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Questions and Answers

What occurs during repolarization of cardiomyocytes?

  • Na+ channels remain open
  • K+ ions exit cardiomyocytes (correct)
  • Ca channels open
  • K+ ions enter cardiomyocytes

    • What characterizes the absolute refractory period in cardiomyocytes?

  • This period is very short
  • Cells can respond to weak stimuli
  • Cells can respond to strong stimuli
  • Cells cannot respond at all (correct)

    • What is the typical duration range of a cardiac action potential?

  • 50–100 msec
  • 500–600 msec
  • 100–150 msec
  • 250–300 msec (correct)

    • During which phase of the cardiac cycle does atrial contraction occur?

    <p>Atrial systole (A)</p> Signup and view all the answers

    What does the QRS complex on an ECG represent?

    <p>Ventricular depolarization (D)</p> Signup and view all the answers

    Which of the following factors can lead to abnormal ECG changes?

    <p>Electrolyte disturbances (B)</p> Signup and view all the answers

    What is the primary purpose of the cardiac cycle?

    <p>To ensure proper heart contraction and blood flow (A)</p> Signup and view all the answers

    Which wave on an ECG indicates ventricular repolarization?

    <p>T wave (B)</p> Signup and view all the answers

    What is a primary function of the connective tissue fibers in the heart?

    <p>Support cardiac muscle fibers and prevent overexpansion (A)</p> Signup and view all the answers

    Which artery supplies blood to the right atrium and right ventricle?

    <p>Right coronary artery (D)</p> Signup and view all the answers

    What characterizes the left ventricle compared to the right ventricle?

    <p>Larger size and thicker walls (B)</p> Signup and view all the answers

    What is the primary cause of coronary artery disease (CAD)?

    <p>Atherosclerosis leading to blockage of coronary arteries (C)</p> Signup and view all the answers

    What is a characteristic of cardiac tissue's automaticity?

    <p>Can spontaneously contract without neural stimulation (A)</p> Signup and view all the answers

    What is the role of the sinoatrial (SA) node?

    <p>Initiates and regulates the heartbeat (A)</p> Signup and view all the answers

    Which cardiac veins empty into the coronary sinus?

    <p>Great cardiac vein, small cardiac veins, and middle cardiac veins (B)</p> Signup and view all the answers

    What occurs during a myocardial infarction?

    <p>Necrosis of part of the heart muscle (A)</p> Signup and view all the answers

    How do coronary anastomoses contribute to heart function?

    <p>They stabilize blood supply to cardiac muscle (D)</p> Signup and view all the answers

    What distinguishes conducting cells in the heart from contractile cells?

    <p>Conducting cells control and coordinate heartbeat, while contractile cells produce contractions (B)</p> Signup and view all the answers

    What is the innermost layer of the heart called?

    <p>Endocardium (C)</p> Signup and view all the answers

    Which type of epithelium composes the endocardium?

    <p>Simple squamous epithelium (B)</p> Signup and view all the answers

    What condition is characterized by the inflammation of the heart?

    <p>Carditis (C)</p> Signup and view all the answers

    Which of the following describes pericardial effusion?

    <p>Abnormal accumulation of fluid in the pericardial cavity (C)</p> Signup and view all the answers

    The coronary sulcus serves to divide which parts of the heart?

    <p>Atria and ventricles (B)</p> Signup and view all the answers

    What is the term for the incomplete closure of the heart's septum that can lead to congenital heart disease?

    <p>Interatrial septal defect (B)</p> Signup and view all the answers

    Which structure provides support to the valves of the heart?

    <p>Chordae tendineae (A)</p> Signup and view all the answers

    What does myocardial ischemia refer to?

    <p>Insufficient blood flow to the heart muscle (B)</p> Signup and view all the answers

    Which vessel carries oxygenated blood from the lungs to the left atrium?

    <p>Pulmonary veins (B)</p> Signup and view all the answers

    The ligamentum arteriosum is a remnant of which fetal structure?

    <p>Ductus arteriosus (C)</p> Signup and view all the answers

    Which of the following structures separates the left and right ventricles?

    <p>Anterior interventricular sulcus (A), Posterior interventricular sulcus (D)</p> Signup and view all the answers

    Which of the following is NOT a component of the heart's anatomy?

    <p>Septum primum (B)</p> Signup and view all the answers

    What component helps in sealing the valves during the ventricular contraction?

    <p>Papillary muscles (A)</p> Signup and view all the answers

    What occurs during atrial systole in the cardiac cycle?

    <p>Atrial contraction begins and AV valves remain open (A)</p> Signup and view all the answers

    At which point do the ventricles contain the maximum volume?

    <p>At the end of atrial systole (B)</p> Signup and view all the answers

    What happens during the isovolumetric contraction phase?

    <p>All the heart valves are closed and pressure rises in the ventricles (C)</p> Signup and view all the answers

    Which phase follows the isovolumetric contraction phase?

    <p>Rapid ejection phase (D)</p> Signup and view all the answers

    What is the main characteristic of the reduced ejection phase?

    <p>There is a slower rate of blood ejection from the ventricles (C)</p> Signup and view all the answers

    What occurs during the isovolumetric relaxation phase?

    <p>The ventricles are relaxed but blood volume remains constant (A)</p> Signup and view all the answers

    During which phase do the AV valves close?

    <p>Isovolumetric contraction (C)</p> Signup and view all the answers

    What is the pressure in the left ventricle during the rapid ejection phase?

    <p>It rapidly rises as blood is ejected (A)</p> Signup and view all the answers

    Which type of valve connects the right atrium to the right ventricle?

    <p>Tricuspid valve (A)</p> Signup and view all the answers

    What is the primary function of the chordae tendineae?

    <p>To attach valve cusps to papillary muscles (D)</p> Signup and view all the answers

    What happens during regurgitation in terms of blood flow?

    <p>Blood backflows into the opposite direction (D)</p> Signup and view all the answers

    Which valve is solely responsible for regulating blood flow between a ventricle and a great artery?

    <p>Aortic valve (B), Pulmonary valve (D)</p> Signup and view all the answers

    What distinguishes the mitral valve from other heart valves?

    <p>It connects the left atrium to the left ventricle. (C)</p> Signup and view all the answers

    Which structure is responsible for the prevention of backward flow into the atria during ventricular contraction?

    <p>Chordae tendineae (D)</p> Signup and view all the answers

    What is the result if the foramen ovale fails to close after birth?

    <p>Atrial Septal Defect (ASD) (A)</p> Signup and view all the answers

    Which of the following best describes the aortic valve?

    <p>It has three cusps and is located between the left ventricle and aorta. (D)</p> Signup and view all the answers

    What characteristic defines semilunar valves?

    <p>They do not have chordae tendineae. (B)</p> Signup and view all the answers

    What is a common cause of valve stenosis?

    <p>Valve calcification (D)</p> Signup and view all the answers

    What occurs to heart valves during ventricular contraction?

    <p>They open to allow blood flow to the great vessels. (A)</p> Signup and view all the answers

    Which of the following correctly describes the right ventricular pathway of blood circulation?

    <p>Right atrium to tricuspid valve to right ventricle. (C)</p> Signup and view all the answers

    In a healthy heart, how does the pressure in the ventricles affect the valves?

    <p>Increased pressure always closes the valves. (B)</p> Signup and view all the answers

    What is the primary function of the semilunar valves during ventricular ejection?

    <p>Allow blood to flow into the pulmonary trunk and aorta (C)</p> Signup and view all the answers

    Which physiological process does preload refer to?

    <p>The ventricular stretching during diastole (A)</p> Signup and view all the answers

    What is the ejection fraction if the stroke volume (SV) is 70 ml and the end-diastolic volume (EDV) is 120 ml?

    <p>60% (D)</p> Signup and view all the answers

    Which heart sound is associated with the closure of the semilunar valves?

    <p>S2 (D)</p> Signup and view all the answers

    How is cardiac output (CO) calculated?

    <p>HR × SV (D)</p> Signup and view all the answers

    Which of the following mechanisms increases heart rate due to increased central venous pressure?

    <p>Bainbridge Reflex (A)</p> Signup and view all the answers

    What is end-systolic volume (ESV) a measure of?

    <p>Blood volume in ventricles at the end of systole (A)</p> Signup and view all the answers

    What is the effect of sympathetic innervation on heart rate?

    <p>Increases heart rate (C)</p> Signup and view all the answers

    What is a heart murmur typically caused by?

    <p>Turbulence due to valve issues (C)</p> Signup and view all the answers

    What role do chemoreceptors play in regulating heart function?

    <p>Detect changes in arterial oxygen and carbon dioxide levels (C)</p> Signup and view all the answers

    What does the term 'cardiac reserve' refer to?

    <p>The ability to increase cardiac output from rest to maximum (D)</p> Signup and view all the answers

    In which phase of the cardiac cycle do all heart valves remain closed?

    <p>Isovolumetric relaxation (B)</p> Signup and view all the answers

    Which factor does NOT affect stroke volume?

    <p>Heart Rate (A)</p> Signup and view all the answers

    Study Notes

    Fluid & Transport Part 2

    • The cardiovascular system is organized into a heart, blood vessels, and blood.
    • The heart acts as a pump for blood.
    • Blood vessels are the conducting system that transports blood.
    • Blood is the fluid medium that is pumped and transported.

    Organization of the Cardiovascular System

    • The heart has four chambers: two atria and two ventricles.
    • The atria are thin-walled and receive blood.
    • The ventricles are thick-walled and pump blood.
    • The heart is divided into right and left sides by the interatrial and interventricular septum.
    • The right side of the heart pumps blood to the lungs.
    • The left side of the heart pumps blood to the body.
    • The pulmonary circuit carries blood to and from the lungs.
    • The systemic circuit carries blood to and from the body.
    • Capillaries are the tiny blood vessels that connect arteries and veins, enabling gas and nutrient exchange.

    The Heart

    • The heart is a muscular organ located within the mediastinum of the thoracic cavity.
    • It's located slightly to the left of the sternum and posterior to the sternum.
    • It's situated between the lungs.
    • It's surrounded by the pericardial sac, a fibrous tissue layer that stabilizes the heart.
    • The base of the heart connects to the great vessels.
    • The apex of the heart is located in the 5th left intercostal space, just inside the midclavicular line.

    Heart Chambers

    • The heart has four chambers: two atria and two ventricles.
    • The right and left atria are thin-walled, while the right and left ventricles are thick-walled.
    • The right and left atria are separated by the interatrial septum.
    • The right and left ventricles are separated by the interventricular septum.
    • Valves in the heart help direct the one-way flow of blood.

    Blood Circulation

    • The systemic circulation moves blood to and from the body.
    • The pulmonary circulation moves blood to and from the lungs.
    • Blood continuously circulates between these two circuits.
    • One full cycle involves the movement from the body to the heart, to the lungs, and back to the body.

    Heart Chambers & Circulation

    • The right atrium receives blood from the systemic circuit.
    • The right ventricle pumps blood to the pulmonary circuit.
    • The left atrium receives blood from the pulmonary circuit.
    • The left ventricle pumps blood to the systemic circuit.

    Blood Vessels

    • Arteries carry blood away from the heart to tissues and organs in the body.
    • Veins carry blood back to the heart from the tissues.
    • Capillaries form a network between arteries and veins for nutrient and waste exchange.

    Location of the Heart

    • The heart is located in the mediastinum within the thoracic cavity.
    • It's directly behind the sternum, slightly to the left, and between the lungs.

    Mediastinum

    • The mediastinum is the central part of the thoracic cavity.
    • It's bordered by the thoracic vertebrae, sternum, and the lungs or pleurae.
    • The heart and other thoracic organs lie within it, excluding the lungs.

    Location of the Heart (Pericardial Sac)

    • The heart lies within the pericardial sac.
    • The pericardial sac is a fibrous tissue layer that both surrounds and stabilizes the heart.

    Surface Anatomy of the Heart

    • The heart's base is its superior end connected to the great vessels.
    • The pointed apex is located in the 5th left intercostal space, inside the midclavicular line.

    Layers of the Heart Wall

    • The heart wall has three layers: pericardium, myocardium, and endocardium.
    • The outer layer is the pericardium, which consists of parietal pericardium and visceral pericardium.
    • The middle layer, myocardium, is the muscular layer.
    • The innermost layer is the endocardium.

    Pericardium

    • The pericardium is a two-layered membrane.
    • The outer layer is the parietal pericardium, which is attached to the pericardial sac.
    • The inner layer is the visceral pericardium (epicardium), attached to the heart.
    • The pericardial cavity is between the layers, containing pericardial fluid for lubrication.

    Myocardium

    • The myocardium is the thickest layer of the heart.
    • It's made of concentric layers of cardiac muscle tissue, with atrial and ventricular myocardium.
    • Cardiomyocytes make up the myocardium.

    Characteristics of Cardiomyocytes

    • Cardiomyocytes are small, involuntary, mononucleated and striated.
    • They have branching interconnected structures (intercalated discs or gap junctions), short wide T tubules and no terminal cisternae (SR).
    • These cells use aerobic respiration and have high concentrations of mitochondria and myoglobin, enabling sustained contraction.
    • Intercalated discs enable mechanical, chemical, and electrical coupling between cells, producing a coordinated heartbeat.

    Intercalated Discs

    • Intercalated discs are specialized contact points where adjacent cardiomyocytes connect.
    • These structures provide mechanical, chemical, and electrical coupling, allowing heart cells to contract as a unit.

    Cardiac vs. Skeletal Muscle Cells

    • Cardiac muscle cells are smaller, have one nucleus (often), and have shorter T tubules compared to skeletal muscle fibers (which have multiple).
    • Cardiac muscle cells have a more extensive blood supply than skeletal muscle cells.
    • Skeletal muscle fibers require the activity of motor neurons to function, while cardiac muscle fibers are automatically stimulated through the action of pacemaker cells.

    Endocardium

    • The endocardium lines the inner surface of the heart, including the heart valves.
    • It's made of simple squamous epithelium and is continuous with the endothelium of the great vessels.

    Diseases of the Cardiac Wall

    • Carditis (inflammation of the heart) includes pericarditis, myocarditis, and endocarditis.
    • Pericardial effusion is abnormal fluid accumulation in the pericardial cavity.
    • Myocardial ischemia is inadequate blood flow to the heart muscle.

    Superficial Surface of the Heart

    • The coronary sulcus divides the atria from the ventricles.
    • The anterior and posterior interventricular sulci separate the left and right ventricles.
    • The superficial heart contains blood vessels supplying the cardiac muscle.

    Internal Anatomy of the Heart

    • The internal anatomy shows internal structures, the valves and vessels, and muscular components and chambers.

    Heart Valves

    • One-way valves allow blood flow in one direction, preventing backflow.
    • Valves consist of fibrous flaps (cusps).
    • The mitral and tricuspid valves are atrioventricular valves.
    • Chordae tendineae attach to the papillary muscles to prevent valve inversion.

    Valve Groups

    • Two atrioventricular (AV) valves (tricuspid and mitral) connect atria and ventricles.
    • Two semilunar valves (pulmonary and aortic) connect the ventricles to great arteries.

    Atrioventricular (AV) Valves

    • These valves allow blood to flow from the atria to the ventricles.
    • The tricuspid valve is between the right atrium and ventricle.
    • The mitral (bicuspid) valve is between the left atrium and ventricle.

    Semilunar Valves

    • Semilunar valves allow blood to flow from the ventricles to the major arteries.
    • The pulmonary valve is between the right ventricle and the pulmonary artery.
    • The aortic valve is between the left ventricle and the aorta.

    Valve Lesions

    • Regurgitation (incompetence) occurs due to valves failing to close properly, resulting in backflow.
    • Stenosis is reduced blood flow due to valve narrowing.
    • Valve problems can be congenital (inborn) or caused by factors like rheumatic fever.

    Pathway of Blood Circulation

    • Deoxygenated blood from the body enters the right atrium through the superior and inferior vena cava.
    • Then moves to the right ventricle, through the pulmonary circuit and lungs for re-oxygenation.
    • Oxygenated blood returns to the left atrium via pulmonary veins.
    • From the left atrium to the left ventricle, then through the systemic circuit to the rest of the body.

    Foramen Ovale

    • The foramen ovale is an opening in the interatrial septum that connects the two atria.
    • It seals off after birth, but failure will lead to condition known as Atrial Septal Defect (ASD).

    Right vs Left Ventricle

    • The left ventricle is larger and thicker.
    • The right ventricle is smaller and thinner.
    • Both ventricles, however, hold the same blood volume.

    Connective Tissue Fibers of the Heart

    • Connective tissue fibers structurally support cardiac muscle fibers.
    • They distribute contraction forces to prevent overexpansion of the heart.
    • Elastic fibers enable the heart to return to its original shape after contractions.

    Blood Supply to the Heart (Coronary Circulation)

    • Coronary arteries supply blood to the cardiac muscle tissue.
    • Coronary veins drain the blood away, returning it to the heart.

    Coronary Arteries

    • Right and left coronary arteries originate at the aortic sinuses.
    • High blood pressure and elastic recoil help propel blood through the coronary arteries during diastole.

    Right Coronary Artery

    • Supplies blood to the right atrium, sinoatrial node, atrioventricular node, part of the left ventricle and branches include: marginal and posterior descending artery/branch.

    Left Coronary Artery

    • Supplies blood to the left atrium, left ventricle, and the interventricular septum.
    • Branches include circumflex and anterior descending artery/branch.

    Coronary Anastomoses

    • Coronary anastomoses are connections between coronary arteries and branches.
    • They help stabilize blood supply to the cardiac muscle in cases of blockage.

    Coronary (Cardiac) Veins

    • Anterior cardiac veins, posterior, middle, and small cardiac veins drain blood from the anterior and posterior surfaces of the heart.
    • Great cardiac vein drains blood in the anterior region.
    • Coronary sinus is a major vein that receives blood from the cardiac veins, before returning the blood into the right atrium.

    Coronary Artery Disease (CAD)

    • CAD involves the narrowing or blockage of coronary arteries.
    • This reduces the flow which can lead to reduced oxygen delivery (ischemia) to heart tissue.
    • The most common cause of CAD is atherosclerosis, a condition where fatty deposits build up in artery walls, reducing blood flow.

    Coronary Artery Disease (CAD) Manifestations

    • CAD can be asymptomatic.
    • Symptoms include angina pectoris (chest pain), myocardial infarction (heart attack), and sudden death.

    Physiological Characteristics of Cardiac Tissue

    • Automaticity is the ability of heart tissue to contract without neural stimulation.
    • Contractibility is the degree to which heart muscle can contract.
    • Conductivity refers to the ability of cardiac tissue to conduct an electrical impulse throughout the heart.
    • Excitability is the ability to respond to electrical stimulation.

    Heartbeat

    • A heartbeat is a single contraction of the whole heart.
    • The atria contract first, then the ventricles in a coordinated sequence.

    Types of Cardiac Muscle Cells

    • Contractile cells are the main functional cells, contracting to produce the blood pumping action.
    • Conducting cells are specialized cells that initiate and transmit the electrical impulses responsible for coordinating the heartbeat.

    Conducting System

    • The heart's conducting system is a network of specialized cardiac muscle cells.
    • It initiates and transmits electrical impulses, coordinating the contraction of the heart.
    • The system enables a synchronized rhythmic contraction of the heart chambers.

    Structures of the Conducting System

    • The sinoatrial node (SA node) initiates the heartbeat.
    • Internodal pathways carry the impulse across the atria.
    • The atrioventricular node (AV node) delays the impulse to allow the atria to empty into the ventricles before ventricular contraction.
    • The AV bundle (bundle of His) transmits the impulse into the ventricles.
    • The bundle branches route the impulse throughout the ventricles.
    • Purkinje fibers rapidly spread the impulse to the ventricular myocardium, leading to ventricular contraction.

    Impulse Conduction Through the Heart

    • The electrical impulse travels from the SA node, through the internodal pathways, to the AV node, then through the AV bundle and bundle branches to the Purkinje fibers.
    • The impulse spreads throughout the ventricles, coordinating their contraction.

    Sinoatrial (SA) Node

    • The SA node is the heart's natural pacemaker.
    • It initiates the electrical impulses, setting the heart rate.
    • The SA node creates 80-100 automatic action potentials per minute.

    Heart Rate (HR)

    • Heart rate is the number of heartbeats per minute.
    • Normal heart rate is 60-90 beats/minute.
    • The heart rate is regulated by the ANS and hormones.

    Abnormal Pacemaker Function

    • Bradycardia is abnormally slow heart rate below 60 bpm.
    • Tachycardia is abnormally fast heart rate above 90 bpm.
    • Ectopic pacemakers, abnormal cells, create fast unusual rhythms.
    • Sick sinus syndrome affects the SA node, altering rhythm.

    Action Potential in The Cardiac Muscle

    • Cardiac action potentials have a plateau phase, distinguishing them from skeletal muscle action potentials.
    • This plateau is due to calcium ion entry, prolonging the refractory period, and preventing tetanus (sustained contractions).

    Resting Potential

    • Ventricular cells have a resting membrane potential of about -90 mV.
    • Atrial cells have a resting membrane potential of about -80 mV.

    Steps of Cardiac Action Potential

    • Rapid depolarization (opening of fast Na+ channels).
    • Plateau phase (Ca2+ entry).
    • Repolarization (opening of slow K+ channels).

    Repolarization

    • It involves the closing of Ca2+ channels and the opening of potassium (K+) channels
    • The outflow of potassium ions returns the resting potential of the cardiac muscle cell, leading to its depolarization.

    Refractory Periods

    • Absolute refractory period is a time period wherein cardiac muscle cells cannot respond to further stimulation, preventing summation and tetanus.
    • The refractory period is longer than the typical refractory period for skeletal muscle.

    Duration of Cardiac Action Potential

    • Cardiac action potentials last significantly longer than skeletal muscle action potentials (250-300 msec).
    • The prolonged refractory period is crucial to prevent tetanus and ensure synchronized myocardial contractions.

    Ca2+ & Myocardial Contraction

    • Contraction in a cardiac muscle cell requires an increase in calcium (Ca2+) concentration around myofibrils.
    • Cardiac muscle tissues are sensitive to changes in calcium concentrations.

    Electrocardiogram (ECG - EKG)

    • ECG is a recording of electrical events in the heart.
    • Electrodes placed on the body measure the electrical activity of the heart.
    • An ECG can indicate abnormal electrical activity in the heart.

    Features of ECG

    • The P wave indicates atrial depolarization (atrial contraction).
    • The QRS complex denotes ventricular depolarization (ventricular contraction).
    • The T wave indicates ventricular repolarization (ventricular relaxation).
    • P-R interval: period from beginning of atrial depolarization to the start of ventricular depolarization.
    • Q-T interval: time from the start of ventricular depolarization to the end of ventricular repolarization.

    ECG Waves Timing

    • Timing differs for various ECG waves and intervals due to various anatomical and physiological factors.

    Normal ECG Tracing

    • Shows waveforms indicating the normal rhythm and sequence of heart activity.

    Abnormal ECG

    • Abnormal ECGs show various potential heart disease, hypertrophy, and changes in electrolyte balance.

    Cardiac Dysrhythmias

    • Dysrhythmias (arrhythmias or irregular rhythms) in the heart indicate abnormal electrical activity, not always a sign of substantial health problems.
    • Different ECG waveforms and patterns signal various kinds of abnormalities.

    Cardiac Cycle

    • Cardiac cycle is the period from the start of one heart beat to the beginning of the next.
    • Atrial systole—contraction of atria.
    • Atrial diastole—relaxation of atria.
    • Ventricular systole- contraction of ventricles.
    • Ventricular diastole—relaxation of ventricles.

    Cardiac Cycle & Pressure

    • Blood pressure changes during each phase of the cardiac cycle.
    • Blood flows from high pressure to low pressure areas.
    • Valve movements help direct blood unidirectionally.

    Cardiac Cycle & Heart Rate

    • The heart rate influences the duration of the cardiac cycle.
    • Faster heart rates result in shorter cardiac cycles.

    4 Main Events of Cardiac Cycle

    • Cardiac cycle includes atrial systole, atrial diastole, ventricular systole, and ventricular diastole.
    • These phases occur in a specific order during each heartbeat.

    Phases of The Cardiac Cycle

    • Cardiac cycle includes atrial contraction phase in that order, isovolumetric contraction, rapid ejection, reduced ejection, isovolumetric relaxation, rapid filling, and reduced filling phase.

    Phases of The Cardiac Cycle

    • Atrial systole initiates with atrial contraction, during which time ventricles are filling.
    • During atrial systole, atria eject blood into ventricles. Atrial systole is then terminated with closing of AV valves.
    • In ventricular systole, isovolumetric contraction occurs, during which time pressure rises but blood is not expelled.
    • Ventricular ejection occurs following the closing of AV valves, with subsequent opening of semilunar valves. During ventricular ejection, blood goes into pulmonary trunk and aorta.
    • Ventricular pressure falls in the later part of ventricular systole causing semilunar valves to close, terminating ventricular systole.
    • Ventricular diastole occurs as ventricles relax. AV valves begin to open allowing blood into ventricles.

    Phases of Cardiac Cycle

    • Ventricular diastole (isovolumetric relaxation) begins with ventricular pressure dropping below atrial pressure, allowing AV valves to open, resulting in passive ventricular filling. In this phase, atrial pressure becomes higher than ventricular pressure leading to passive atrial emptying.

    Heart Sounds

    • Heart sounds are produced by the vibrations during valve closure, as blood flows into different heart chambers.
    • Loud sounds, such as S1, are due to the closing of AV valves, whereas soft sounds, like S4, are due to atrial contraction.

    Heart Murmurs

    • Heart murmurs are turbulent blood flows through the heart, due to problems with valves or heart structure.

    Energy of Heart

    • The heart primarily utilizes aerobic respiration, which means it uses oxygen to break down fats and glucose (main source of energy) for ATP generation.
    • Cardiac muscle stores oxygen in myoglobin, which supports its continuous functional demands.

    Autonomic Innervation of the Heart

    • The heart receives autonomic innervation through the sympathetic and parasympathetic nervous systems.
    • Parasympathetic fibers travel through the vagus nerve, affecting the heart via cardiac plexuses, delivering primarily impulses that decrease heart rate (slow impulses).
    • Sympathetic fibers deliver impulses from cervical and upper thoracic ganglia delivering impulses that increase heart rate.

    Autonomic Innervation of the Heart

    • Sympathetic and parasympathetic systems innervate the heart via cardiac plexuses.
    • Cardiac centers in the medulla oblongata, controlled by pathways, regulate these autonomic activities, adjusting heart rate to maintain dynamic balance.
    • Monitor cardiac reflexes such as baroreceptors and chemoreceptors.

    Autonomic Innervations of the Heart

    • Sympathetic innervation affects both atria and ventricles, affecting the heart rate (increasing).
    • Parasympathetic innervation only affects the atria, primarily decreasing heart rate.
    • Dual innervation implies having both sympathetic and parasympathetic fibers (tone), which enables fine adjustments to the heart rate in response to different body needs.

    Cardiodynamics

    • Cardiodynamics is the study of the heart's mechanical function and includes blood volume in ventricles at heart's diastole (EDV) and at heart's systole(ESV).
    • Ejection fraction involves percentage of blood ejected from a ventricle each beat.
    • Stroke volume is the blood volume ejected from a ventricle during each heartbeat.

    Preload & Afterload

    • Preload relates to ventricular stretching during diastole, resulting from venous return.
    • Afterload is the force the heart must overcome to eject blood, determined by the resistance encountered in the arteries.

    Cardiac Output (CO)

    • Cardiac output is the amount of blood pumped by each ventricle in one minute.
    • Calculated as CO = Heart rate (HR) x Stroke volume (SV).
    • Average cardiac output in humans is between 4900 and 5000 mL.

    Control of Cardiac Output

    • Heart rate is adjusted through the autonomic nervous system (ANS) and hormones (e.g., epinephrine, norepinephrine, thyroid hormones).
    • Stroke volume is affected by preload (venous return, filling time), contractility, and afterload (peripheral resistance).

    Factors affecting heart rate (HR) & stroke volume(SV)

    • Factors impacting heart rate include autonomic innervation (sympathetic and parasympathetic), hormones (e.g., epinephrine, thyroid hormones), and venous return (VR). -Factors concerning stroke volume include preload (determined by venous return and filling time), contractility (determined by sympathetic activity, hormones, etc), and afterload (artery resistance).

    Factors Control Heart Rate

    • Autonomic nervous system controls sympathetic and parasympathetic impulses via cardiac plexuses.
    • Circulating hormones (e.g., epinephrine, thyroid hormones) modulate HR.
    • Venous return (volume of blood returning to the heart) also impact heart rate.

    Factors Control Stroke Volume

    • Factors influencing stroke volume (SV) encompass factors affecting end-diastolic volume (EDV), such as filling time and venous return (preload).
    • Factors affecting end-systolic volume (ESV), such as contractility and afterload, are also considered.

    Bainbridge (Atrial) Reflex

    • Mechanistically, the Bainbridge reflex increases heart rate in response to increased venous return.
    • This reflex is triggered by stretch receptors in the right atrium, which respond to increased venous pressure, resulting in increased sympathetic activity.

    Starling Law

    • Starling's Law states that within physiological limits, the force of a cardiac muscle contraction is proportional to its initial length.
    • This principle emphasizes that greater preload results in greater stroke volume.

    Cardiac Reserve

    • Cardiac reserve is the difference between resting and maximum cardiac output.
    • Most healthy people can increase their cardiac output by 300-500%.

    Heart Failure

    • Heart failure occurs when the heart cannot pump blood sufficiently to meet the body's needs.
    • This can be due to various factors, leading to reduced blood flow to peripheral tissues and organs.

    Summary

    • The heart is a muscular pump with four chambers (2 atria, 2 ventricles) consisting of three layers per chamber(endocardium, myocardium, pericardium) with valves controlling blood flow.
    • The heart has two circuits: pulmonary and systemic.
    • The heart has a specialized conducting system (SA and AV nodes, bundles and branches, Purkinje fibers).
    • The cardiac cycle describes the sequence of events and phases during each heartbeat.
    • Cardiodynamics and factors affecting preload, afterload, and stroke volume relate to cardiac function, while heart failure represents the inability to effectively pump blood, lowering adequate organ perfusion.

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