The Heart

PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris

Introduction to 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

Introduction to Cardiovascular System   Three Types of Blood Vessels   Arteries   Carry blood away from heart

  Veins   Carry blood to heart

Introduction to Cardiovascular System   Capillaries   Also called exchange vessels   Exchange materials between blood and tissues   Materials include dissolved gases, nutrients, wastes Copyright © 2010 Pearson Education, Inc.

Introduction to Cardiovascular System

Introduction to Cardiovascular System   Four Chambers of the Heart   Right atrium   Collects blood from systemic circuit

  Right ventricle   Pumps blood to pulmonary circuit

  Left atrium   Collects blood from pulmonary circuit

Anatomy of 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

Anatomy of the Heart

Anatomy of the Heart   The Pericardium   Double lining of the pericardial cavity   Parietal pericardium   Outer layer   Forms inner layer of pericardial sac

  Visceral pericardium   Inner layer of pericardium

Anatomy of the Heart   The Pericardium   Pericardial cavity   Is between parietal and visceral layers   Contains pericardial fluid

Anatomy of the Heart

Anatomy of the Heart   Superficial Anatomy of the Heart   Atria   Thin-walled   Expandable outer auricle (atrial appendage)

  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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Anatomy of the Heart   The Heart Wall   Epicardium (outer layer)   Visceral pericardium   Covers 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

Anatomy of the Heart

Figure 18–4 The Heart Wall

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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

Anatomy of the Heart   Characteristics of Cardiac Muscle Cells   Small size   Single, central nucleus   Branching interconnections between cells   Intercalated discs

Anatomy of the Heart

Anatomy of the Heart   Internal Anatomy and Organization   Interatrial septum: separates atria   Interventricular septum: separates ventricles   Atrioventricular (AV) valves   Connect right atrium to right ventricle and left atrium to left ventricle   The fibrous flaps that form bicuspid (2) and tricuspid (3) valves   Permit blood flow in one direction: atria to ventricles The Heart: Valves Copyright © 2010 Pearson Education, Inc.

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

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

Anatomy of the Heart   The Right Atrium   Pectinate muscles   Contain prominent muscular ridges   On anterior atrial wall and inner surfaces of right auricle

Anatomy of the Heart

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 Copyright © 2010 Pearson Education, Inc.

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

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 Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

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   Systemic circulation   Blood leaves left ventricle through aortic valve into ascending aorta   Ascending aorta turns (aortic arch) and becomes descending aorta Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart

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: prevent valves from swinging into atria Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

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

Anatomy of the Heart

Figure 18–8c Valves of the Heart

Anatomy of the Heart   Connective Tissues and the Cardiac (Fibrous) Skeleton   Physically support cardiac muscle fibers   Distribute forces of contraction   Add strength and prevent overexpansion of heart   Elastic fibers return heart to original shape after contraction Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart   The Cardiac (Fibrous) Skeleton   Four bands around heart valves and bases of pulmonary trunk and aorta   Stabilize valves   Electrically insulate ventricular cells from atrial cells

Anatomy of the Heart   The Blood Supply to the Heart = Coronary Circulation   Coronary arteries and cardiac veins   Supplies blood to muscle tissue of heart

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

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 Copyright © 2010 Pearson Education, Inc.

Anatomy of the Heart   Left Coronary Artery   Supplies blood to   Left ventricle   Left atrium   Interventricular septum

Anatomy of the Heart   Two main branches of left coronary artery   Circumflex artery   Anterior interventricular artery

Anatomy of the Heart   The Cardiac Veins   Great cardiac vein   Drains blood from area of anterior interventricular artery into coronary sinus

  Anterior cardiac veins   Empties into right atrium

Anatomy of the Heart

The Conducting System   Heartbeat   A single contraction of the heart   The entire heart contracts in series   First the atria   Then the ventricles

The Conducting System   Two Types of Cardiac Muscle Cells   Conducting system   Controls and coordinates heartbeat

  Contractile cells   Produce contractions that propel blood

The Conducting System   The Cardiac Cycle   Begins with action potential at SA node   Transmitted through conducting system   Produces action potentials in cardiac muscle cells (contractile cells)

  Electrocardiogram (ECG)   Electrical events in the cardiac cycle can be recorded on an electrocardiogram (ECG)

The Conducting System

The Conducting System   A system of specialized cardiac muscle cells   Initiates and distributes electrical impulses that stimulate contraction

The Conducting System   Structures of the Conducting System   Sinoatrial (SA) node - wall of right atrium   Atrioventricular (AV) node - junction between atria and ventricles   Conducting cells - throughout myocardium

The Conducting System   Conducting Cells   Interconnect SA and AV nodes   Distribute stimulus through myocardium   In the atrium   Internodal pathways

The Conducting System   Prepotential   Also called pacemaker potential   Resting potential of conducting cells   Gradually depolarizes toward threshold

  SA node depolarizes first, establishing heart rate

The Conducting System

The Conducting System   Heart Rate   SA node generates 80–100 action potentials per minute   Parasympathetic stimulation slows heart rate   AV node generates 40–60 action potentials per minute

The Conducting System   The Sinoatrial (SA) Node   In posterior wall of right atrium   Contains pacemaker cells   Connected to AV node by internodal pathways   Begins atrial activation (Step 1) Copyright © 2010 Pearson Education, Inc.

The Conducting System

The Conducting System   The Atrioventricular (AV) Node   In floor of right atrium   Receives impulse from SA node (Step 2)   Delays impulse (Step 3)   Atrial contraction begins

The Conducting System

The Conducting System   The AV Bundle   In the septum   Carries impulse to left and right bundle branches   Which conduct to Purkinje fibers (Step 4)

The Conducting System

The Conducting System   Purkinje Fibers   Distribute impulse through ventricles (Step 5)   Atrial contraction is completed   Ventricular contraction begins

The Conducting System

The Conducting System   Abnormal Pacemaker Function   Bradycardia: abnormally slow heart rate   Tachycardia: abnormally fast heart rate   Ectopic pacemaker   Abnormal cells   Generate high rate of action potentials   Bypass conducting system   Disrupt ventricular contractions

The Conducting System   Electrocardiogram (ECG or EKG)   A recording of electrical events in the heart   Obtained by electrodes at specific body locations   Abnormal patterns diagnose damage

The Conducting System   Features of an ECG   P wave   Atria depolarize

  QRS complex   Ventricles depolarize

The Conducting System   Time Intervals Between ECG Waves   P–R interval   From start of atrial depolarization   To start of QRS complex

The Conducting System

The Conducting System   Contractile Cells   Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart   Resting Potential   Of a ventricular cell: about –90 mV   Of an atrial cell: about –80 mV Copyright © 2010 Pearson Education, Inc.

The Conducting System

The Conducting System   Refractory Period   Absolute refractory period   Long   Cardiac muscle cells cannot respond

The Conducting System   Timing of Refractory Periods   Length of cardiac action potential in ventricular cell   250–300 msecs: –  30 times longer than skeletal muscle fiber –  long refractory period prevents summation and tetany

The Conducting System   The Role of Calcium Ions in Cardiac Contractions   Contraction of a cardiac muscle cell is produced by an increase in calcium ion concentration around myofibrils

The Conducting System   The Role of Calcium Ions in Cardiac Contractions   20% of calcium ions required for a contraction   Calcium ions enter plasma membrane during plateau phase

  Arrival of extracellular Ca2+   Triggers release of calcium ion reserves from sarcoplasmic reticulum

The Conducting System   The Role of Calcium Ions in Cardiac Contractions   As slow calcium channels close   Intracellular Ca2+ is absorbed by the SR   Or pumped out of cell

The Conducting System   The Energy for Cardiac Contractions   Aerobic energy of heart   From mitochondrial breakdown of fatty acids and glucose   Oxygen from circulating hemoglobin   Cardiac muscles store oxygen in myoglobin

The Cardiac Cycle   Cardiac cycle = The period between the start of one heartbeat and the beginning of the next   Includes both contraction and relaxation

The Cardiac Cycle   Phases of the Cardiac Cycle   Within any one chamber   Systole (contraction)   Diastole (relaxation)

The Cardiac Cycle

The Cardiac Cycle   Blood Pressure   In any chamber   Rises during systole   Falls during diastole

The Cardiac Cycle   Cardiac Cycle and Heart Rate   At 75 beats per minute   Cardiac cycle lasts about 800 msecs

  When heart rate increases   All phases of cardiac cycle shorten, particularly diastole

The Cardiac Cycle Eight Steps in the Cardiac Cycle 1.  Atrial systole 

Atrial contraction begins



Right and left AV valves are open

2.  Atria eject blood into ventricles 

Filling ventricles

5.  Atrial systole ends 

AV valves close



Ventricles contain maximum blood volume



Known as end-diastolic volume (EDV)

The Cardiac Cycle

The Cardiac Cycle Eight Steps in the Cardiac Cycle 4.  Ventricular systole 

Isovolumetric ventricular contraction



Pressure in ventricles rises



AV valves shut

6.  Ventricular ejection 

Semilunar valves open



Blood flows into pulmonary and aortic trunks



Stroke volume (SV) = 60% of end-diastolic volume

The Cardiac Cycle

The Cardiac Cycle Eight Steps in the Cardiac Cycle 6.  Ventricular pressure falls 

Semilunar valves close



Ventricles contain end-systolic volume (ESV), about 40% of end-diastolic volume

8.  Ventricular diastole 

Ventricular pressure is higher than atrial pressure



All heart valves are closed



Ventricles relax (isovolumetric relaxation)

The Cardiac Cycle

The Cardiac Cycle Eight Steps in the Cardiac Cycle 8.  Atrial pressure is higher than ventricular pressure   AV valves open   Passive atrial filling   Passive ventricular filling   Cardiac cycle ends The Heart: Cardiac Cycle Copyright © 2010 Pearson Education, Inc.

The Cardiac Cycle

The Cardiac Cycle   Heart Sounds   S1   Loud sounds   Produced by AV valves

  S2   Loud sounds   Produced by semilunar valves

The Cardiac Cycle   Heart Murmur   Sounds produced by regurgitation through valves

The Cardiac Cycle

Cardiodynamics   The movement and force generated by cardiac contractions   End-diastolic volume (EDV)   End-systolic volume (ESV)   Stroke volume (SV)   SV = EDV – ESV

  Ejection fraction   The percentage of EDV represented by SV

Cardiodynamics

Cardiodynamics   Factors Affecting Cardiac Output   Cardiac output   Adjusted by changes in heart rate or stroke volume

  Heart rate   Adjusted by autonomic nervous system or hormones

  Stroke volume   Adjusted by changing EDV or ESV

Cardiodynamics

Cardiodynamics   Factors Affecting the Heart Rate   Autonomic innervation   Cardiac plexuses: innervate heart   Vagus nerves (X): carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus   Cardiac centers of medulla oblongata: –  cardioacceleratory center controls sympathetic neurons (increases heart rate) –  cardioinhibitory center controls parasympathetic neurons (slows heart rate) Copyright © 2010 Pearson Education, Inc.

Cardiodynamics   Autonomic Innervation   Cardiac reflexes   Cardiac centers monitor: –  blood pressure (baroreceptors) –  arterial oxygen and carbon dioxide levels (chemoreceptors)

  Cardiac centers adjust cardiac activity   Autonomic tone   Dual innervation maintains resting tone by releasing ACh and NE   Fine adjustments meet needs of other systems Copyright © 2010 Pearson Education, Inc.

Cardiodynamics

Cardiodynamics   Effects on the SA Node   Sympathetic and parasympathetic stimulation   Greatest at SA node (heart rate)

  Membrane potential of pacemaker cells   Lower than other cardiac cells

  Rate of spontaneous depolarization depends on   Resting membrane potential   Rate of depolarization

  ACh (parasympathetic stimulation)   Slows the heart

Cardiodynamics

Cardiodynamics   Atrial Reflex   Also called Bainbridge reflex   Adjusts heart rate in response to venous return   Stretch receptors in right atrium   Trigger increase in heart rate   Through increased sympathetic activity Copyright © 2010 Pearson Education, Inc.

Cardiodynamics   Hormonal Effects on Heart Rate   Increase heart rate (by sympathetic stimulation of SA node)   Epinephrine (E)   Norepinephrine (NE)   Thyroid hormone

Cardiodynamics   Factors Affecting the Stroke Volume   The EDV: amount of blood a ventricle contains at the end of diastole   Filling time: –  duration of ventricular diastole

  Venous return: –  rate of blood flow during ventricular diastole

Cardiodynamics   Preload   The degree of ventricular stretching during ventricular diastole   Directly proportional to EDV   Affects ability of muscle cells to produce tension

Cardiodynamics   The EDV and Stroke Volume   At rest   EDV is low   Myocardium stretches less   Stroke volume is low

Cardiodynamics   The Frank–Starling Principle   As EDV increases, stroke volume increases

  Physical Limits   Ventricular expansion is limited by   Myocardial connective tissue   The cardiac (fibrous) skeleton   The pericardial sac

Cardiodynamics   End-Systolic Volume (ESV)   The amount of blood that remains in the ventricle at the end of ventricular systole is the ESV

Cardiodynamics   Three Factors That Affect ESV   Preload   Ventricular stretching during diastole

  Contractility   Force produced during contraction, at a given preload

  Afterload   Tension the ventricle produces to open the semilunar valve and eject blood

Cardiodynamics   Contractility   Is affected by   Autonomic activity   Hormones

Cardiodynamics   Effects of Autonomic Activity on Contractility   Sympathetic stimulation   NE released by postganglionic fibers of cardiac nerves   Epinephrine and NE released by suprarenal (adrenal) medullae   Causes ventricles to contract with more force   Increases ejection fraction and decreases ESV

Cardiodynamics   Effects of Autonomic Activity on Contractility   Parasympathetic activity   Acetylcholine released by vagus nerves   Reduces force of cardiac contractions

Cardiodynamics   Hormones   Many hormones affect heart contraction   Pharmaceutical drugs mimic hormone actions   Stimulate or block beta receptors   Affect calcium ions (e.g., calcium channel blockers)

Cardiodynamics   Afterload   Is increased by any factor that restricts arterial blood flow   As afterload increases, stroke volume decreases

Cardiodynamics

Cardiodynamics   Heart Rate Control Factors   Autonomic nervous system   Sympathetic and parasympathetic

  Circulating hormones   Venous return and stretch receptors

Cardiodynamics   Stroke Volume Control Factors   EDV   Filling time   Rate of venous return

Cardiodynamics   Cardiac Reserve   The difference between resting and maximal cardiac output

Cardiodynamics   The Heart and Cardiovascular System   Cardiovascular regulation   Ensures adequate circulation to body tissues

  Cardiovascular centers   Control heart and peripheral blood vessels

  Cardiovascular system responds to   Changing activity patterns   Circulatory emergencies

Cardiodynamics