Heart Valve Anatomy PDF

Heart valve anatomy • 4 valves in total • 2 semilunar valve and 2 atrioventricular valve (AV valve) • Function: enables unidirectional flow of blood in blood vascular system. Atrioventricular valve (AV valve) • Function - prevent blood returning to atria during ventricular contraction • Right AV val...

Heart valve anatomy • 4 valves in total • 2 semilunar valve and 2 atrioventricular valve (AV valve) • Function: enables unidirectional flow of blood in blood vascular system. Atrioventricular valve (AV valve) • Function - prevent blood returning to atria during ventricular contraction • Right AV valve - tricuspid valve • Left AV valve - bicuspid (mitral) valve • • Diastole - filling phase, AV valves open and blood flows from atria into ventricles (Ventricular) Systole - contractile phase, AV valves are "pushed" shut by the raised pressure in the ventricle; once sufficient pressure accumulates in the ventricles, semi-lunar valves are pushed open Semilunar valve • Function - prevent blood returning to ventricles during filling (diastole) • Right SL valve - pulmonary (semilunar) valve, 3 cusps --> pulmonary circuit • Left SL valve - aortic (semilunar) valve, 3 cusps --> systemic circuit • • (Ventricular) Systole - pushed open as blood flows out of heart when pressure in the ventricle becomes sufficient to overcome the residual pressure of the artery Diastole - closes as blood backflows when pressure in the ventricle decreases relative to the pressurised artery Papillary muscles - one of the first part of the ventricle to contract during systole; tenses pretension cables to hold the cusps and control the closing of the valves when the pressure increases in ventricles Chordae tendineae - strong tendinous strands o Diastole - CT loose; AV valves offer no resistance to the flow of blood from atria into ventricles (AV valves open) o Systole - CT tense; ventricles and papillary muscles contract, preventing the cusps before swinging into the atria; blood moving towards atria pushes cusps of AV valve together, closing them and preventing backflow Cardiac muscle (myocardium) • Display features of both smooth and skeletal muscle as well as cardiac muscle specialisations • Function: beating and contracting of the heart • Location: exclusive to the heart o Organised myofibrils and aligned sarcomeres give the cells a striated appearance o Short, branched cells o Irregular branched sarcomere - sarcomeres arranged at different angles (sarcomeres bend into different branches) o 1 (occasionally 2) central nuclei per cell o Central nucleus that is oval shaped o Cytoplasmic organelles packed at the poles of nucleus o Interconnected with neighbouring cells via intercalated disks (ICDs) o Highly vascular o Mitochondria 20% of volume of cell - cells heavily rely on oxygen dependent aerobic metabolism to obtain the energy required for continuous contraction Intercalated disks (ICDs) – 3 types: adhesion belts, desmosomes, gap junction • • • Adhesion belts or fascia adherens (vertical portion) - linking actin to actin so that contraction of actin from one cardiomyocyte become transmitted to the next (physical propagation of contraction) Desmosomes - linking cytokeratin with cytokeratin; anchoring junctions between membranes of adjacent cardiomyocytes during contraction Gap junction (horizontal portion, parallel to plane of contraction) - electrochemical communication via cytoplasmic contact; electrochemical propagation of contraction Conduction system of the heart • The actions of the conduction system greatly increase the efficiency of the heart pumping. • The system is responsible for the co-ordination of heart contraction and especially atrioventricular valve action (ensuring papillary muscles are contracted before systole) • Autonomic nerves/tone alter the rate of conduction impulse generation o Innervated by sympathetic and parasympathetic pathways o Parasympathetic tone increases when relaxed - heart beats slower o Sympathetic tone increases when excited - heart beats faster • Conduction pathways are NOT nervous tissue but modified cardiomyocyte Conduction cells vs. Contractile cardiac muscle cells (cardiomyocytes) • Conduction cells - bloated, non-contractile cardiac muscles involved with electrical conduction o Some peripheral myofibrils o Central nucleus o Many mitochondria and large store of glycogen - conduction role very energy dependent o Lots of gap junctions - intercalated disks dominated by gap junctions (mainly electrochemical communication) o Some desmosomes and few adhesion belts o 1% of cardiac cells Vessels of the cardiac circulation • Cardiac circulation is enabled by the myocardium present in the atria and ventricles (mostly ventricles because ventricular walls contain more myocardium). • Oxygenated blood is directly supplied to the myocardium from the ascending aorta via the left and right coronary arteries o Right coronary artery - starting from the base of the ascending aorta, runs along the groove between R atrium and ventricle in the epicardium, over the anterior surface of heart, extending to posterior of heart and branching into smaller branches that enter the myocardium (supplies right atrium and ventricle) o Left coronary artery - starting from the base of the ascending aorta, short stem branch into (1) anterior surface of heart AND (2) groove between left atrium and left ventricle ▪ (1) runs over intraventricular septum - anterior interventricular artery ▪ (2) runs around to the posterior and circumflexes around left lateral margin and meets and fuses with small branches of the right coronary artery circumflex artery • • • Small cardiac vein drain areas supplied by the right coronary artery (right atrium and ventricle) Great cardiac vein drain areas that were supplied by anterior interventricular artery and circumflex artery Both small cardiac vein and great cardiac vein drains deoxygenated blood into the coronary sinus, an expanded vein that opens into the right atrium