Cardiovascular System Week 4
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Trace the path of a drop of blood as it travels from the vena cava through the heart and into the aorta. This should include the chambers, and the valves it passes through.

Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve (Semilunar) → Pulmonary Artery → Lungs → Pulmonary Vein → Left Atrium → Mitral Valve → Left Ventricle → Aortic Valve (Semilunar) → Aorta

Compare and contrast the histology of cardiac muscle to skeletal muscle. Which of the following statements are true? (Select all that apply)

  • Skeletal muscle has splitting, syncytial arrangement, while cardiac muscle does not.
  • Both cardiac and skeletal muscles are striated with actin and myosin. (correct)
  • Cardiac muscle does not have intercalated discs, while skeletal muscle does.
  • Cardiac muscle has intercalated discs, while skeletal muscle does not. (correct)

Describe the function of intercalated discs in relation to electrical conduction within the heart.

Intercalated discs facilitate rapid diffusion of ions between cardiac muscle cells, enabling quick and coordinated spread of electrical impulses for efficient heart contraction.

Describe the function of the papillary muscles and chordae tendinae. Which of the following statements are true? (Select all that apply)

<p>Papillary muscles attach to AV valves by chordae tendinae. (A), Chordae tendinae prevent bulging of the AV valves towards the atria, preventing regurgitation. (C), Papillary muscles prevent bulging of the AV valves towards the atria, preventing regurgitation. (D)</p> Signup and view all the answers

Compare the properties of the semilunar valves and the AV valves. Which of the following statements are true? (Select all that apply)

<p>Semilunar valves are built stronger than AV valves. (A), The velocity of blood flow is faster through semilunar valves due to their stronger structure. (B), AV valves function passively, depending on the pressure gradient between the ventricles and atria. (E)</p> Signup and view all the answers

At rest, what percentage of blood flow is directed to the brain?

<p>15% (A)</p> Signup and view all the answers

At rest, what percentage of blood flow is directed to the skeletal muscles?

<p>25% (C)</p> Signup and view all the answers

During cold temperatures, the body experiences vasodilation to conserve heat.

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

Which of the following are TWO mechanisms that cause the plateau in the action potential in cardiac muscle? (Select all that apply)

<p>Decreased permeability for potassium ions in cardiac muscle. (A), Additional activation of L-type calcium channels in cardiac muscle. (B)</p> Signup and view all the answers

The conduction velocity of signals through Purkinje fibers is much slower than the conduction velocity through cardiac muscle fibers.

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

Which of the following statements is TRUE about relative refractory periods in cardiac muscle?

<p>The heart can be stimulated to contract only by an especially strong signal during the relative refractory period. (C)</p> Signup and view all the answers

Why is extracellular calcium concentration more relevant for cardiac muscle contraction compared to skeletal muscle contraction?

<p>Cardiac muscle relies primarily on extracellular calcium stores, while skeletal muscle relies on intracellular calcium. (A)</p> Signup and view all the answers

During a period of increased heart rate, what changes occur in the duration of the action potential plateau and the duration of systole?

<p>Both action potential plateau and systole duration decrease. (D)</p> Signup and view all the answers

Explain what the Frank-Starling mechanism encompasses.

<p>The Frank-Starling mechanism describes the relationship between the amount of blood filling the heart (preload) and the strength of its contraction. Greater preload results in stronger contractions due to increased stretch of cardiac muscle fibers, leading to greater stroke volume.</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 impulse originates at the SA node and travels along internodal pathways, reaching the AV node. From the AV node, the signal passes through the AV bundle, branching into bundle branches and eventually reaching the Purkinje fibers, which distribute the impulse to the ventricular muscle.</p> Signup and view all the answers

Explain the concept of automaticity in the context of the heart’s electrical activity.

<p>Automaticity refers to the heart’s inherent ability to generate its own electrical impulses. This is essential for maintaining a regular heart rhythm and contraction even in the absence of external stimulation.</p> Signup and view all the answers

What is the intrinsic heart rate, and what factors influence it?

<p>The intrinsic heart rate is the rate the heart beats at when it is not being influenced by the autonomic nervous system. It’s typically around 70 to 90 beats per minute. It is affected by factors like temperature, hormones, and medications, but primarily regulated by the autonomic system.</p> Signup and view all the answers

What are the two main branches of the autonomic nervous system that influence heart function, and what effect does each have on heart rate?

<p>Sympathetic: increases heart rate; Parasympathetic: decreases heart rate (B)</p> Signup and view all the answers

What is the main neurotransmitter released by the parasympathetic nervous system that influences heart rate?

<p>Acetylcholine (Ach) is the neurotransmitter released by the parasympathetic nervous system, primarily through the vagus nerve, to slow down heart rate.</p> Signup and view all the answers

Does tachycardia always indicate an underlying health problem?

<p>No (A)</p> Signup and view all the answers

What is the primary function of papillary muscles in relation to the heart valves?

<p>They maintain tension on the chordae tendinae. (D)</p> Signup and view all the answers

Which statement accurately describes the difference between semilunar valves and AV valves?

<p>AV valves require chordae tendinae to function. (A)</p> Signup and view all the answers

What feature of cardiac muscle cells contributes to their ability to communicate quickly?

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

How does blood distribution to the brain change during exercise?

<p>It remains constant in absolute volume but decreases as a percentage. (D)</p> Signup and view all the answers

What is the primary role of the coronary arteries during periods of exercise?

<p>To increase blood flow proportionately to meet myocardial demands. (A)</p> Signup and view all the answers

What unique structural feature distinguishes cardiac muscle fibers from skeletal muscle fibers?

<p>Presence of intercalated discs (B)</p> Signup and view all the answers

During resting conditions, approximately what percentage of blood flow is directed to the kidneys?

<p>25% (C)</p> Signup and view all the answers

What feature of semilunar valves is crucial to their function?

<p>They are strengthened to withstand mechanical abrasion. (B)</p> Signup and view all the answers

What is the role of L-type calcium channels in cardiac muscle action potentials?

<p>They prolong depolarization by allowing greater influx of Na+ and Ca2+. (B)</p> Signup and view all the answers

How do Purkinje fibers compare to cardiac muscle fibers in terms of signal conduction?

<p>Purkinje fibers conduct signals significantly faster than cardiac muscle fibers. (A)</p> Signup and view all the answers

What defines the absolute refractory period in cardiac muscle?

<p>The heart cannot be stimulated to contract at all. (D)</p> Signup and view all the answers

During exercise, how does the body primarily respond to manage heat?

<p>By vasodilation to eliminate excess heat. (B)</p> Signup and view all the answers

What happens to potassium ion permeability during cardiac muscle action potentials?

<p>Potassium permeability decreases to prolong depolarization. (C)</p> Signup and view all the answers

What is the primary source of calcium for cardiac muscle contraction?

<p>It is derived from extracellular fluid. (D)</p> Signup and view all the answers

How does the cardiac cycle change with an increased heart rate?

<p>Duration of diastole remains constant and systole decreases. (D)</p> Signup and view all the answers

What distinguishes the relative refractory period from the absolute refractory period?

<p>The heart can respond only to strong stimuli in the relative refractory period. (B)</p> Signup and view all the answers

What heart rate range typically indicates that the heart is functioning normally?

<p>70 to 90 beats per minute (C), 70 to 90 beats per minute (D)</p> Signup and view all the answers

Which neurotransmitter is released by sympathetic nerves to increase the heart's rate and contractility?

<p>Norepinephrine (NE) (B)</p> Signup and view all the answers

Which of the following disturbances indicates parasympathetic nervous system stimulation?

<p>Decreased heart rate below 70 beats per minute (A)</p> Signup and view all the answers

How does the sympathetic nervous system increase cardiac contractility?

<p>Through beta adrenergic receptor stimulation (C)</p> Signup and view all the answers

What condition is known as a slower than normal heart rate at rest?

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

What is the role of afterload in the heart's function?

<p>It refers to the pressure the ventricles must overcome to eject blood. (A)</p> Signup and view all the answers

Which of the following scenarios indicates a higher afterload for the ventricles?

<p>Blood pressure of 140/90 (B)</p> Signup and view all the answers

How does increased afterload affect the ventricles?

<p>It requires the ventricles to work harder. (C)</p> Signup and view all the answers

What physiological basis does the Frank-Starling mechanism rely on?

<p>Increased preload leading to enhanced contractility. (D)</p> Signup and view all the answers

Which structure has the fastest intrinsic rhythmical rate in the heart?

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

What is the intrinsic heart rate when the heart is not affected by external nervous inputs?

<p>60-80 beats per minute (A)</p> Signup and view all the answers

What characterizes ectopic beats in the heart?

<p>They arise from non-sinoatrial node regions. (C)</p> Signup and view all the answers

Which statement about the conduction system of the heart is true?

<p>Electrical conduction starts at the sinoatrial node. (B)</p> Signup and view all the answers

What change occurs to the time spent in diastole when heart rate increases?

<p>Decreased time in diastole (B)</p> Signup and view all the answers

How does atrial contraction affect ventricular filling?

<p>It contributes approximately 20% to ventricular filling (B)</p> Signup and view all the answers

What occurs during isovolumetric contraction of the heart?

<p>Pressure in the ventricles rises to overcome arterial pressure (B)</p> Signup and view all the answers

Which statement best describes the ejection fraction and its normal value at rest?

<p>The ejection fraction is the fraction of EDV that is ejected; normal is 60% (C)</p> Signup and view all the answers

What differentiates the 'period of rapid ejection' from the 'period of slow ejection'?

<p>Rapid ejection has the greatest pressure and blood flow (A)</p> Signup and view all the answers

During the cardiac cycle, how do the pressures in the right and left ventricles compare during systole?

<p>Right ventricular pressures are about 1/6th that of the left (D)</p> Signup and view all the answers

What role does preload play in the cardiac cycle?

<p>It represents end diastolic pressure when the ventricle is filled (A)</p> Signup and view all the answers

What initiates the 'period of rapid filling of the ventricles'?

<p>Increased atrial pressure pushing AV valves open (A)</p> Signup and view all the answers

Flashcards

Blood flow path through the heart

Blood travels from vena cava to right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary artery, lungs, pulmonary vein, left atrium, mitral valve, left ventricle, aortic valve, and finally, aorta.

Cardiac vs. Skeletal Muscle

Both cardiac and skeletal muscle are striated, but cardiac muscle has intercalated discs and a syncytial arrangement.

Intercalated Discs

Specialized connections between cardiac muscle cells that allow rapid ion diffusion, enabling coordinated heart contractions.

Papillary Muscles and Chordae Tendineae

These structures prevent the AV valves from bulging into the atria during ventricular contraction, preventing backflow.

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Semilunar vs. AV valves

Semilunar valves (aortic and pulmonary) are stronger and function passively due to high arterial pressure, while AV valves (tricuspid and mitral) are thinner and need chordae tendineae to prevent backflow.

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Brain Blood Flow (Rest)

About 15% of blood flow goes to the brain at rest, which remains relatively constant.

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Coronary Blood Flow (Rest)

About 5% of total blood flow goes to coronary arteries. This increases proportionally with exercise.

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Kidney Blood Flow

About 25% of blood flow goes to kidneys at rest, and it's a key site for adjusting vascular resistance.

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GI Tract Blood Flow (Rest)

About 25% of blood flow goes to GI tract at rest; significantly reduced during exercise.

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Skeletal Muscle Blood Flow

About 25% of blood flow goes to skeletal muscle at rest, and this increases dramatically during exercise.

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Skin Blood Flow

About 5% of blood flow goes to skin at rest; changes with temperature, vasoconstricting with cold and initially with exercise; vasodilating with heat and during exercise.

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Cardiac Muscle Action Potential Plateau

Cardiac muscle action potentials have a plateau due to calcium channel activation and decreased potassium perm.

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Slow Calcium Channels

Allow prolonged depolarization in cardiac muscle causing the plateau in its action potential.

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Purkinje Fibers Conduction

Conduction in Purkinje fibers is much faster than in normal cardiac muscle fibers, ensuring rapid spread of electrical signals throughout the heart.

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Absolute Refractory Period

Period during which the heart cannot be stimulated to contract.

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Relative Refractory Period

Period where a stronger than normal signal is required to stimulate a heart contraction.

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Extracellular Calcium and Contraction

Calcium for cardiac muscle contraction comes more from extracellular fluid than the sarcoplasmic reticulum.

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Heart Rate, Cardiac Cycle, and Action Potential

Increased heart rate leads to a shorter action potential plateau, shorter systole, shorter diastole, and increases the ratio of systole to diastole.

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Ejection Fraction

Percentage of end-diastolic volume ejected; a measure of heart's pumping efficiency.

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Right Ventricular Pressure

Considerably lower than left ventricular pressure during systole.

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Preload

Ventricular stretch/filling pressure at the end of diastole, impacting contractile strength.

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Afterload

Resistance the ventricles must overcome to pump blood into the circulation.

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Frank-Starling Mechanism

Greater stretch of the heart (e.g., blood volume) leads to stronger contraction and thus larger stroke volume; increased atrial stretch also increases heart rate.

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Conduction System Pathway

Electrical signals travel from SA node to internodal pathways, AV node, bundle, bundle branches, and Purkinje fibers to the ventricles.

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Intrinsic Heart Rate

Heart's rate when not influenced by autonomic nervous system; about 70-90 bpm.

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Sympathetic Nerves and Heart

Sympathetic nerves affect all parts of the heart increasing heart rate, conduction, and contractile force.

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Parasympathetic Nerves and Heart

Parasympathetic nerves primarily impact the SA node and AV junction, decreasing heart rate.

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Vagus Nerve

The parasympathetic nerve supplying the heart.

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Autonomic Neurotransmitters

Sympathetic nerves release norepinephrine; parasympathetic release acetylcholine, which slow the heart.

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Sympathetic Effect on Contractility

Sympathetic stimulation leads to increased calcium levels, causing greater cardiac muscle contractile force.

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Heart Blood Flow Path

The journey of a blood droplet from the vena cava to the aorta, passing through heart chambers and valves: right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary artery, lungs, pulmonary vein, left atrium, mitral valve, left ventricle, aortic valve, aorta.

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Cardiac Muscle: Unique Features

Cardiac muscle differs from skeletal muscle by having intercalated discs, which allow rapid communication between cells and a syncytial arrangement, causing the heart to contract as a unit.

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What do papillary muscles and chordae tendineae do?

They prevent the atrioventricular (AV) valves from bulging back into the atria during ventricular contraction, stopping blood from flowing backwards.

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What's the key difference between semilunar and AV valves?

Semilunar valves, like aortic and pulmonary, are stronger and function passively due to high blood pressure in arteries. AV valves, like tricuspid and mitral, are thinner and need chordae tendineae to assist with closure.

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Blood Flow to the Brain at Rest

Approximately 15% of blood flow goes to the brain at rest, and this volume stays relatively constant even during exercise.

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Blood Flow to Coronary Arteries at Rest

Around 5% of total blood flow goes to coronary arteries at rest. This percentage remains constant during exercise, but the absolute blood volume increases.

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Blood Flow to Kidneys at Rest

At rest, 25% of blood flow is directed to the kidneys. This area plays a crucial role in regulating blood pressure, both at rest and during exercise.

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Blood Flow to Skeletal Muscles at Rest

Skeletal muscles receive about 25% of blood flow at rest. This increases dramatically during exercise, as working muscles need more oxygen and nutrients.

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Vasoconstriction in Cold

Blood vessels narrow, reducing blood flow to the skin surface, preserving core body heat.

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Vasoconstriction During Exercise (Initially)

Blood vessels in the skin briefly constrict during exercise to redirect blood to working muscle.

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Vasodilation in Heat

Blood vessels widen, allowing more blood flow to the skin surface, releasing heat.

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Slow Calcium Channels in Cardiac Muscle

These channels open slowly and longer in cardiac muscle than in skeletal muscle, promoting longer depolarization and creating the action potential plateau.

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Cardiac Muscle Refractory Periods

Absolute refractory period prevents any contraction during a particular time, while relative refractory period requires a stronger than normal stimulus to trigger a contraction.

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Extracellular Calcium for Cardiac Muscle

Cardiac muscle relies more on calcium from extracellular fluid, rather than the sarcoplasmic reticulum for contraction.

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Relationship of Heart Rate and Cardiac Cycle

Increased heart rate means a shorter action potential plateau, a shorter cardiac cycle with shorter systole and diastole, and an increased relative duration of systole.

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Normal Heart Rate

A resting heart rate typically falls between 70 and 90 beats per minute.

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Sympathetic Nervous System and Heart Rate

Increased sympathetic nervous system activity leads to a faster heart rate.

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Parasympathetic Nervous System and Heart Rate

Increased parasympathetic nervous system activity leads to a slower heart rate.

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Tachycardia

A faster than normal heart rate at rest.

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Bradycardia

A slower than normal heart rate at rest.

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Increased heart rate

A faster heart rate leads to a shorter period of ventricular contraction (systole) and a shorter period of ventricular relaxation (diastole).

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What happens to ventricular volume during diastole?

Ventricular volume increases during diastole as blood flows from the atria into the ventricles.

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Ventricular filling

The process of blood flowing into the ventricles during diastole. It is divided into two phases: a rapid filling phase and a slower filling phase.

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What is the ejection fraction?

A measurement of the heart's pumping efficiency. It represents the percentage of blood ejected from the ventricle with each heartbeat.

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What is preload?

The amount of stretch of the heart muscle at the end of diastole. It is determined by the volume of blood filling the ventricle.

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What is afterload?

The resistance the ventricle must overcome to eject blood into the aorta.

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Compare right ventricular pressure to left ventricular pressure.

The right ventricle generates significantly lower pressure compared to the left ventricle during systole. This is because the right ventricle only needs to pump blood to the lungs, while the left ventricle pumps blood throughout the entire body.

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Atrial contraction role

The atria contract just before the ventricles to provide an extra push of blood into the ventricle before ventricular contraction. This accounts for about 20% of ventricular filling.

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Higher Afterload

Means the ventricles need to work harder to pump blood, requiring more energy.

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SA Node

The 'pacemaker' of the heart. It initiates the electrical impulse that triggers heart contraction.

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AV Node

A gatekeeper that slows down the electrical impulse before it reaches the ventricles.

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Automaticity

The heart's ability to generate its own electrical impulses, allowing it to beat independently of the nervous system.

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Ectopic Beats

Heartbeats originating from a site other than the SA node. They're like extra, irregular beats.

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Study Notes

Cardiovascular System (Week 4)

  • Cardiac Anatomy and Function: Blood travels from the vena cava through the heart to the aorta, passing through specific chambers and valves. The path includes the right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary artery, lungs, pulmonary vein, left atrium, mitral valve, left ventricle, and aortic valve.

Cardiac Muscle Histology

  • Cardiac vs. Skeletal Muscle: Both are striated with actin and myosin but cardiac muscle has intercalated discs, which are essential for electrical conductivity.

Intercalated Discs

  • Electrical Conduction: These discs facilitate rapid ion diffusion and communication between cardiac muscle cells enabling coordinated contractions.

Papillary Muscles and Chordae Tendinae

  • AV Valve Function: Papillary muscles, connected to the AV valves via chordae tendinae, prevent valve inversion during ventricular contraction, thus preventing backflow into the atria.

Semilunar Valves vs. AV Valves

  • Structural Differences: Semilunar valves are stronger and have faster blood flow; they are passive structures and don't require chordae tendinae
  • AV Valve Function: These valves are thinner than semilunar valves, preventing backflow into the atria.

Blood Flow Distribution at Rest

  • Brain: ~15% of blood flow
  • Coronary Arteries: ~5% of blood flow, crucial for cardiac muscle function. This percentage remains constant during exercise.
  • Kidneys: ~25% of blood flow
  • Other Sites: Other regions of the body receive proportionate blood flow, adjusting during activity and demand.

Cardiac Muscle Contractility

  • Plateau in Action Potential: Cardiac muscle action potentials exhibit a plateau phase due to a prolonged influx of calcium ions. This contrasts with skeletal muscle's faster action potential.

Cardiac Muscle Fiber Conduction

  • Velocity: Purkinje fibers conduct signals much faster than other cardiac muscle fibers for efficient heart contraction.

Cardiac Contraction and Refractory Periods

  • Absolute Refractory Period: During this period, the heart cannot be stimulated to contract.
  • Relative Refractory Period: The heart can be stimulated, but only by stronger than normal stimuli.

Extracellular Calcium

  • Cardiac Muscle Contraction: Maintaining sufficient extracellular calcium is vital for cardiac muscle contraction as it's derived from that source.

Cardiac Cycle

  • Heart Rate, Action Potential, and Cycle Duration: Increased heart rate shortens the plateau phase of the action potential and reduces the time spent in ventricular systole, allowing more time for diastole and filling.
  • Preload: End-diastolic pressure reflecting the degree of tension on the heart before ventricular contraction.
  • Afterload: Resistance in the arterial system that ventricular pressure must overcome. Higher afterload means greater pressure required for pumping.

Conduction System

  • Conduction Pathway: Electrical impulses are conducted in a specific pathway through nodes and fibers to orchestrate the heartbeat. The path starts at the sinoatrial (SA) node, then travels through specific pathways leading into the ventricles.

Heart Rate Terminology

  • Tachycardia: Faster than normal resting heart rate.
  • Bradycardia: Slower than normal resting heart rate.

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Description

Explore the intricacies of the cardiovascular system in this Week 4 quiz. Delve into cardiac anatomy, muscle histology, and the function of essential structures such as intercalated discs and papillary muscles. Test your understanding of how blood flows through the heart and the role of valves in maintaining proper circulation.

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