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Questions and Answers
What is the primary function of the heart in the cardiovascular system?
Where is the heart mainly located within the body?
Which layer of the heart is primarily responsible for its pumping action?
What does the fibrous pericardium do for the heart?
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What type of fluid is found in the pericardial cavity?
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Which structure of the heart lies at the base?
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What is the approximate average mass of the human heart?
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Which chamber of the heart faces the left lung?
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What is the primary function of the left side of the heart?
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What is the primary function of coronary arteries?
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What happens when there is a blockage in a coronary artery?
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Which structure carries deoxygenated blood from the systemic circulation to the heart?
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Which coronary artery supplies both ventricles?
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What is the role of the pulmonary arteries in the circulatory system?
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What condition is often associated with myocardial ischemia?
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Where does gas exchange primarily occur in relation to the circulatory system?
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What happens to the pressure of blood in the aorta when the heart relaxes?
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What is the role of autorhythmic fibers in the heart?
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Where is the sinoatrial (SA) node located?
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How do coronary arteries contribute to the circulatory system?
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What is the sequence of blood flow from the heart to the body tissues?
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What occurs during a myocardial infarction?
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What is the connection between coronary veins and coronary arteries?
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What describes the primary function of the venules in the circulatory system?
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What event initiates atrial systole?
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During which phase of the cardiac cycle do the ventricles contract?
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What does preload refer to in the context of heart function?
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Which law explains how the force of contraction is affected by the amount of blood in the ventricles during diastole?
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The QT-interval on an ECG represents which of the following?
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What is the result of an increased heart rate on ventricular diastole?
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What occurs during ventrical depolarization?
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How long does atrial systole last?
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Which of the following factors is NOT a determinant of end-diastolic volume (EDV)?
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What is the term for the volume of blood in each ventricle at the end of diastole?
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Positive inotropic agents affect myocardial contractility by doing what?
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What effect does the contraction of the ventricles have on the AV valves?
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The pressure that must be exceeded for blood ejection from the ventricles is referred to as what?
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Which of the following describes a consequence of increased venous return?
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What does the T wave in an ECG represent?
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What does the Frank-Starling law help to ensure between the right and left ventricles?
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Study Notes
Introduction
- The cardiovascular system consists of blood, blood vessels, and the heart.
- The heart pumps blood through an estimated 100,000 km of blood vessels.
- An average heart weighs 250-300 g.
- The heart is situated within the mediastinum between the lungs.
- Approximately two-thirds of the heart lies to the left of the midline.
- Due to its location between the rigid vertebral column and sternum, external chest compression can be used to force blood out of the heart.
Heart Orientation
- Apex: Points anteriorly, inferiorly, and to the left.
- Base: Points posteriorly, superiorly, and to the right.
- Anterior surface: Deep to the sternum and ribs.
- Inferior surface: Rests on the diaphragm.
- Right border: Faces the right lung.
- Left border (pulmonary border): Faces the left lung.
Pericardium
- The pericardium surrounds and protects the heart.
- It is composed of two layers:
- Fibrous pericardium: Outer layer, prevents overstretching and anchors the heart.
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Serous pericardium: Inner layer, composed of a parietal and visceral layer.
- The parietal layer: Lines the fibrous pericardium.
- The visceral layer: Covers the heart's outer surface.
- The pericardial cavity lies between the parietal and visceral layers and contains pericardial fluid, which reduces friction.
Layers of the Heart Wall
- The heart wall has three layers:
- Epicardium: Outermost layer, known as the visceral layer of the serous pericardium.
- Myocardium: Middle layer, composed of cardiac muscle tissue, responsible for the heart's pumping action.
- Endocardium: Innermost layer, provides a smooth lining for the heart chambers and covers the heart valves.
Chambers and Sulci of the Heart
- The heart has four chambers:
- Right atrium: Receives deoxygenated blood from the body.
- Right ventricle: Pumps deoxygenated blood to the lungs.
- Left atrium: Receives oxygenated blood from the lungs.
- Left ventricle: Pumps oxygenated blood to the body.
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Sulci: Grooves on the heart's surface that contain coronary blood vessels.
- Coronary sulcus: Groove that encircles the heart, separating the atria from the ventricles.
- Interventricular sulci: Grooves that separate the ventricles.
Systemic Circulation
- The left side of the heart pumps blood throughout the body, excluding the lungs.
- Blood is ejected from the left ventricle into the aorta, which then distributes blood to various systemic arteries supplying organs.
- Systemic arteries branch into arterioles, which lead to capillaries where nutrient and gas exchange occurs.
- Deoxygenated blood exits the tissues via venules, which merge into larger systemic veins.
- Systemic veins ultimately return deoxygenated blood to the right atrium.
Pulmonary Circulation
- The right side of the heart receives deoxygenated blood from the systemic circulation.
- Blood is ejected from the right ventricle into the pulmonary trunk, which branches into pulmonary arteries carrying blood to the lungs.
- Gas exchange occurs in pulmonary capillaries within the lungs.
- Oxygenated blood returns to the left atrium via pulmonary veins.
Coronary Circulation
- The coronary circulation delivers oxygenated blood and nutrients, and removes carbon dioxide and waste from the myocardium.
- The coronary arteries, branching from the ascending aorta, encircle the heart.
- Blood flow through the coronary arteries occurs during heart relaxation when high pressure from the aorta propels blood.
- Anastomoses (connections between arteries) provide alternative routes for blood flow if one artery becomes blocked.
- Blockage in a coronary artery can lead to myocardial ischemia and damage.
Coronary Arteries
- Two coronary arteries branch from the ascending aorta:
-
Left coronary artery:
- Circumflex branch: Supplies blood to the left atrium and left ventricle.
- Anterior interventricular artery: Supplies both ventricles.
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Right coronary artery:
- Marginal branch: Supplies blood to the right ventricle.
- Posterior interventricular artery: Supplies blood to both ventricles.
-
Left coronary artery:
Coronary Veins
- Deoxygenated blood from the coronary arteries flows through capillaries, collects waste and carbon dioxide, and then enters veins.
- Deoxygenated blood drains into the coronary sinus, a large vascular sinus located on the heart's posterior surface.
- The coronary sinus empties into the right atrium.
Myocardial Ischemia and Infarction
- Myocardial ischemia: Reduced blood flow through coronary arteries causes a lack of oxygen (hypoxia).
- Angina pectoris: Pain associated with myocardial ischemia.
- Myocardial infarction (heart attack): A complete blockage of a coronary artery causes heart muscle tissue death.
- Scar tissue replaces dead tissue.
Autorhythmic Fibers: The Conduction System
- Cardiac muscle cells are autorhythmic, generating spontaneous action potentials that trigger heart contractions.
- These cells act as a pacemaker, setting the rhythm for the entire heart.
- Autorhythmic cells form the conduction system, responsible for propagating action potentials (electrical impulses) throughout the heart muscle.
Conduction System of the Heart
- Components of the conduction system are:
-
Sinoatrial (SA) node:
- Located in the right atrium.
- Initiates heart activity by generating an action potential that spreads through both atria.
-
Atrioventricular (AV) node:
- Located in the interatrial septum.
- Delays the action potential to allow the atria to fully contract before ventricular contraction.
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Bundle of His:
- Carries the action potential from the AV node into the interventricular septum.
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Right and left bundle branches:
- Conduct the action potential down the interventricular septum to the apex of the heart.
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Purkinje fibers:
- Transmit action potentials from the bundle branches to the ventricular myocardium.
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Sinoatrial (SA) node:
Electrocardiogram (ECG)
- An electrocardiogram (ECG) records electrical activity in the heart.
- P wave: Represents atrial depolarization.
- QRS complex: Represents ventricular depolarization.
- T wave: Represents ventricular repolarization.
- QT interval: Represents the time from ventricular depolarization to ventricular repolarization.
The Cardiac Cycle
- One heartbeat is comprised of a single cardiac cycle.
- Systole: Contraction of the heart chambers.
- Diastole: Relaxation of the heart chambers.
- The phases of the cardiac cycle are:
- Atrial systole: Atria contract, forcing blood into ventricles.
- Ventricular systole: Ventricles contract, forcing blood into aorta and pulmonary trunk.
- Relaxation period: All chambers relax, allowing the heart to refill with blood.
Atrial Systole
- Lasts approximately 0.1 seconds.
- Atria contract while ventricles relax.
- The P wave on an ECG represents atrial depolarization, causing atrial systole.
- Atrial contraction pushes blood into the ventricles.
- By the end of atrial systole, each ventricle contains approximately 130 mL of blood (end-diastolic volume - EDV).
Ventricular Systole
- Lasts approximately 0.3 seconds.
- Ventricles contract while atria relax.
- The QRS complex on an ECG represents ventricular depolarization, causing ventricular systole.
- Ventricular contraction forces the AV valves to close.
- All valves are closed during this phase (isovolumetric contraction).
- Increasing ventricular pressure opens the semilunar valves, ejecting blood into the aorta and pulmonary trunk (ventricular ejection).
- The amount of blood ejected is the stroke volume.
Relaxation Period (Diastole)
- Lasts approximately 0.4 seconds.
- All chambers relax and refill with blood.
- The pressure in the ventricles falls below aortic and pulmonary trunk pressure, closing the semilunar valves.
- AV valves remain closed (isovolumetric relaxation).
- Ventricular pressure continues to decrease, allowing AV valves to open, initiating ventricular filling.
- Most blood passively flows into the ventricles during this phase.
Cardiac Output
- Cardiac output (CO) is the volume of blood ejected from the left ventricle each minute.
- Calculated by multiplying stroke volume (SV) by heart rate (HR): CO = SV x HR.
- Average CO at rest is 5 liters per minute.
Stroke Volume
- Stroke volume is the volume of blood ejected from the left ventricle each heartbeat.
- Determined by:
- Preload
- Contractility
- Afterload
Regulation of Stroke Volume
- Three factors regulate stroke volume:
- Preload: The degree of stretch on the heart prior to contraction.
- Contractility: The forcefulness of contraction of individual ventricular muscle fibers.
- Afterload: The pressure that must be exceeded before blood can be ejected from the ventricles.
Preload (Effect of Stretching)
- The Frank-Starling Law of the Heart: Greater preload (stretch) increases force of contraction.
- Preload is proportionate to end-diastolic volume (EDV).
- Two factors influence EDV:
- Duration of ventricular diastole: A shorter diastole leads to less filling time and smaller EDV.
- Venous return: Increased venous return results in more blood flowing into the ventricles, increasing EDV.
- The Frank-Starling Law helps equalize the output of the right and left ventricles, ensuring consistent blood flow to both the systemic and pulmonary circulations.
Contractility and Afterload
-
Contractility: Refers to the strength of contraction at a given preload.
- Positive inotropic agents: Increase contractility (e.g., sympathetic nervous system stimulation, epinephrine).
- Negative inotropic agents: Decrease contractility (e.g., calcium channel blockers).
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Afterload: The pressure that must be overcome by the ventricles to eject blood into the aorta and pulmonary trunk.
- Higher afterload reduces stroke volume.
Nervous System Control of the Heart
- The autonomic nervous system (ANS) regulates heart rate and contractility.
- Sympathetic division: Increases heart rate and contractility (fight-or-flight response).
- Parasympathetic division: Decreases heart rate (rest-and-digest response).
Factors Influencing Heart Rate
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Age, gender, physical fitness, and temperature influence heart rate.
- Higher heart rate in children than adults.
- Women tend to have higher heart rates than men.
- Fit individuals have lower heart rates than unfit counterparts.
- Heat increases heart rate, while cold decreases it.
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Description
This quiz covers key concepts regarding the cardiovascular system, focusing on the structure, orientation, and protection of the heart. Students will learn about the heart's composition, its positioning within the thoracic cavity, and the functions of the pericardium. It is essential for understanding how blood circulates throughout the body.
