Study Guide - Chapter 19 - Heart PDF

Study Guide- Chapter 19- Heart Describe the general function of the cardiovascular system The general function of the cardiovascular system is to transport oxygen, nutrients, hormones, and waste products throughout the body. It consists of the heart, blood vessels, and blood. Differentiate among the...

Study Guide- Chapter 19- Heart Describe the general function of the cardiovascular system The general function of the cardiovascular system is to transport oxygen, nutrients, hormones, and waste products throughout the body. It consists of the heart, blood vessels, and blood. Differentiate among the three primary types of blood vessels. Arteries carry oxygenated blood away from the heart, veins transport deoxygenated blood back towards the heart, and capillaries facilitate exchange of substances between the bloodstream and surrounding tissues. Describe the general structure and function of the heart. Structure: - Size and shape: Approximately the size of a closed fist, cone-shaped. - Location: Located in the chest cavity, between the lungs, slightly to the left side. - Layers: Consists of three layers - epicardium (outermost layer), myocardium (middle layer composed of cardiac muscle), and endocardium (inner lining). Function: - Pumping action: Contracts and relaxes rhythmically to pump blood throughout the circulatory system. - Circulation: Receives deoxygenated blood from the body via veins and pumps oxygenated blood out to various organs and tissues via arteries. - Valves: Contains four valves - tricuspid valve, pulmonary valve, mitral valve, and aortic valve - that ensure unidirectional flow of blood through the heart chambers. - Electrical impulses: Generates electrical signals that regulate the heartbeat, ensuring coordinated contractions. Compare and contrast pulmonary circulation and systemic circulation of the cardiovascular system. Trace blood flow through both circulations. 1. "Pulmonary circulation focuses on oxygenating blood in order to remove carbon dioxide from it, whereas systemic circulation delivers oxygen-rich blood throughout our entire body." 2. The flow of pulmonary circulation goes from right ventricle → pulmonary artery → alveolar capillaries → pulmonary veins → left atrium. 3. The flow of systemic circulation starts at left atrium → left ventricle → aorta → arteries → arterioles → capillaries → venules → veins → right atrium. Describe the location and position of the heart in the thoracic cavity. The heart is centrally located within the thoracic cavity, in a region known as the mediastinum. It is slightly inclined towards the left side of the chest and occupies an oblique position between the second rib and fifth intercostal space. List the structural components of the pericardium. 1. Fibrous Pericardium: The fibrous pericardium is the tough, outermost layer of the pericardial sac. 2. Serous Pericardium: The serous pericardium consists of two layers - the parietal layer and the visceral layer. 3. Parietal Layer: The parietal layer lines the inner surface of the fibrous pericardium and forms the outer wall of the pericardial cavity. 4. Visceral Layer (Epicardium): The visceral layer, also known as epicardium, covers the heart's surface directly. 5. Pericardial Cavity: The space between the parietal and visceral layers is called the pericardial cavity, which contains a small amount of fluid to reduce friction during heart contractions. 6. Pericardial Fluid: Pericardial fluid is a lubricating fluid found within the pericardial cavity that helps reduce friction between the layers of the pericardium during cardiac movements. Describe the function of the pericardium and the purpose of the serous fluid within the pericardial cavity. The pericardium serves to protect and stabilize" the heart, while "serous fluid reduces friction" between its layers. Compare the superficial features of the anterior and posterior aspects of the heart. Anterior Aspect of the Heart: - Location: The anterior aspect of the heart is located towards the front of the chest, behind the sternum (breastbone). - Surface features: It includes the right atrium and right ventricle, which form the majority of the visible anterior surface of the heart. - Structures: The superior vena cava and inferior vena cava enter into the right atrium, while the pulmonary trunk exits from the right ventricle. - Coronary vessels: The right coronary artery can be seen running along the anterior surface, supplying blood to both ventricles. Posterior Aspect of the Heart: - Location: The posterior aspect of the heart is situated towards the back of the chest cavity. - Surface features: It consists mainly of the left atrium and left ventricle, which are visible from a posterior view. - Structures: The four pulmonary veins enter into the left atrium, while the aorta exits from the left ventricle. - Coronary vessels: The left coronary artery is found on this side, supplying blood to both ventricles. Name the three layers of the heart wall and the tissue components of each. Layer 1: Epicardium - Tissue component: Thin layer of connective tissue and epithelial cells - Function: Provides a protective outer covering to the heart Layer 2: Myocardium - Tissue component: Thick layer of cardiac muscle cells - Function: Responsible for contracting and pumping blood throughout the body Layer 3: Endocardium - Tissue component: Inner lining made up of endothelial cells - Function: Forms a smooth surface for efficient blood flow within the heart chambers Characterize the four chambers of the heart and their functions. Chamber: Right Atrium Function: Receives deoxygenated blood from the body and pumps it to the right ventricle. Chamber: Right Ventricle Function: Receives deoxygenated blood from the right atrium and pumps it to the lungs for oxygenation. Chamber: Left Atrium Function: Receives oxygenated blood from the lungs and pumps it to the left ventricle. Chamber: Left Ventricle Function: Receives oxygenated blood from the left atrium and pumps it to the rest of the body. Compare and contrast the structure and function of the two types of heart valves. Type of Heart Valve: Aortic Valve Structure: - The aortic valve is a tricuspid valve with three leaflets, also known as cusps or flaps. - It consists of fibrous tissue covered by thin layers of endothelial cells. - The leaflets are attached to the annulus, a ring-shaped structure that surrounds the opening of the aorta. Function: - The main function of the aortic valve is to prevent the backflow of blood from the aorta into the left ventricle. - When the left ventricle contracts, it forces blood through the aortic valve and into the systemic circulation. - After systole (contraction phase), when the ventricles relax, the aortic valve closes to prevent blood from flowing back into the heart. Type of Heart Valve: Mitral Valve Structure: - The mitral valve, also known as bicuspid valve, has two leaflets or cusps. - Similar to other heart valves, it consists of fibrous tissue covered by thin layers of endothelial cells. - The leaflets are attached to papillary muscles in the left ventricle via chordae tendineae, which provide support and stability. Function: - The primary function of the mitral valve is to regulate blood flow between the left atrium and left ventricle. - During diastole (relaxation phase), when blood fills up in the left atrium, it passes through an open mitral valve into the left ventricle. - As systole begins (contraction phase), the mitral valve closes tightly to prevent any backflow into the atrium. Describe the location and function of the fibrous skeleton. Location: The fibrous skeleton is located within the heart, specifically in the middle layer known as the myocardium. It surrounds and supports the four chambers of the heart. Function: The fibrous skeleton serves several important functions in the heart: 1. Structural Support: It provides a sturdy framework for the attachment of cardiac muscle fibers, ensuring proper alignment and coordinated contraction of the heart chambers. 2. Electrical Insulation: The fibrous skeleton acts as an electrical insulator between different regions of the heart. This prevents abnormal electrical impulses from spreading to unwanted areas, thus maintaining a synchronized and efficient heartbeat. 3. Valve Support: It provides support for the heart valves by forming dense connective tissue rings around them. These rings help maintain the shape and integrity of the valves, preventing their prolapse or collapse during blood flow. 4. Separation of Atria and Ventricles: The fibrous skeleton forms a barrier between the atria (upper chambers) and ventricles (lower chambers) of the heart. This separation helps channel blood flow in a specific direction, allowing efficient filling and ejection of blood during each cardiac cycle. Describe the general structure of cardiac muscle. Intercalated Discs: Specialized junctions between adjacent cardiac muscle cells that allow for rapid transmission of electrical signals. They contain desmosomes to provide mechanical strength and gap junctions to facilitate electrical coupling. Branched Fibers: Cardiac muscle fibers are interconnected, forming a network that allows for coordinated contraction. This branching pattern enables efficient distribution of electrical impulses throughout the heart. Striations: Cardiac muscle exhibits a striped appearance under a microscope due to the presence of organized sarcomeres. These repeating units consist of thick myosin filaments and thin actin filaments responsible for muscle contraction. Explain the intercellular structures of cardiac muscle 1. Intercalated Discs: "Intercalated discs are specialized cell-to-cell junctions that connect adjacent cardiac muscle cells." These disc-like structures contain three main components - desmosomes, gap junctions, and fascia adherens. 2. Desmosomes: "Desmosomes provide strong mechanical adhesion between neighboring cardiac muscle cells." They consist of transmembrane proteins called cadherins, which link with the intermediate filaments of adjacent cells, providing structural stability to the tissue. 3. Gap Junctions: "Gap junctions allow for electrical coupling between cardiac muscle cells." These small channels formed by connexin proteins permit the passage of ions and small molecules, facilitating rapid transmission of action potentials and synchronization of contractions throughout the myocardium. 4. Fascia Adherens: "Fascia adherens form a continuous belt-like structure along the intercalated discs." They anchor actin filaments to the plasma membrane, promoting structural integrity and transmitting contractile forces during muscle contraction. Discuss how cardiac muscle meets its energy needs. - Cardiac muscle primarily relies on aerobic metabolism to meet its energy demands. - The main source of energy for cardiac muscle is adenosine triphosphate (ATP). - ATP is produced through the process of oxidative phosphorylation in the mitochondria of cardiac muscle cells. Identify the coronary arteries, and describe the specific areas of the heart supplied by their major branches. 1. Left Main Coronary Artery (LMCA):The left main coronary artery is an important branch of the ascending aorta that supplies oxygenated blood to the left side of the heart. 2. Left Anterior Descending Artery (LAD): "The LAD is a major branch of the left main coronary artery and supplies blood to the anterior wall of the left ventricle, interventricular septum, and apex of the heart." 3. Circumflex Artery (Cx): "The circumflex artery originates from the left main coronary artery and supplies blood to the lateral wall of the left ventricle." 4. Right Coronary Artery (RCA): "The right coronary artery arises from the right sinus of Valsalva and provides blood supply to most of the right atrium, right ventricle, inferior wall of the left ventricle, and part of the interventricular septum." 5. Posterior Descending Artery (PDA): "The PDA is a branch of either the RCA or Cx artery, depending on anatomical variation, and supplies blood to the posterior walls of both ventricles and part of the interventricular septum." Explain the significance of coronary arteries as functional end arteries. The left and right coronary arteries are considered functional end arteries because, although there coronary arteries have anastomoses, if one of the arteries becomes blocked these anastomoses are too tiny to shunt sufficient blood from one artery to the other. As a result, the part of the heart wall that was supplied by one coronary artery branch will die due to lack of blood flow to the tissue. Describe blood flow through the coronary arteries. Blood flow to the heart wall is not a steady stream; it is impeded and then flows, as the heart rhythmically contracts and relaxes. Identify the coronary veins, and describe the specific areas of the heart drained by their major branches. 1. Great Cardiac Vein: The great cardiac vein drains the left atrium, left ventricle, and interventricular septum. 2. Middle Cardiac Vein: The middle cardiac vein drains the posterior surface of the left ventricle. 3. Small Cardiac Vein: The small cardiac vein drains the right atrium and right ventricle. 4. Anterior Cardiac Veins:The anterior cardiac veins drain the right ventricle and open directly into the right atrium. 5. Coronary Sinus: The coronary sinus is a large venous channel that receives blood from most of the coronary veins and empties into the right atrium. Identify and locate the components of the heart’s conduction system. 1. SA Node (Sinoatrial Node): - Located in the right atrium near the superior vena cava. -The SA node is often referred to as the natural pacemaker of the heart. 2. AV Node (Atrioventricular Node): - Located in the lower portion of the right atrium, near the septum. - The AV node acts as a relay station between the atria and ventricles, delaying electrical impulses before transmitting them to ensure proper coordination 3. Bundle of His: - Located in the upper part of the interventricular septum. - The bundle of His divides into left and right branches, which carry electrical signals down each side of the septum towards the ventricles. 4. Purkinje Fibers: - Located throughout both ventricles, branching from the bundle branches. - "Purkinje fibers distribute electrical impulses rapidly through specialized muscle cells, allowing coordinated contraction of both ventricles. Compare and contrast parasympathetic and sympathetic innervation of the heart. Parasympathetic innervation of the heart: - Originates from the vagus nerve (cranial nerve X). - Releases acetylcholine as its primary neurotransmitter. - Acts to slow down heart rate and decrease cardiac output. - Stimulates the release of nitric oxide, which causes vasodilation in coronary blood vessels. - Mediates a "rest and digest" response. Sympathetic innervation of the heart: - Originates from preganglionic neurons in the thoracic region of the spinal cord (T1-T4) and releases norepinephrine as its primary neurotransmitter. - Activates the fight or flight response. - Increases heart rate, contractility, and cardiac output. - Causes vasoconstriction in peripheral blood vessels but promotes vasodilation in coronary blood vessels to increase myocardial oxygen supply. Describe a nodal cell at rest At rest, nodal cells have a stable membrane potential called the resting membrane potential. Resting Membrane Potential: - The resting membrane potential of a nodal cell is approximately -60 mV to -70 mV. - This negative charge inside the cell is maintained by a higher concentration of negatively charged ions, such as proteins and organic anions, compared to outside the cell. - It is primarily regulated by potassium (K+) ion channels that allow K+ to flow out of the cell, contributing to its negativity. - The resting membrane potential allows nodal cells to remain electrically stable until stimulated. - It provides a baseline for depolarization, which triggers action potentials necessary for generating electrical signals within the heart. - A stable resting membrane potential ensures regular rhythmic contractions and proper coordination between different parts of the heart. Define autorhythmicity. Autorhythmicity refers to the inherent ability of certain cells or tissues in the body to generate spontaneous electrical impulses at regular intervals without any external stimulation. These cells are capable of initiating and conducting these electrical signals, which play a crucial role in regulating various physiological processes, such as heart rate and contraction. Describe the steps for SA nodal cells to spontaneously depolarize and serve as the pacemaker cells. 1. Reaching threshold as Na+ enters the nodal cells through open voltage-gated Na+ channels 2. depolarization as Ca2+ enters the nodal cells through open voltage-gated Ca2+ channels 3. Repolarization as K+ exits the nodal cells through voltage-gated K+ channels Describe the spread of the action potential through the heart’s conduction system. The action potential originates in the sinoatrial (SA) node, also known as the natural pacemaker of the heart. "The SA node generates an action potential that spreads across both atria, causing them to contract simultaneously." - From the SA node, the action potential travels through specialized conduction pathways called internodal pathways towards the atrioventricular (AV) node. "Internodal pathways conduct the electrical impulse from the SA node to the AV node, facilitating coordinated contraction between the atria and ventricles." - At the AV node, there is a slight delay in order to allow for complete atrial contraction before ventricular contraction begins. "The AV node delays conduction for about 0.1 seconds, allowing time for atrial contraction and filling of blood into ventricles." - After passing through the AV node, the action potential enters into the Bundle of His or atrioventricular bundle. "The Bundle of His fibers rapidly transmit electrical signals from the AV node to the Purkinje fibers." - The Purkinje fibers then distribute the action potential throughout both ventricles, causing them to contract simultaneously. "The fast-conducting Purkinje fibers rapidly spread excitation throughout all regions of both ventricles, resulting in synchronized ventricular contraction." Describe the conditions at the sarcolemma of cardiac muscle cells at rest. 1. RMP is -90 mV. 2. Contains fast voltage-gated Na+ channels for depolarization and K+ voltage-gated channels for repolarization of membrane. 3. Also contains slow voltage-gated Ca+ channels List the electrical events of an action potential that occur at the sarcolemma. 1. Depolarization: An action potential triggers the opening of fast voltage-gated Na+ channels in the sarcolemma. The resulting resting membrane potential changes from -90 mV to +30 mV. Voltage-gated Na+ channels close to inactivated state. 2. Plateau: Depolarization triggers the opening of voltage-gated K+ channels and K+ leave the cardiac muscle cells. Slow voltage-gated Ca+ channels open and Ca+ enters the cell. The exit of K+ and simultaneous entrance of Ca+ results in no electrical change, and the sarcolemma remains in a depolarized state. 3. Repolarization: Voltage-gated Ca+ channels then close and K+ channels remain open to complete repolarization as K+ exits the cells. Membrane potential of -90 mV is then reestablished. Briefly summarize the mechanical events of muscle contraction. The entry of Ca+ into the sarcoplasm from the plateau allows Ca+ to bind to troponin and begin cross-bridge cycling within a sarcomere, similar to skeletal muscle contraction. The closing of voltage-gates Ca+ channels, reuptake of Ca+ into the sarcoplasmic reticulum by Ca+ pumps, and removal of Ca+ from the cell by plasma membrane Ca+ pumps decrease Ca+ levels in the sarcoplasm. Calcium is released from troponin with subsequent decrease in cross-bridges between thin and thick filaments. Sarcomeres return to their original resting length. Define the refractory period. Refractory period is the period of time following an action potential during which a neuron or muscle fiber cannot generate another action potential. It is characterized by a temporary state of reduced excitability, preventing the neuron from being immediately stimulated again. Explain the significance of the plateau phase The plateau phase delays repolarization and allows the sarcomeres of cardiac muscle cells to fully contract and relax before following each stimulation. This prevents cardiac muscle cells from exhibiting tetany which would result in the locking up of heart chambers. Identify the components of the ECG recording components of an ECG recording consist of electrodes, leads, an ECG machine, a paper strip, calibration markers, waves and intervals, measurements, and interpretation software Waves 1. P wave: Reflects atrial depolarization that originates in the SA node. Typically lasts 0.008 to 0.1 seconds. 2. QRS complex: Represents ventricular depolarization 3. T wave: Represents ventricular repolarization. Segments P-Q segment: Associated with atrial plateau when the cardiac muscle cells within the atria are contracting. S-T segment: The ventricular plateau when cardiac muscle cells within the ventricles are contracting. Intervals P-R interval: represents the period of time between the beginning of the P wave to the beginning of the QRS deflection. Q-T interval: time from the beginning of the QRS complex to the end of the T wave. Identify the two processes within the heart that occur due to pressure changes associated with the cardiac cycle. 1. Ventricular Contraction (Systole): "During ventricular contraction, or systole, the pressure within the ventricles increases, causing the blood to be forcefully ejected into the pulmonary artery and aorta. 2. Ventricular Relaxation (Diastole): "During ventricular relaxation, or diastole, the pressure within the ventricles decreases, allowing blood to flow back into the relaxed chambers from the atria. List and describe what occurs during the five phases of the cardiac cycle. 1. Atrial systole is the contraction of atria to finish filling the ventricles, which are in diastole. 2. Early ventricular systole is a time of isovolumetric contraction: Ventricles begin to contract, AV valves are pushed closed, and no blood leaves the ventricles yet. 3. Late ventricular systole is the time of ventricular ejection: Semilunar valves are pushed open, and blood is forced through the semilunar valves into the arterial trunk. 4. Early ventricular diastole is the beginning of ventricular relaxation: AV valves remain closed, and semilunar valves close. 5. Late ventricular diastole is a time to begin ventricular filling as AV valves open and passive filling of the ventricle begins. Explain the significance of ventricular balance. The term "ventricular balance" refers to the equal distribution of blood flow between the left and right ventricles of the heart. Significance: 1. Efficient Pumping: Ventricular balance ensures that both sides of the heart work together effectively, allowing for optimal pumping of oxygenated blood to the body and deoxygenated blood to the lungs. 2. Normal Functioning: Maintaining ventricular balance is crucial for maintaining normal cardiac function and preventing conditions such as congestive heart failure, where an imbalance in ventricular workload can lead to inadequate pumping and fluid accumulation. 3. Hemodynamic Stability: By achieving ventricular balance, the heart can maintain a stable hemodynamic state, ensuring adequate perfusion to vital organs and tissues throughout the body. Define cardiac output. Cardiac output represents the efficiency and effectiveness of the heart's pumping action. It is calculated by multiplying the stroke volume (the amount of blood ejected with each heartbeat) by the heart rate (the number of times the heart beats per minute). Cardiac output provides a measure of how well the heart is able to deliver oxygenated blood to tissues throughout the body. A healthy adult at rest typically has a cardiac output between 4-8 liters per minute, which can increase during exercise or in response to certain physiological conditions or diseases Explain what is meant by cardiac reserve. Cardiac reserve refers to the ability of the heart to increase its output in response to increased demand, such as during physical exertion or stress. It represents the difference between a person's resting cardiac output and their maximum achievable cardiac output. Define chronotropic agents, and describe how they affect heart rate. External variables that operate on the SA node (the pacemaker) and the AV node may change the heart rate. Autonomic nervous system innervation and fluctuating hormone levels are the key extrinsic variables that raise and decrease heart rate. These variables that affect heart rate are chronotropic agents, and they may be classed as either positive or negative chronotropic agents. - Positive chronotropic agents - increase heart rate. - Negative chronotropic agents - decrease heart rate. Discuss how autonomic reflexes alter heart rate. Cardiac center receives sensory input from baroreceptors and chemoreceptors. Cardiac center responds by altering nerve signals that innervate the heart to maintain homeostasis List the three variables that may influence stroke volume. 1. Preload: Preload refers to the degree of stretch on the ventricular muscle fibers just before contraction and is determined by the volume of blood returning to the heart from the venous system. 2. Afterload: Afterload is defined as the force against which the heart must work to eject blood during systole and is influenced primarily by systemic vascular resistance. 3. Contractility: Contractility refers to the inherent ability of cardiac muscle fibers to shorten actively and develop force. Summarize the variables that influence cardiac output Various circumstances influence heart rate, stroke volume, and cardiac output: ● Heart rate - The conduction system is influenced by chronotropic drugs, which cause a rise or decrease in heart rate. The SA node is stimulated to modify its firing rate, while the AV node is stimulated to adjust the degree of delay. Explain how postnatal heart structures develop from the primitive heart tube. The heart develops during the third week of pregnancy when the embryo is too big to obtain nutrients only by diffusion. By day 19, the embryo has formed two heart tubes from the mesoderm. These paired tubes unite on day 21, creating a single primitive heart tube. On day 22 the heart starts to beat, and by the fourth week, this single heart tube has bent and folded in on itself to produce the exterior heart shape. This tube makes expansions, resulting in postnatal cardiac structures: ● sinus venosus ● primitive atrium ● primitive ventricle ● bulbus cordis The five regions of the primitive heart tube develop into recognizable structures in a fully developed heart. The truncus arteriosus will eventually divide and give rise to the ascending aorta and pulmonary trunk. The bulbus cordis develops into the right ventricle. The primitive ventricle forms the left ventricle. Describe septal defects that may occur during development. The postnatal heart with an atrial septal defect retains an opening between the left and right atria. Thus, blood is diverted from the left atrium to the right atrium. This may result in right-sided heart hypertrophy. Ventricular septal defects may emerge due to an incompletely constructed interventricular septum. Tetralogy of Fallot is a frequent abnormality that arises when the aorticopulmonary septum divides the truncus arteriosus unevenly. Consequently, the patient has a ventricular septal defect, a very thin pulmonary trunk, an aorta that crosses both the left and right ventricles, and right ventricle hypertrophy.