B.46 Anatomy of the Heart Flashcards

Question

B. 46 Anatomy of the Heart Heart Sounds

Answer 1

S1 (lub): Closure of AV valves. S2 (dub): Closure of semilunar valves.

Answer 2

The mitral valve, also known as the left atrioventricular valve, is located in the left side of the heart and plays a crucial role in controlling blood flow between the left atrium and left ventricle. Location: The mitral valve is situated between the left atrium and the left ventricle. It is one of the four heart valves and is located posteriorly to the aortic valve and anterior to the left ventricle. Orientation: In terms of anatomical orientation, the mitral valve is positioned in a roughly vertical plane, with the atrial side facing posteriorly and the ventricular side facing anteriorly. The valve's annulus is tilted downwards towards the left ventricle. Support Structures Annulus Fibrosus: The mitral valve is anchored by the mitral annulus, a fibrous ring that provides structural support and maintains the shape of the valve orifice. This annulus secures the valve leaflets in place. Valve Leaflets:The mitral valve consists of two leaflets: the anterior leaflet and the posterior leaflet. Anterior Leaflet: Larger and more elongated than the posterior, it is more involved in the outflow tract to the left ventricle. Posterior Leaflet: Smaller and more triangular, it aids in closing the valve during ventricular contraction. Chordae Tendineae: These are fibrous cords that connect the valve leaflets to the papillary muscles in the left ventricle. They prevent the leaflets from prolapsing (flipping back into the left atrium) during ventricular contraction. Papillary Muscles: The papillary muscles are extensions of the heart muscle located within the left ventricle. They attach to the chordae tendineae and contract during ventricular systole, tightening the chordae to keep the mitral valve leaflets closed. Interventricular Septum: The muscular wall that separates the left ventricle from the right ventricle provides structural support to the mitral valve as it is located adjacent to this septal structure. Left Atrium:The mitral valve opens into the left ventricle from the left atrium, with the atrial wall serving as a boundary that interconnects with the valve annulus. Functional Importance The anatomical position and support structures of the mitral valve are crucial for its function during the cardiac cycle. During diastole, the valve allows blood flow from the left atrium to the left ventricle. During systole, the muscle contraction of the left ventricle closes the valve tightly to prevent regurgitation and ensure blood is pumped effectively into the aorta.

Answer 3

1. Left Anterior Descending Artery (LAD) * Pathway: The LAD runs in the anterior interventricular sulcus (groove) towards the apex of the heart. * Areas of Supply: * Anterior Wall of the Left Ventricle: Supplies a major portion of the anterior left ventricular wall. * Interventricular Septum: Provides blood to the anterior two-thirds of the interventricular septum. * Left Atrium: Supplies a portion of the left atrium. * Apex of the Heart: In some cases, the LAD reaches the apex, supplying that region as well. 2. Circumflex Artery (CX) * Pathway: The circumflex artery curves around the left side of the heart in the atrioventricular sulcus. * Areas of Supply: * Left Atrium: Supplies the majority of the left atrium. * Lateral Wall of the Left Ventricle: Provides blood to the lateral and posterior walls of the left ventricle. * Posterior Wall of the Left Ventricle: In many hearts, it supplies the inferior wall and part of the posterior wall of the left ventricle. * Atrioventricular Node: In some individuals, branches from the circumflex artery may supply the atrioventricular (AV) node. 3. Additional Branches of the LCA * Diagonal Branches: * These are smaller branches that arise from the LAD, typically ranging from one to several, and they supply specific areas of the anterior left ventricle. * Left Marginal Artery: * A branch of the circumflex artery, it supplies the lateral wall of the left ventricle. * Posterior Descending Artery (PDA): * In a "left dominant" coronary system, the PDA may arise from the circumflex artery, supplying the inferior wall of the left ventricle and the inferior part of the interventricular septum.

Answer 4

The left anterior descending artery (LAD) is the coronary artery most commonly occluded in myocardial infarctions (heart attacks), and it is often referred to as the "widowmaker". Reasons for Common Occlusion: 1. Area of Supply: * The LAD supplies a substantial portion of the heart, specifically the anterior wall of the left ventricle, the interventricular septum, and part of the apex. An occlusion in this artery can therefore affect a large area of the heart muscle that is critical for effective pumping. 2. High Demand: * The left ventricle is the chamber responsible for pumping oxygenated blood to the entire body, necessitating a significant blood supply. As a result, blockages in the LAD can lead to severe ischemia. 3. Type of Blockages: * A blockage in the LAD can lead to a large territory of muscle being deprived of oxygen, particularly the anterior wall and septum. This can result in a significant loss of function, potentially leading to heart failure or fatal arrhythmias. Why It’s Called the "Widowmaker": 1. Severity of Occlusion: * Occlusion of the LAD often leads to extensive myocardial damage due to the size of the area it supplies. This is particularly dangerous if the blockage is complete and not addressed quickly. 2. High Mortality Rate: * The term "widowmaker" reflects the high risk of sudden cardiac death associated with severe blockages in this artery, particularly because it can lead to fatal myocardial infarctions. Often affected individuals may die suddenly without prior warning signs, leaving their partners or family members in distress. 3. Association with Sudden Events: * Many people who experience an occlusion of the LAD may not exhibit classic symptoms of a heart attack until it is too late, leading to the perception that these events can strike unexpectedly.

Answer 5

The atrioventricular (AV) nodal delay holds significant importance in the electrical conduction system of the heart and plays a critical role in maintaining effective and coordinated heart contractions. Here are the main points regarding its significance: 1. Facilitates Atrial Contraction * Timing: The AV node provides a delay (about 40 milliseconds) in the conduction of electrical impulses from the atria to the ventricles. This delay allows the atria sufficient time to contract and completely empty their blood into the ventricles before the ventricles begin their contraction. 2. Prevents Rapid Ventricular Activation * Limiting Heart Rate: The AV node acts as a gatekeeper that places an upper limit on the heart rate; it ensures that impulses don’t continuously flood into the ventricles at excessively high frequencies. This is particularly important during times of increased autonomic stimulation or with certain arrhythmias, where maintaining a reasonable heart rate is vital for effective cardiac function. 3. Promotes Coordinated Contraction * Synchronized Functioning: By delaying the transmission of electrical impulses, the AV node ensures that the atrial contraction is completed before the ventricles contract. This coordination is essential for maximizing stroke volume, as it ensures that the ventricles are filled with blood from the atria prior to systole (ventricular contraction). 4. Protective Role in Arrhythmias * Preventing Excessive Atria Activity: The AV nodal delay helps protect the ventricles from excessively rapid atrial rates originating from the sinoatrial (SA) node or from ectopic foci. This is especially relevant in conditions like atrial fibrillation or atrial flutter, where the atria contract at very high rates. 5. Structural and Functional Integration * Transition Zone: The AV node serves as a transition zone between the atrial and ventricular types of myocardium. It is composed of transitional cardiac cells that possess unique conduction properties, allowing for slower conduction compared to the fast-conducting Purkinje fibers of the ventricular conduction system.

Answer 6

1. Role of Papillary Muscles * Anchor Points: The papillary muscles are attached to the inner walls of the ventricles and connect to the atrioventricular valves (the mitral and tricuspid valves) via the chordae tendineae. They provide an anchor for these cords. * Contraction During Systole: When the ventricles contract during systole, the papillary muscles also contract in coordination with the ventricular walls. This contraction pulls on the chordae tendineae, creating tension. * Preventing Leaflet Eversion: The tension generated by the papillary muscles through the chordae tendineae ensures that the valve leaflets are pulled down and held closed against their respective annuli (the fibrous ring where the valve leaflets attach). This action prevents the leaflets from being pushed back into the atria, thus stopping regurgitation of blood. 2. Role of Chordae Tendineae * Support for Valve Leaflets: The chordae tendineae are thin, fibrous cords that connect the papillary muscles to the edges of the valve leaflets. They act as supportive structures that transfer the force generated by the papillary muscles to the valve leaflets. * Tension Maintenance: As the ventricles contract, blood pressure rises, which tends to force the valve leaflets upward (or towards the atria). The tension in the chordae tendineae counteracts this upward force, effectively keeping the leaflets closed. * Preventing Eversion: By maintaining the proper configuration and tension, the chordae tendineae work to keep the leaflets together and prevent them from evaginating into the atrial cavity, thus maintaining unidirectional blood flow from the ventricles to the pulmonary artery (right ventricle) and aorta (left ventricle).