Cardiovascular System
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Questions and Answers

What are the two general mechanisms that cause the plateau in the action potential in cardiac muscle?

  • Increased permeability for potassium ions
  • Additional activation of L-type calcium channels (slow calcium channels) (correct)
  • Rapid increase in opening of fast sodium channels (correct)
  • Decreased permeability for potassium ions

    • Explain how slow calcium channels cause the action potential in cardiac muscle to be different than that of skeletal muscle.

    Slow calcium channels in cardiac muscle prolong the depolarization phase, leading to a longer action potential duration compared to skeletal muscle. This extended depolarization allows for a more sustained contraction needed for efficient blood pumping.

    Compare the relative velocity of signal conduction in cardiac muscle fibers to Purkinje fibers.

    Purkinje fiber conduction is much faster than cardiac muscle fiber conduction, ensuring rapid electrical signal transmission throughout the heart.

    The absolute refractory period in cardiac muscle is when the heart cannot be stimulated to contract at all.

    <p>True</p> Signup and view all the answers

    The relative refractory period is when the heart can be stimulated to contract by a strong signal.

    <p>True</p> Signup and view all the answers

    Why is the extracellular calcium concentration of greater relevance for cardiac muscle contraction compared to skeletal muscle contraction?

    <p>Cardiac muscle relies heavily on extracellular calcium for contraction, whereas skeletal muscle relies on intracellular calcium stores. This difference is due to the unique structure of cardiac muscle, where the t-tubules connect to the extracellular fluid, facilitating calcium influx.</p> Signup and view all the answers

    What is the relationship between heart rate, the duration of the action potential, duration of the cardiac cycle, and the relative durations of systole and diastole?

    <p>As heart rate increases, the duration of the action potential plateau and time in systole decreases. Consequently, the time in diastole also decreases, leading to a higher ratio of systole to diastole.</p> Signup and view all the answers

    Explain how ventricular volume, atrial pressure, aortic pressure, and left ventricular pressure change over the course of the cardiac cycle, and relate this to the electrocardiogram (ECG) and phonocardiogram.

    <p>During the cardiac cycle, ventricular volume increases during filling, reaches a peak during isovolumetric contraction, and then decreases during ejection. Atrial pressure rises before ventricular contraction to assist in filling, while aortic pressure increases sharply during ejection. Left ventricular pressure follows a similar pattern to aortic pressure, reflecting the ejection of blood into the aorta.</p> Signup and view all the answers

    Describe the role of atrial contraction in the cardiac cycle, including its relative contribution to ventricular filling.

    <p>Atrial contraction plays a minor but significant role in ventricular filling, contributing about 20% of the total volume. This pre-ventricular contraction helps to ensure a more complete ventricular filling, which is especially important during periods of increased heart rate or when ventricular filling is compromised.</p> Signup and view all the answers

    What is the "period of rapid filling of the ventricles" and what mechanisms contribute to it?

    <p>The period of rapid filling occurs at the onset of ventricular diastole, when the AV valves open due to the pressure difference between relaxed ventricles and the atria, allowing blood to flow passively into the ventricles.</p> Signup and view all the answers

    Why does isovolumetric contraction occur before ventricular ejection?

    <p>Isovolumetric contraction occurs before ejection because the ventricles must build up sufficient pressure to overcome the pressure in the aorta or pulmonary artery, allowing for the opening of the semilunar valves and the start of blood ejection.</p> Signup and view all the answers

    Differentiate between the "period of rapid ejection" and the "period of slow ejection" during ventricular systole.

    <p>During rapid ejection, the ventricles expel a larger volume of blood due to the higher pressure gradient between the ventricle and the aorta. As the pressure gradient declines, the rate of ejection slows down, resulting in a period of slow ejection. This difference in ejection rate is a natural consequence of the changing pressure dynamics within the heart.</p> Signup and view all the answers

    Explain what the ejection fraction is, including how it is calculated, and state the normal value for ejection fraction at rest in healthy individuals.

    <p>Ejection fraction (EF) is the proportion of blood ejected from the ventricle during each beat. It is calculated as (EDV - ESV) / EDV, where EDV is end-diastolic volume (volume of blood in ventricle at the end of filling) and ESV is end-systolic volume (volume of blood remaining in ventricle after ejection). The normal ejection fraction at rest is about 60%.</p> Signup and view all the answers

    Compare the pressures between the right and left ventricles during systole.

    <p>The pressures in the right ventricle are significantly lower than the pressures in the left ventricle during systole. This difference is due to the lower pressure needed to pump blood through the pulmonary circulation compared to the systemic circulation.</p> Signup and view all the answers

    Preload refers to the degree of tension in the heart muscle when it begins to contract.

    <p>True</p> Signup and view all the answers

    Afterload is the resistance the heart must overcome to eject blood into the aorta.

    <p>True</p> Signup and view all the answers

    Briefly describe the two key factors underlying the Frank-Starling mechanism.

    <p>The Frank-Starling mechanism highlights two key factors: increased preload enhances contractile force and thus stroke volume, and increased stretch of the heart muscle fibers increases elastic energy leading to greater contractile strength.</p> Signup and view all the answers

    Trace the pathway of electrical conduction from the SA node through the epicardial surface of the heart.

    <p>The electrical conduction pathway begins at the SA node, spreads through the internodal pathways, reaches the AV node, then travels through the AV bundle, bundle branches, and finally reaches the Purkinje fibers in the ventricular muscle.</p> Signup and view all the answers

    Compare the intrinsic rhythmical rates of the SA node, AV node, and Purkinje fibers. Explain the concept of ectopic beats and escape beats.

    <p>The SA node has the fastest intrinsic rate (70-80 beats per minute), followed by the AV node (40-60 beats per minute), and lastly the Purkinje fibers (15-40 beats per minute). Ectopic beats originate from locations other than the SA node, while escape beats occur when the ventricle takes over pacing due to a failure of the SA or AV node to initiate impulses.</p> Signup and view all the answers

    Intrinsic heart rate represents the heart rate when the heart is not influenced by the autonomic nervous system.

    <p>True</p> Signup and view all the answers

    The sympathetic nervous system slows down the heart rate while the parasympathetic nervous system speeds it up.

    <p>False</p> Signup and view all the answers

    What are the neurotransmitters released by the sympathetic and parasympathetic nerves to the heart?

    <p>The sympathetic nervous system releases norepinephrine (NE), while the parasympathetic nervous system releases acetylcholine (ACh).</p> Signup and view all the answers

    Identify why the sympathetic nervous system is able to increase contractile force of cardiac muscle.

    <p>The sympathetic nervous system stimulates beta-adrenergic receptors on cardiac muscle cells, leading to increased intracellular calcium levels. This elevated calcium concentration enhances the strength of muscle contractions, resulting in a more powerful heartbeat.</p> Signup and view all the answers

    Tachycardia is a faster than normal heart rate at rest, while bradycardia is a slower than normal heart rate at rest.

    <p>True</p> Signup and view all the answers

    Tachycardia during exercise is not considered abnormal.

    <p>True</p> Signup and view all the answers

    What is the difference between skeletal muscle and cardiac muscle?

    <p>Skeletal muscle is voluntary, striated, and contains many nuclei per cell. Cardiac muscle is involuntary, striated, and typically has one nucleus per cell. They both contain actin and myosin, but cardiac muscle has intercalated discs that help with communication and rapid diffusion of ions.</p> Signup and view all the answers

    What are the two main mechanisms that cause the plateau in the action potential in cardiac muscle?

    <p>Decreased permeability to potassium ions and activation of L-type calcium channels</p> Signup and view all the answers

    What is the role of papillary muscles and chordae tendinae in the heart?

    <p>Papillary muscles are connected to AV valves through chordae tendinae. They help to prevent the valve from prolapsing back into the atria during ventricular contraction, ensuring proper blood flow from the atria to the ventricles.</p> Signup and view all the answers

    Semilunar valves are designed to handle faster blood velocity compared to AV valves?

    <p>True</p> Signup and view all the answers

    Which of the following is NOT a factor that influences the stroke volume of the heart?

    <p>Heart rate</p> Signup and view all the answers

    What is the difference between absolute and relative refractory periods in cardiac muscle?

    <p>The absolute refractory period is when the heart cannot be stimulated to contract at all, while the relative refractory period is a period when the heart can only be stimulated by a very strong signal.</p> Signup and view all the answers

    Which of the following is NOT a factor that can cause a high pulse pressure?

    <p>High diastolic blood pressure with normal systolic blood pressure</p> Signup and view all the answers

    Compliance of the arterial tree is directly related to the level of vasoconstriction?

    <p>True</p> Signup and view all the answers

    Why is mean arterial pressure not simply the average of systolic and diastolic pressure at rest?

    <p>Mean arterial pressure accounts for the proportion of time spent in diastole, which typically lasts longer than systole. This means that diastole contributes more to the overall average pressure than systole.</p> Signup and view all the answers

    What is the role of the heart's right atrium in regulating blood flow?

    <p>The heart's right atrium receives blood from the body's peripheral veins. Its pressure influences the ease with which blood flows back into the heart, influencing the overall cardiac output.</p> Signup and view all the answers

    Explain why the sympathetic nervous system is able to increase the contractile force of cardiac muscle?

    <p>The sympathetic nervous system stimulates beta-adrenergic receptors in the heart, leading to an increase in intracellular calcium ions which increases the overall contractility of the cardiac muscle.</p> Signup and view all the answers

    Which of the following describes the intrinsic beat rate of the Purkinje fibers?

    <p>15-40 beats per minute</p> Signup and view all the answers

    What are the two neurotransmitters released by the sympathetic and parasympathetic nervous systems to the heart?

    <p>The sympathetic nervous system releases norepinephrine (NE) and the parasympathetic nervous system releases acetylcholine (ACh).</p> Signup and view all the answers

    Match the following terms with their cardiovascular definitions?

    <p>Tachycardia = Faster than normal heart rate at rest Bradycardia = Slower than normal heart rate at rest Preload = A measure of the tension on the heart muscle before it contracts Afterload = The pressure the heart must overcome to eject blood into the aorta Stroke volume = The amount of blood ejected from the heart with each beat</p> Signup and view all the answers

    Explain the concept of total peripheral resistance (TPR) in the cardiovascular system.

    <p>Total peripheral resistance (TPR) represents the overall resistance encountered by blood as it flows through the systemic circulatory system. It reflects the collective resistance of all the arteries and arterioles within the body.</p> Signup and view all the answers

    Which of the following is NOT a factor that contributes to increased total peripheral resistance?

    <p>Increased diameter of blood vessels</p> Signup and view all the answers

    What is the difference between preload and afterload in the cardiovascular system?

    <p>Preload refers to the initial stretching force on the cardiac muscle fibers before contraction, influenced by the amount of blood filling the heart during diastole. Afterload represents the resistance the heart must overcome to eject blood during systole, mainly influenced by the pressure in the aorta.</p> Signup and view all the answers

    The circulatory system is a closed system with no beginning or end.

    <p>True</p> Signup and view all the answers

    Which of the following is NOT a function of the heart?

    <p>To produce red blood cells</p> Signup and view all the answers

    What is the name of the valve located between the right atrium and the right ventricle?

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

    What is the name of the valve located between the left atrium and the left ventricle?

    <p>Mitral valve</p> Signup and view all the answers

    What are the two main types of valves found in the heart?

    <p>Atrioventricular (AV) valves and semilunar valves.</p> Signup and view all the answers

    The heart is a single organ, which means it only acts as one unit during each heartbeat.

    <p>False</p> Signup and view all the answers

    The specialized junctions between cardiac muscle cells are called ______ .

    <p>intercalated discs</p> Signup and view all the answers

    The contraction of the papillary muscles and chordae tendinae helps prevent backflow of blood from the ventricles into the atria.

    <p>True</p> Signup and view all the answers

    What is the primary function of the semilunar valves?

    <p>To prevent the backflow of blood from the arteries into the ventricles.</p> Signup and view all the answers

    Which of the following is NOT a factor that contributes to the opening and closing of heart valves?

    <p>Gravity</p> Signup and view all the answers

    Which of the following is TRUE regarding blood flow distribution at rest?

    <p>The brain receives the highest percentage of blood flow.</p> Signup and view all the answers

    What is the primary function of the circulatory system?

    <p>To transport blood throughout the body, delivering oxygen and nutrients to tissues and removing waste products.</p> Signup and view all the answers

    The heart rate is the same as the number of heartbeats per minute.

    <p>True</p> Signup and view all the answers

    Study Notes

    Cardiovascular System (Week 4)

    • Cardiac Anatomy and Function: Blood flows from the vena cava through the heart and into the aorta. This includes the right atrium, tricuspid valve, right ventricle, pulmonary valve (semilunar), pulmonary artery, lungs, pulmonary vein, left atrium, mitral valve, left ventricle, and aortic valve (semilunar).

    • Cardiac Muscle Histology: Cardiac and skeletal muscle are both striated with actin and myosin. However, cardiac muscle has intercalated discs, specialized connections that facilitate rapid electrical signal transmission between cells.

    • Intercalated Discs: These structures allow for rapid communication and ion diffusion between cardiac muscle cells, essential for coordinated heart contractions.

    • Papillary Muscles and Chordae Tendinae: Papillary muscles, attached to the atrioventricular (AV) valves via chordae tendinae, prevent the valves from bulging back into the atria during ventricular contraction, thus preventing regurgitation.

    • Semilunar vs. AV Valves: AV valves are thinner than semilunar valves, which are stronger to withstand the higher velocity of blood flow. Semilunar valves function passively due to high pressure in arteries, avoiding the need for chordae tendinae for support.

    Blood Flow Distribution at Rest

    • Brain (15%): Absolute volume remains constant, but percentage decreases during exercise.

    • Coronary Arteries (5%): Absolute volume increases proportionally to exercise as the heart's working demands more blood. Percentage remains at 5% during exercise.

    • Kidneys (25%): Absolute volume remains constant at rest. Percentage remains at 25% during exercise.

    • Other Organs (e.g. GI Tract, Skeletal Muscle, Skin): Distribution percentages change substantially when exercising.

    • Resting vs. Exercise blood flow: Blood flow to exercising muscle increases dramatically.

    Cardiac Muscle Contractility

    • Plateau in Action Potential: Cardiac muscle action potentials exhibit a plateau phase due to L-type calcium channels activation, which slows repolarization to facilitate prolonged contraction and prevents tetanus. Skeletal muscle action potentials do not exhibit this plateau.

    • Slow Calcium Channels: The prolonged plateau in cardiac muscle action potentials, unlike skeletal muscle, is primarily due to calcium channels, and this differs from skeletal muscles

    • Conduction Velocity: Purkinje fibers have much faster conduction velocities compared to cardiac muscle fibers. This ensures rapid signal transmission throughout the heart for coordinated contractions.

    • Refractory Periods: Cardiac muscle has both absolute and relative refractory periods. The absolute refractory period prevents the heart from being stimulated again while contracting, ensuring a single contraction per signal. Relative refractory period, in which the heart can potentially contract if the signal is strong enough, prevents tetanus.

    • Extracellular Calcium Concentration: Calcium from the extracellular fluid is crucial for cardiac muscle contraction, unlike skeletal muscle where calcium is primarily from sarcoplasmic reticulum.

    Cardiac Cycle

    • Heart Rate, Action Potential & Cardiac Cycle: Increased heart rate = shorter action potential plateau, decreased time in systole, and increased ratio of systole to diastole.

    • Atrial Systole: Ventricular filling occurs during atrial systole (contraction) due to increased pressure in the atria pushing blood into the ventricles.

    • Ventricular Filling, Ejection & Isometric Contraction: Ventricular pressures gradually increase, opening AV valves, causing rapid filling of ventricles. Isometric contraction occurs before expulsion.

    • Ventricular Pressure: The period of rapid ejection is the time when blood pressure in the ventricles is the greatest, causing the highest ejection volume.

    • Preload and Afterload: Preload refers to the degree of filling, while afterload refers to the pressure the ventricles must overcome to contract and eject blood. Both preload and afterload influence ventricular volume and blood pressure throughout the cardiac cycle.

    Cardiac Conduction System

    • Sinoatrial Node (SA Node): The heart's natural pacemaker.

    • Other pacemaker cells: Atrioventricular (AV) node and Purkinje fibers contribute to heart rate as well.

    • Automaticity: The intrinsic ability of cardiac cells to spontaneously depolarize and generate action potentials without external stimulation.

    • Sympathetic and Parasympathetic Nervous System: Sympathetic innervation increases heart rate, and parasympathetic innervation slows heart rate through the vagus nerve by releasing neurotransmitters.

    Heart Rate Terminology

    • Tachycardia: A heart rate faster than normal at rest

    • Bradycardia: A heart rate slower than normal at rest

    • Heart rate, exercise and pathology: Heart rate increases during exercise but is not generally considered a sign of underlying pathology.

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    Description

    This quiz covers essential topics related to the cardiovascular system, focusing on cardiac anatomy and function, as well as the histology of cardiac muscle. It highlights the roles of intercalated discs, papillary muscles, and chordae tendinae in heart physiology. Test your understanding of these crucial concepts in Week 4 of your studies.

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