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Chapter Notes for Lecture: E.N. Marieb, HUMAN ANATOMY & PHYSIOLOGY,5TH Edition, , Benjamine Cummings Publisher, 2001

Prepare from : V.A. Austin’s PowerPpoint Presentation (ISBN: 0-8053-5469-7), CD ROM: Pearson Education, Inc. , 2003.ter 19

 

The Cardiovascular System: The Heart

 

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 sternum

Heart Covering

•      Pericardial physiology

•    Protects and anchors heart

•    Prevents overfilling

Heart Covering

•      Pericardial anatomy

•    Fibrous pericardium

•    Serous pericardium (separated by pericardial cavity)

•    Epicardium (visceral layer)

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: Major Vessels of the Heart (Anterior View)

•      Returning blood to the heart

•    Superior and inferior venae cavae

•    Right and left pulmonary veins

•      Conveying blood away from the heart

•    Pulmonary trunk, which splits into right and left pulmonary arteries

•    Ascending aorta (three branches) – brachiocephalic, left common carotid, and subclavian arteries

External Heart: Vessels that Supply/Drain the Heart (Anterior View)

•      Arteries – right and left coronary (in atrioventricular groove), marginal, circumflex, and anterior interventricular

•      Veins – small cardiac vein, anterior cardiac vein, and great cardiac vein

External Heart: Major Vessels of the Heart (Posterior View)

•      Returning blood to the heart

•    Right and left pulmonary veins

•    Superior and inferior venae cavae

•      Conveying blood away from the heart

•    Aorta

•    Right and left pulmonary arteries

External Heart: Vessels that Supply/Drain the Heart (Posterior View)

•      Arteries – right coronary artery (in atrioventricular groove) and the posterior interventricular artery (in interventricular groove)

•      Veins – great cardiac vein, posterior vein to left ventricle, coronary sinus, and middle cardiac vein

Gross Anatomy of Heart: Frontal Section

•      Frontal section showing interior chambers and valves

•      Major vessels leading to and from the heart

Gross Anatomy of Heart: Frontal Section

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

Pathway of Blood through the Heart and Lungs

•      Right atrium ΰ tricuspid valve ΰ right ventricle

•      Right ventricle ΰ pulmonary semilunar valve ΰ pulmonary arteries ΰ lungs

•      Lungs ΰ pulmonary veins ΰ left atrium

•      Left atrium ΰ bicuspid valve ΰ left ventricle

•      Left ventricle ΰ aortic semilunar valve ΰ aorta

•      Aorta ΰ systemic circulation

Coronary Circulation

•      Coronary circulation is the functional blood supply to the heart

•      Collateral routes insure blood delivery to heart even if major vessels are occluded

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 muscles

•      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 ventricles

Microscopic Heart Muscle Anatomy

•      Cardiac muscle is striated, short, fat, branched, and interconnected

•      Connective tissue endomysium acts as both tendon and insertion

•      Intercalated discs anchor cardiac cells together and allow free passage of ions

•      Heart muscle behaves as a functional syncytium

Cardiac Muscle Contraction

•      Heart muscle:

•    Is stimulated by nerves and self-excitable (automaticity)

•    Contracts as a unit

•    Has a long (250 ms) absolute refractory period

•      Cardiac muscle contraction is similar to skeletal muscle contraction

Heart Physiology: Intrinsic Conduction System

•      Autorhythmic cells:

•    Initiate action potentials

•    Have unstable resting potentials called pacemaker potentials

•    Use calcium influx (rather than sodium) for rising phase of the action potential

Heart Physiology: Intrinsic Conduction System

Heart Physiology: Sequence of Excitation

•      Sinoatrial (SA) node generates impulses about 75 times/minute

•      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

Extrinsic Innervation of the Heart

•      Heart is stimulated by the sympathetic cardioacceleratory center

•      Heart is inhibited by the parasympathetic cardioinhibitory center

Electrocardiography

•      Electrical activity is recorded by electrocardiogram (ECG)

•      P wave corresponds to depolarization of SA node

•      QRS complex corresponds to ventricular depolarization

•      T wave corresponds to ventricular repolarization

•      Atrial repolarization record is masked by the larger QRS complex

Electrocardiography

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

•      Ventricular filling – mid-to-late diastole

•    Heart blood pressure is low as blood enters atria and flows into ventricles

•    AV valves are open then atrial systole occurs

•      Ventricular systole

•    Atria relax

•    Rising ventricular pressure results in closing of AV valves

•    Isovolumetric contraction phase

•    Ventricular ejection phase opens semilunar valves

Phases of the Cardiac Cycle

•      Isovolumetric relaxation – early diastole

•    Ventricles relax

•    Backflow of blood in aorta and pulmonary trunk closes semilunar valves

•      Dicrotic notch – brief rise in aortic pressure caused by backflow of blood rebounding off semilunar valves

Heart Sounds

•      Heart sounds (lub-dup) are associated with closing of heart valves

Cardiac Output (CO) and Reserve

•      CO is the amount of blood pumped by each ventricle in one minute

•      CO is the product of heart rate (HR) and stroke volume (SV)

•      HR is the number of heart beats per minute

•      SV is the amount of blood pumped out by a ventricle with each beat

•      Cardiac reserve is the difference between resting and maximal CO

Cardiac Output: Example

•      CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)

•      CO = 5250 ml/min (5.25 L/min)

Regulation of Stroke Volume

•      SV = end diastolic volume (EDV) minus end systolic volume (ESV)

•      EDV = amount of blood collected in a ventricle during diastole

•      ESV = amount of blood remaining in a ventricle after contraction     

Factors Affecting Stroke Volume

•      Preload – amount ventricles are stretched by contained blood

•      Contractility – cardiac cell contractile force due to factors other than EDV

•      Afterload – back pressure exerted by blood in the large arteries leaving the heart

Frank-Starling Law of the Heart

•      Preload, or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volume

•      Slow heartbeat and exercise increase venous return to the heart, increasing SV

•      Blood loss and extremely rapid heartbeat decrease SV

Preload and Afterload

Extrinsic Factors Influencing Stroke Volume

•      Contractility is the increase in contractile strength, independent of stretch and EDV

•      Increase in contractility comes from:

•    Increased sympathetic stimuli

•    Certain hormones

•    Ca2+ and some drugs

•      Agents/factors that decrease contractility include:

•    Acidosis

•    Increased extracellular potassium

•    Calcium channel blockers

Contractility and Norepinephrine

•      Sympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger system

Regulation of Heart Rate: Autonomic Nervous System

•      Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise

•      Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS

•      PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone

Bainbridge Reflex

•      Bainbridge (atrial) reflex – a sympathetic reflex initiated by increased blood in the atria

•    Causes stimulation of the SA node

•    Stimulates baroreceptors in the atria, causing increased SNS stimulation

Chemical Regulation of the Heart

•      The hormones epinephrine and thyroxine increase heart rate

•      Intra- and extracellular ion concentrations must be maintained for normal heart function

Factors Involved in Regulation of Cardiac Output

Homeostatic Imbalances

•      Hypocalcemia – reduced ionic calcium depresses the heart

•      Hypercalcemia – dramatically increases heart irritability and leads to spastic contractions

•      Hypernatremia – blocks heart contraction by inhibiting ionic calcium transport

•      Hyperkalemia – leads to heart block and cardiac arrest

Homeostatic Imbalances

•      Tachycardia – heart rate over 100 beats/min

•      Bradycardia – heart rate less than 60 beats/min

Congestive Heart Failure (CHF)

•      Congestive heart failure (CHF), caused by:

•    Coronary atherosclerosis

•    Increased blood pressure in aorta

•    Successive myocardial infarcts

•    Dilated cardiomyopathy (DCM)

Developmental Aspects of the Heart

•      Embryonic heart chambers

•    Sinus venous

•    Atrium

•    Ventricle

•    Bulbus cordis

Developmental Aspects of the Heart

•      Fetal heart structures that bypass pulmonary circulation

•    Foramen ovale connects the two atria

•    Ductus arteriosus connects pulmonary trunk and the aorta

Age-Related Changes Affecting the Heart

•      Sclerosis and thickening of valve flaps

•      Decline in cardiac reserve

•      Fibrosis of cardiac muscle

•      Atherosclerosis