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Questions and Answers
What is the term used to describe the amount of blood remaining in the ventricle at the end of systole?
What is the term used to describe the amount of blood remaining in the ventricle at the end of systole?
What is the name of the relationship between the amount of myocardial stretch and the force of contraction?
What is the name of the relationship between the amount of myocardial stretch and the force of contraction?
What is the primary factor that influences the volume of blood returned to the right atrium?
What is the primary factor that influences the volume of blood returned to the right atrium?
Which of the following factors will increase contractility?
Which of the following factors will increase contractility?
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What is the relationship between the length of ventricular diastole and end-diastolic volume?
What is the relationship between the length of ventricular diastole and end-diastolic volume?
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What is the effect of a greater end-diastolic volume (EDV) on stroke volume?
What is the effect of a greater end-diastolic volume (EDV) on stroke volume?
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What is the term for the amount of blood ejected from the ventricle with each heartbeat?
What is the term for the amount of blood ejected from the ventricle with each heartbeat?
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What is the approximate distance between the base and apex of the heart?
What is the approximate distance between the base and apex of the heart?
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Which of the following factors would likely reduce stroke volume?
Which of the following factors would likely reduce stroke volume?
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Where is the base of the heart located?
Where is the base of the heart located?
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What is the approximate distance between the apex of the heart and the left side of the sternum?
What is the approximate distance between the apex of the heart and the left side of the sternum?
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Regarding the heart, what is the relationship between the 3rd costal cartilage and the base?
Regarding the heart, what is the relationship between the 3rd costal cartilage and the base?
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What is the approximate distance between the apex of the heart and the 5th intercostal space?
What is the approximate distance between the apex of the heart and the 5th intercostal space?
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What is the function of the cardiovascular system?
What is the function of the cardiovascular system?
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Which of the following best describes the location of the heart in relation to the sternum?
Which of the following best describes the location of the heart in relation to the sternum?
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What are the two main circuits that the heart pumps blood through?
What are the two main circuits that the heart pumps blood through?
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What is the duration of atrial systole at a heart rate of 75 beats per minute?
What is the duration of atrial systole at a heart rate of 75 beats per minute?
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During which phase of the cardiac cycle are all four chambers relaxed?
During which phase of the cardiac cycle are all four chambers relaxed?
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Which phase of the cardiac cycle is characterized by the closure of the AV valves but not enough pressure to open the semilunar valves?
Which phase of the cardiac cycle is characterized by the closure of the AV valves but not enough pressure to open the semilunar valves?
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What is happening during atrial diastole?
What is happening during atrial diastole?
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During which phase of the cardiac cycle are all valves closed?
During which phase of the cardiac cycle are all valves closed?
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What event initiates the opening of the semilunar valves?
What event initiates the opening of the semilunar valves?
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Which phase of the cardiac cycle is characterized by the passive filling of atria while all valves are closed?
Which phase of the cardiac cycle is characterized by the passive filling of atria while all valves are closed?
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Which of these events occur during the Ventricular Ejection phase of the Cardiac Cycle? (Select all that apply)
Which of these events occur during the Ventricular Ejection phase of the Cardiac Cycle? (Select all that apply)
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Which of these components of the cardiac conduction system is not involved in the electrical excitation of the ventricles?
Which of these components of the cardiac conduction system is not involved in the electrical excitation of the ventricles?
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What is the primary function of the Purkinje fibers?
What is the primary function of the Purkinje fibers?
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Which statement BEST describes the role of the bundle of His in the cardiac conduction system?
Which statement BEST describes the role of the bundle of His in the cardiac conduction system?
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Why is it essential for the electrical signal to be delayed at the AV node before it reaches the ventricles?
Why is it essential for the electrical signal to be delayed at the AV node before it reaches the ventricles?
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Which of the following statements about the Purkinje fibers is TRUE?
Which of the following statements about the Purkinje fibers is TRUE?
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What is the significance of the left bundle branch being larger than the right bundle branch?
What is the significance of the left bundle branch being larger than the right bundle branch?
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If the SA node were to fail, what would be the likely outcome?
If the SA node were to fail, what would be the likely outcome?
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What is the purpose of the electrocardiogram (ECG or EKG)?
What is the purpose of the electrocardiogram (ECG or EKG)?
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Which of the following is NOT a characteristic of rapid depolarization in cardiac muscle?
Which of the following is NOT a characteristic of rapid depolarization in cardiac muscle?
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What is responsible for maintaining the plateau phase of an action potential in cardiac muscle?
What is responsible for maintaining the plateau phase of an action potential in cardiac muscle?
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What event is responsible for repolarization of the cardiac muscle cell?
What event is responsible for repolarization of the cardiac muscle cell?
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What is the main difference between cardiac muscle action potentials and skeletal muscle action potentials?
What is the main difference between cardiac muscle action potentials and skeletal muscle action potentials?
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Why does tetany not occur in cardiac muscle?
Why does tetany not occur in cardiac muscle?
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What is the function of slow calcium channels in cardiac muscle?
What is the function of slow calcium channels in cardiac muscle?
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What is the relationship between heart rate, stroke volume, and cardiac output?
What is the relationship between heart rate, stroke volume, and cardiac output?
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What is the primary function of the cardiac conducting system?
What is the primary function of the cardiac conducting system?
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What is the primary function of the papillary muscles during ventricular contraction?
What is the primary function of the papillary muscles during ventricular contraction?
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Which of the following is NOT a characteristic of the cardiac skeleton?
Which of the following is NOT a characteristic of the cardiac skeleton?
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What is the primary function of the semilunar valves?
What is the primary function of the semilunar valves?
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Which of the following is a potential cause of valvular heart disease?
Which of the following is a potential cause of valvular heart disease?
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Which of the following statements about the AV valves is TRUE?
Which of the following statements about the AV valves is TRUE?
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Cardiac regurgitation refers to:
Cardiac regurgitation refers to:
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What is the primary function of the cardiac skeleton?
What is the primary function of the cardiac skeleton?
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Which type of valve is characterized by having three half-moon-shaped cusps?
Which type of valve is characterized by having three half-moon-shaped cusps?
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Flashcards
Bundle branches
Bundle branches
The right and left pathways that conduct impulses in the heart.
Left bundle branch
Left bundle branch
The larger branch that transmits signals to the left ventricle.
Purkinje fibers
Purkinje fibers
Specialized fibers that conduct electrical impulses throughout the ventricles.
Action potentials
Action potentials
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Cardiac conduction system
Cardiac conduction system
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SA node
SA node
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AV node
AV node
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Electrocardiogram (ECG)
Electrocardiogram (ECG)
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End-Diastolic Volume (EDV)
End-Diastolic Volume (EDV)
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Ventricular Ejection
Ventricular Ejection
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End-Systolic Volume (ESV)
End-Systolic Volume (ESV)
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Stroke Volume
Stroke Volume
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Preload
Preload
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Frank-Starling Law
Frank-Starling Law
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Contractility
Contractility
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Factors Influencing ESV
Factors Influencing ESV
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Cardiac Cycle
Cardiac Cycle
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Systole
Systole
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Diastole
Diastole
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Atrial Systole
Atrial Systole
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Ventricular Systole
Ventricular Systole
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Isovolumetric Contraction
Isovolumetric Contraction
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Isovolumetric Relaxation
Isovolumetric Relaxation
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Cardiac Cycle Duration at 75 bpm
Cardiac Cycle Duration at 75 bpm
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AV Valves
AV Valves
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Semilunar Valves
Semilunar Valves
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Cardiac Skeleton
Cardiac Skeleton
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Papillary Muscles
Papillary Muscles
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Ventricular Contraction
Ventricular Contraction
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Backflow Prevention
Backflow Prevention
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Valvular Heart Disease (VHD)
Valvular Heart Disease (VHD)
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Bioprosthetic Valves
Bioprosthetic Valves
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Heart Location
Heart Location
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Heart Chambers
Heart Chambers
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Pulmonary Circuit
Pulmonary Circuit
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Systemic Circuit
Systemic Circuit
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Pericardium
Pericardium
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Heart Wall Layers
Heart Wall Layers
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Major Heart Vessels
Major Heart Vessels
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Arteriosclerosis
Arteriosclerosis
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Rapid Depolarization
Rapid Depolarization
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Plateau Phase
Plateau Phase
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Resting Potential
Resting Potential
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Repolarization
Repolarization
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Calcium Channels
Calcium Channels
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Tetany in Cardiac Muscle
Tetany in Cardiac Muscle
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Cardiac Output (CO)
Cardiac Output (CO)
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Heart Rate (HR)
Heart Rate (HR)
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Study Notes
Chapter 18: The Heart and Cardiovascular Function
- The cardiovascular system comprises the heart and blood vessels, which transport blood throughout the body.
- The heart is situated in the mediastinum, a region of the thoracic cavity between the lungs.
- The heart is positioned approximately behind the sternum, slightly to the left of center.
- The base of the heart is superior, and the apex is inferior and pointed.
- The heart's base is ~1.2 cm (0.5 in) to the left of center, and sits at the level of the 3rd costal cartilage.
- The apex of the heart is ~12.5 cm (5 in) from the base, and ~7.5 cm (3 in) to the left of the base, and sits at the 5th intercostal space.
Section 1: Structure of the Heart
- The heart is a two-sided pump with four chambers:
- Right atrium—receives blood from the systemic circuit.
- Right ventricle—pumps blood into the pulmonary circuit.
- Left atrium—receives blood from the pulmonary circuit.
- Left ventricle—pumps blood into the systemic circuit.
Section 1: Learning Outcomes
- Describe the heart's location, shape, four chambers, and pulmonary/systemic circuits.
- Describe the heart's location and general features.
- Describe the pericardium's structure and function, identify the heart wall layers, and describe cardiac muscle structures/functions.
- Describe the cardiac chambers and the heart's external anatomy.
- Describe the major vessels supplying the heart.
- Trace blood flow through the heart, identifying major blood vessels, chambers, and heart valves.
- Describe the relationship between AV and semilunar valves during a heartbeat.
- Define arteriosclerosis and its significance to health.
Module 18.1: The Heart Has Four Chambers That Pump...
- Cardiovascular system = heart and blood vessels transporting blood
- Heart—directly behind sternum
- Base—superior
- 1.2 cm (0.5 in) to left
- 3rd costal cartilage
- Apex—inferior, pointed tip
- 12.5 cm (5 in) from base
- 7.5 cm (3 in) to left
- 5th intercostal space
Module 18.2: The Heart Is Located in the Mediastinum...
- Mediastinum = space or region in thorax between the two pleural cavities (between the lungs)
Module 18.2: The Pericardium
- Pericardium = sac-like structure wrapped around the heart.
- Fibrous pericardium: Outermost layer; dense fibrous tissue extending to sternum and diaphragm
- Serous pericardium (2 layers): Outer parietal layer lines fibrous pericardium; inner serous layer covers the surface of the heart.
- Pericardial cavity: Space between serous layers; contains 15–50 mL of pericardial fluid secreted from serous membranes; lubricates heart movement.
- Pericarditis = inflammation of the pericardium
- Cardiac tamponade = excess accumulation of pericardial fluid.
Module 18.2: The Relationship Between Heart and Pericardium
- Push fist into partly inflated balloon
- Fist = heart
- Wrist = base of heart with great vessels
- Inside of balloon = pericardial cavity
Module 18.3: The Heart Wall Contains Concentric Layers...
- Heart wall has three layers:
- Fibrous pericardium: dense fibrous tissue and 2-layered serous pericardium.
- Epicardium: visceral layer of the serous pericardium
- Myocardium: middle layer; concentric layers of cardiac muscle; supporting blood vessels and nerves
- Endocardium: innermost layer; simple squamous epithelium (endothelium) inside heart and vessels. Cardiac muscle is continuous with endothelium in vessels and covers heart valves
Module 18.3: The Heart Wall—Cardiac Muscle
- Cardiac muscle cells are smaller than skeletal muscle cells (avg. 10–20 µm diameter; 50–100 µm length)
- Each cell has a single, centrally located nucleus.
- Intercalated discs—branching interconnections between cells; specialized intercellular connections.
- Only in heart; striated (from organized myofibrils and aligned sarcomeres)
- Almost totally dependent on aerobic metabolism (need oxygen) for energy
- Abundant mitochondria and myoglobin (stores O₂)
- Extensive capillaries
Module 18.3: Cardiac Muscle Tissue (continued)
- Intercalated discs: intertwined plasma membranes of adjacent cardiac muscle cells, attached by desmosomes and gap junctions.
- Gap junctions allow action potentials to travel from one cell to another allowing all interconnected cells to act as a functional syncytium.
Module 18.4: The Boundaries Between the Four Chambers...
- Visible on anterior surface: all four chambers, auricle of each atrium (expandable pouch), coronary sulcus (groove separating atria and ventricles), anterior interventricular sulcus (groove marking boundary between ventricles), ligamentum arteriosum (fibrous remnant of fetal connection between aorta and pulmonary trunk).
Module 18.5: The Heart Has an Extensive Blood Supply
- Coronary circulation—continuously supplies cardiac muscle with oxygen/nutrients
- Left and right coronary arteries arise from ascending aorta and fill when ventricles are relaxed (diastole)
- Myocardial blood flow may increase to nine times the resting level during maximal exertion.
Module 18.6: Internal Valves Control the Direction...
- Each side of heart has two chambers: an atrium (receives blood), ventricle (pumps blood out).
- Right and left atria are separated by the interatrial septum.
- Right and left ventricles are separated by the interventricular septum, much thicker.
Module 18.6: Heart Valves
- Atrioventricular (AV) valves—between each atrium and ventricle; allow one-way blood flow from atrium into ventricle.
- Semilunar valves—at exit from each ventricle; allow one-way blood flow from ventricle out into aorta or pulmonary trunk
Module 18.7: When the Heart Beats, the AV Valves...
- When ventricles are relaxed, they fill:
- AV valves—open
- Chordae tendineae—loose
- Semilunar valves—closed
- Blood pressure from pulmonary and systemic circuits keeps them closed.
Module 18.7: Valves Control Direction of Flow
- AV valves—closed when ventricles contract, preventing backflow into atria.
- Semilunar valves—open when ventricles contract, allowing blood to flow out of ventricles.
- Cardiac skeleton—flexible connective tissue frame with interconnected bands of dense connective tissue circling heart valves, stabilizing their positions and surrounding the aorta and pulmonary trunk.
Module 18.7: Valvular Heart Disease
- Valve function deteriorates until heart cannot maintain adequate blood flow.
- Congenital malformations or heart inflammation (carditis).
- Severe cases may require replacement with prosthetic valves (from pigs, cows).
Module 18.8: Arteriosclerosis Can Lead to Coronary Artery Disease
- Arteriosclerosis (arterio- artery + sclerosis, hardness): Thickening/toughening of arterial walls, contributing to about half of U.S. deaths.
- Coronary Artery Disease (CAD): Arterosclerosis of coronary vessels. Arteriosclerosis of brain arteries can lead to strokes.
- Atherosclerosis: formation of lipid deposits in arterial tunica media, and damage to endothelium.
- Fatty tissue mass (plaque) in vessel restricts blood flow.
- Risk factors for Arteriosclerosis include: age, male sex, high blood cholesterol levels, high blood pressure, and cigarette smoking.
Module 18.8: Atherosclerosis Treatment
- Replace damaged segment of vessel, compressing plaque with balloon angioplasty
- Catheter inserted past blockage: balloon inflated to press plaque against vessel wall and open vessel
- Most effective for small soft plaques
- Very low surgical mortality rate (about 1%)
- Very high success rate (>90%)
- Can be outpatient procedure.
Module 18.8: Coronary Artery Disease
- Areas of partial or complete blockage of coronary circulation reduce blood flow to the area (coronary ischemia)
- Usually caused by atherosclerosis in a coronary artery or associated blood clots (thrombi)
Module 18.9: The Cardiac Cycle Is a Complete Round...
- Cardiac cycle = period between start of one heartbeat and the next. Heart rate is the number of beats per minute.
- Two atria contract first to fill ventricles, then two ventricles contract to pump blood into pulmonary and systemic circuits.
- Cardiac cycle has two phases:
- Contraction (systole)—blood leaves the chamber
- Relaxation (diastole)—chamber refills
Module 18.9: Sequence of Contractions
- Atria contract together first (atrial systole): push blood into ventricles; ventricles relax (diastole) and fill.
- Ventricles contract together next (ventricular systole): push blood into pulmonary and systemic circuits; atria relax (diastole) and fill.
- Typical cardiac cycle lasts 800 msec.
Module 18.10: The Cardiac Cycle Creates Pressure...
- Phases of cardiac cycle (heart rate 75 bpm)
- Cardiac cycle begins—all four chambers relaxed (diastole; ventricles filling passively)
- Atrial systole (100 msec)—atria contract, finishing filling ventricles
- Isovolumetric relaxation (70 msec)—all valves closed; no volume change; blood passively filling atria
- Atrial diastole (270 msec)—continues until start of next cardiac cycle (ventricular systole)
- Ventricular systole—first phase (100 msec)—contracting ventricles push AV valves closed, not enough pressure to open semilunar valves. No volume change
- Ventricular systole—second phase (70 msec)—Increasing pressure opens semilunar valves; blood leaves ventricle (ventricular ejection)
- Ventricular diastole—early (70 msec)—Ventricles relax and their pressure drops, blood backflows closes semilunar valves
- Ventricular diastole—late (300 msec)—all chambers relaxed; AV valves open; ventricles fill passively to ~70%.
- Heart sounds: S₁ ("lubb"—when AV valves close, marks start of ventricular contraction); S₂ ("dupp"—when semilunar valves close), S₃ and S₄—very faint, rarely heard in adults (S₃ = blood flowing into ventricles; S₄ = atrial contraction)
Module 18.11: Cardiac Muscle Cell Contractions...
- Skeletal muscle: brief action potential, short twitch contraction, short refractory period, can summate twitches, tetanus occurs
- Cardiac muscle: long action potential, long contraction, prolonged period of Ca2+ influx, long refractory period, no tetanic contractions.
- Three stages of cardiac action potential: Rapid depolarization, Plateau, Repolarization
- Rapid depolarization: voltage-gated fast sodium channels open, massive, rapid Na+ influx.
- Plateau: fast sodium channels close, cell actively pumps Na+ out, voltage-gated slow calcium channels open (Ca2+ influx), plateau lasts ~175 msec.
- Repolarization: slow calcium channels close, slow potassium channels open, massive K+ efflux, rapid return to resting potential.
Module 18.12: Electrical Events of Pacemaker Cells…
- Cardiac output (CO) = amount of blood pumped from the left ventricle each minute
- Determined by heart rate (HR) and stroke volume (SV)
- Precisely adjusted to meet needs of tissues
- To calculate CO: Cardiac Output = HR × SV
- HR = number of contractions per minute; SV = volume of blood pumped out of ventricle per contraction
Module 18.12: Cardiac Conducting System
- Autorhythmicity = cardiac muscle's ability to contract at its own pace independent of neural or hormonal stimulation.
- Conducting system = network of specialized cardiac muscle cells (pacemaker and conducting) that initiate/distribute a stimulus to contract.
- Components of the conducting system: Sinoatrial node (SA node), Internodal pathways, Atrioventricular node (AV node), AV bundle and bundle branches, Purkinje fibers
Module 18.13: Normal and Abnormal Cardiac Activity...
- ECG or EKG: recording of heart's electrical activities from body surface assess performance of nodal, conducting, and contractile heart components.
- Abnormal heart pattern may appear if part of heart is damaged by a heart attack.
- Appearance of ECG pattern varies with placement and number of electrodes (leads).
Module 18.13: Explanation of ECG Features
- P wave = atrial depolarization, atria begin contracting ~25 msec after P wave starts.
- QRS complex = ventricular depolarization (larger wave due to larger ventricle muscle mass), ventricles begin contracting shortly after the R-wave peak, atrial repolarization also occurs but masked.
- T wave = ventricular repolarization
- P-R interval = period from start of atrial depolarization to start of ventricular depolarization (>200 msec may mean damage to conducting pathways or AV node complex.)
- Q-T interval = time for ventricles to undergo a full cycle (~300 msec), may be lengthened by electrolyte abnormalities, medications, conduction problems, coronary ischemia, myocardial damage.
Module 18.13: ECG and Arrhythmias
- Arrhythmia: abnormal patterns of cardiac electrical activity (seen in 5% of healthy people).
- Premature atrial contractions (PACs): normal atrial rhythm momentarily interrupted by a "surprise" atrial contraction.
- Paroxysmal atrial tachycardia (PAT): premature atrial contraction triggers a flurry of atrial activity, and heart rate jumps to about 180 bpm, with ventricles keeping the pace.
- Atrial fibrillation (AF): impulses move over atrial surface at up to 500 bpm, atria quiver, ventricular rate cannot follow (may remain normal), atria nonfunctional.
- Premature ventricular contractions (PVCs): Purkinje cell or ventricular myocardial cells depolarize prematurely.
- Ventricular Tachycardia (VT): four or more PVCs without intervening normal beats (usually indicates serious cardiac problems)
- Ventricular fibrillation (VF): ventricles quiver but cannot pump any blood, leading to cardiac arrest.
Module 18.14: The Intrinsic Heart Rate Can Be Altered...
- Pacemaker potential: gradual spontaneous depolarization in SA/AV nodes; cannot maintain stable resting membrane potential; membrane drifts toward threshold, triggering depolarization
- Parasympathetic influence: ACh from parasympathetic neurons open K+ channels; hyperpolarizes membrane, slows spontaneous depolarization, and lengthens repolarization.
- Sympathetic influence: norepinephrine binds to beta-1 receptors, increases rate of depolarization, and decreases repolarization.
- Resting heart rate varies with age, general health, and physical conditioning; normal range is 60-100 bpm.
- Bradycardia: heart rate is slower than normal (<60 bpm)
- Tachycardia: heart rate is faster than normal (>100 bpm)
- Cardiac centers of the medulla oblongata: contain cardioinhibitory and cardioacceleratory centers.
Module 18.15: Stroke Volume Depends on the Relationship…
- Stroke volume analogy (compared to a manual pump): amount pumped varies with pump handle movement, and amount of water is equivalent to stroke volume.
- End-diastolic volume (EDV) = ventricle blood volume at end of ventricular diastole.
- End-systolic volume (ESV) = ventricle blood volume at end of ventricular systole.
- Stroke volume = EDV - ESV
- Factors affecting stroke volume:
- EDV (amount of blood filling ventricle during diastole) influenced by venous return (amount of venous blood returned to right atrium), filling time, and preload (amount of myocardial stretch).
- Contractility (amount of force produced during contraction) influenced by sympathetic stimulation (epinephrine, norepinephrine), hormones, beta blockers, and calcium channel blockers.
- Afterload (ventricular tension required to open semilunar valves and empty) influenced by blood flow and vasoconstriction; afterload increases = stroke volume decreases.
Module 18.16: Cardiac Output is Regulated by Adjustments…
- Factors affecting cardiac output: cardiac output varies widely to meet metabolic demands, which can be adjusted through influencing heart rate or stroke volume.
- Heart failure: condition in which heart cannot meet demands of peripheral tissues.
Module 18.16: Cardiac Output Adjustment
- Factors affecting heart rate: exercise, muscular contractions, blood volume, blood flow, and atrial reflex. The atrial reflex involves adjustments in heart rate and in response to an increase in the venous return. When the walls of the right atrium are stretched, stretch receptors there stimulate sympathetic activity.
- Factors affecting stroke volume: autonomic nervous system (sympathetic and parasympathetic), hormones, preload (amount of myocardial stretch related to EDV), contractility (amount of force during contraction), and afterload (ventricular tension required to open semilunar valves (related to blood flow).
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Test your knowledge of cardiac physiology with this quiz focusing on key concepts like blood flow, ventricular function, and stroke volume. Each question challenges your understanding of the heart's structure and its physiological processes. Perfect for students and professionals alike!
