Physiology of the Heart

Physiology of the HeartAnatomy1. Illustrate and pick out the gross anatomy of the cheek. Include the layers of the snapper wall, domiciliate, valves, coordinates and major kindred vessels machine-accessible to the cheek. Indicate direction of flow. Include your own plat.The touchwood is a mazy biological electric pump. It is found in mediastinum of the thorax. Surrounding the burden is the pericardium, which contains serous fluid, allowing the cheek to move freely within the tissue layer. (1) The outside surface of the center is known as the epicardium, the inner surface of the heart muscle-builder the myocardium and the inmost surface the endocardium.The heart itself potbelly be uninvolved into 4 chambers which be filled with rootage when the heart is relaxed, and pumped out of when the heart contracts. (1) They argon separated into the left and overcompensate side, which be unadorned, and into atria (singular atrium) and ventricles. The atria and ventricles ar e separated by the coronary sinus or AV groove. amidst the right atrium and right ventricle is the Tricuspid Valve which is make up of 3 leaflets. Deoxygenated argument contri andes into the right atrium from the Vena Cava (which is separated into the weapons-grade and inferior vena cava superior from the head, neck and arms and the inferior from the lower limbs and the abdomen). (1) The right ventricle feeds into the pulmonic artery which carries deoxygenated pedigree to the lungs. Blood is then oxygenated and fed back to the heart through with(predicate) with(predicate) the pulmonary vein. This fills the left atrium and subsequently, flows through the Mitral Valve into the left ventricle.. (1) As the heart contracts, this pushes the blood into the aorta, which feeds through to the major arteries in the body. Within the paper of the aorta lies some in truth small arteries known as the coronary arteries. These feed the heart tissue with oxygenated blood and drain into the right atrium, with the organisationic deoxygenated blood. (1)2. presently describe the function of the pericardial cavityAs mentioned before, the heart and grow of the great vessels (aorta, vena cava, pulmonary vein and artery) is surrounded with a very strong membrane known as the pericardium. It is a double walled structure, made up of the fibrous pericardium on the outermost surface of the heart, and an inner serous pericardium. (1)The fibrous pericardium is made of very dense connective tissue, and contains many another(prenominal) collagen fibres. It pr levelts overfilling of the heart and anchors it to the surrounding walls of the thoracic cavity.(2) The serous pericardium gutter be differentiated into dickens layers, the parietal layer, which is fused and continuous with the fibrous pericardium, and the visceral pericardium which can similarly be known as the epicardium. Between these layers is a potence aloofness known as the pericardial cavity, filled with roughly 50mls of serous fluid. (2) This potential space is extremely important as it allows the heart to move freely within the space by keeping the transmural cardiac pressures very low, as well as facilitating atrial filling during ventricular systole by maintaining a negative pericardial pressure. It also stops hypertrophy of the heart under energetic exercise, keeping the heart muscle a relatively constant size. (2) The membranes altogether isolate the heart from the thoracic cavity which prevents pass on of disease or infection. Its importance is particularly obvious when there are cases of pericardial tamponade build-up of fluid in the pericardial cavity which causes compression of the heart. (2) Without the pericardial cavity, the heart would not be adequate to pump as efficiently as it would moderate to overcome the pressures exerted on it by the surroundings, which would just add to the mould of the cardiac muscle.(2)3. Illustrate and describe the anatomy of the electric al conduction placement of the heart. Briefly describe the blood supply to the electrical conduction system.The electrical impetus originates at the Sino Atrial leaf node in the right atrium. This disposition travels through the cardiac muscle through the many gap junctions, as well as through the intermodal pathways or Bachmans bundle. (1) At the take of the atrio-ventricular valves, there is other node called the Atrio-ventricular client (AV Node) that has properties that delay the stimulus. Following this, the impulse travels set down the left and right bundle setoff fibres in the ventricular septum, into the bundles of His which travel up the ventricular walls and branch into Purkinje fibres. The stimulus reaches the apex of the heart first, and then travels up towards the outflow tracts resulting in coordinated depolarisation and contr perform. (1) This coordination is a result of two the coordination of the stimulus as well as the layout of the myocytes, as well as the ease at which the electrical channelize is able to propagate through cardiac muscle.(3) Sino Atrial Node is ordinarily supplied oxygenated blood by the Right coronary thrombosis arterial blood vessel (RCA) or the leftfield Coronary Artery (LCA) though this is variable. In most people, the AV Node is supplied by the AV Node Artery branch of the Posterior Descending Artery which is a branch off the RCA, though in some it impart be supplied by the same artery, just as a branch of the left Circumflex Artery. (3) All of the fibres downstream from this point are supplied by the Left Anterior Descending artery with exception of the His fibres, which are also supplied by the AV Node Artery. (3)Conduction1. Illustrate and describe the propagation of a single beat through the electrical conduction system and the relationship to the surface cardiogram. Include in your answer a discussion on conduction velocity through the various components and list the pattern ECG intervals.An ECG w orks by detecting the electrical change in the heart through sensors that are put on the surface of the skin. caution is determined through the use of electrical vectors generated by many hundreds of single booths. (4)The P cockle is the first small shiver in the ECG. It reflects the deal out of depolarisation through the atria from the SA node. The normal range is 0.08-0.1seconds. After the P wave there is a brief isoelectric stage when the current is flowing through the AV node, and the conduction is easilyed. This is known as the PR interval and it is commonly 0.12-0.2seconds. (4) The QRS complex shows the very strong electrical signal and resulting abridgment that forces blood into the aorta and pulmonary artery. It is about 0.06-1seconds, which shows just how fast depolarisation spreads through the ventricles (its abidance has been idealised on the schematic below). (1) After the QRS complex there is another isoelectric achievement which indicates plateau phase of de polarisation. The T wave is the repolarisation of the ventricles in readiness for the next beat the duration between the P and T waves usually approximately 0.2-0.4seconds, though this is dependent on heart rate.(4) The U wave is a very rarely seen artefact and is thought to reflect the repolarisation of the papillose muscles that control the valves. (1)Figure 3 Electrocardiogram schematic. Based on the diagram from Bruce Shade fast(a) and Easy ECGs (4)2. Briefly describe the ionic private road that occurs during each phase of the myocardial and SA node action potential. Include a labelled illustration of both action potentials in your answer.The myocardial action potential is quite complex with influxes and effluxes of 3 different ions, changing the membrane potential as contraction occurs. There are 5 distinct phases of the myocardial action potential. (1) These are shown in the figure 4 below. Between phase 0 and 2 there is an absolute refractory period where it is impossibl e to invoke another action potential. This allows even to a greater extent coordination of the spread of a stimulus.(1) The ECG trace shown below the action potential shows where the stages of contraction occur that can be extrapolated out into the ventricular depolarisation (QRS complex) and the ventricular repolarisation (T wave)Depolarisation RepolarisationECGCells in the SA node are pacemaker cells and have a berth which is known as automaticity. They do not take away activation to fire an action potential.(1) They are very similar to myocytes but have several key differences in their action potentials (see figure 5). material body 0 is significantly slowlyer in the pacemaker cells of the SA node as it is dependent on the activation of L-type calcium channels instead of sodium channels, which makes the depolarisation significantly slower at this phase.(1) During Phase 1, repolarisation of the membrane occurs leading to a period of pacemaker potential, where the membrane pot ential gradually depolarises through constant Na2+ leakage into the cell. When the action potential is triggered automatically, Phase 0 commences. artificial pacemaker cells do not have phase 1 and 2. (1)Figure 5 SA Node Action Potential 3. Describe the procedure of escape pacemakers in the conduction system.The SA node is entirely autonomous which means that it does not impoverishment external innervation or activation to fire. Other areas of the heart are heteronomous which means they need an external source of action potential to sire them to produce one. (1) Some specific cells along the conduction fibres possess both of these properties. This is so that if the SA Node fails for some reason, they can activate themselves and this allows the heart to beat, even without a functional SA Node. (1) Each area will have a slower rate of autonomy as it gets further downstream from the SA Node to prevent competition between the different areas. (5) This is very useful when the SA Node fails, and the AV Node takes over as the AV Node can maintain a BPM of about 40-60 BPM which is still slow but can maintain life for a reasonable bar of time. Further downstream the Bundles of His can maintain about 25-40 BPM and the Purkinje fibers about 15-30BPM which cannot maintain life for any reasonable period of time, though it can help during some forms of arrhythmias which prevent the signal reaching the Purkinje fibers/Bundles of His. (6) This is also where take flight beats originate, and this is seen on the ECG as a widened QRS Complex.4. Discuss the role of decremental conduction in the AV node.Decremental conduction means the more the AV node is stimulated, the slower it conducts the stimulus. This allows a control over how fast the blood is pumped out. The faster the contractions, the less time between them for filling of the heart and therefore less blood is pumped out. (1) The AV Node slows down the stimulus so that there is an element of control of how fast the signal reaches the apex of the heart and prevents the ventricles from contracting so fast that the cardiac rig drops too low.(7) It is extremely important that the AV node is able to slow down the conduction velocity, even as it gets activated more and more frequently. It is even able to block out some signals. This is clearly seen in patients with atrial fibrillation. (7) The only way for the signal to travel to the ventricles is through the AV node (due to the insulating fibrous skeleton that prevents atrial cell ventricular cell depolarisation spread). (7) If the AV node allowed conduction of every single depolarisation, an atrial fibrillation would be fatal as the cardiac output would become too low, and the ventricle would go into ventricular fibrillation, which is fatal without intervention. It is the decremental properties of the AV node that prevent this from occurring. (7)5. Explain the term functional syncytium and its significance in the cardiac muscle contraction.A fun ctional syncytium by definition is a group of cells that are both mechanically and electrically bound to one another, so they are able to function as one. This is extremely important in cardiac muscle contraction.(1) One of the main reasons that the heart is able to work so effectively is that the contractions and depolarisations are always coordinated. (8) There is no coordination without communication, which are the electrical signals that are passed between the myocytes. (1) This extremely effective communication is completely unreal unless the cardiac myocytes are mechanically bound, so that when they do contract, it is as a whole. The specialization, which is unique to cardiac muscle, that allows it to be a functional syncytium is a structure called intercalated discs. (8) They contain three types of intercellular junctions many fascia adherens and desmosomes, for mechanical connection, and many gap junctions allowing for direct communication between neighbouring cells. (1) An other interesting property that contributes to the functional syncytium is the fact that cardiac muscle has an innate rhythmicity. This means that at the level of the muscle, the myocytes will exhibit the rhythm of the cell with the fastest rhythm. This makes regulating and coordinating the speed of the heart beat very easy and effective. (8)References1. atomic number 5 WF, Boulpaep EL. Medical Physiology Internet. Elsevier wellness Sciences 2008 cited 2014 Apr 9. Available from http//books.google.com/books?id=HlMJRw08ihgCpgis=12. Watkins MW, LeWinter MM. Physiologic role of the normal pericardium. Annu Rev Med Internet. 1993 Jan cited 2014 Apr 94417180. Available from http//www.ncbi.nlm.nih.gov/pubmed/84762383. Futami C, Tanuma K, Tanuma Y, Saito T. The arterial blood supply of the conducting system in normal human hearts. Surg Radiol Anat Internet. 2003 Apr cited 2014 Apr 925(1)429. Available from http//www.ncbi.nlm.nih.gov/pubmed/128199494. Shade BR, Wesley K. Fast and Easy ECGs Internet. McGraw-Hill Higher Education 2007 cited 2014 Apr 9. Available from http//books.google.com/books?id=hibqIAAACAAJpgis=15. Adams MG, Pelter MM. Ventricular escape rhythms. Am J Crit Care Internet. 2003 Sep cited 2014 Apr 912(5)4778. Available from http//www.ncbi.nlm.nih.gov/pubmed/145034336. Vassalle M. On the mechanisms underlying cardiac standstill Factors determining success or misery of escape pacemakers in the heart. J Am Coll Cardiol Internet. Journal of the American College of Cardiology 1985 Jun 1 cited 2014 Apr 95(6)35B42B. Available from http//content.onlinejacc.org/article.aspx?articleid=11113077. Cardiac Electrophysiology From Cell to Bedside 5th edition ISBN 9781416059738 US Elsevier Health Bookshop Internet. cited 2014 Apr 9. Available from http//www.us.elsevierhealth.com/cardiology/cardiac-electrophysiology-from-cell-to-bedside-expert-consult/9781416059738/8. Cardiac Muscle histologyolm.stevegallik.org Internet. cited 2014 Apr 9. Available from http//histol ogyolm.stevegallik.org/node/146