cardiomyocytes | My Assignment Tutor

1—Pri2RMIT Classification: TrustedLearning objectives.Describe the features of cardiomyocytesDescribe how electrical signals are conducted through the heart.Describe the mechanical events of the cardiac cycle, and explain how these relate to theelectrical events in the heartIdentify the different parts of the electrocardiogram (ECG), and relate these to electricalevents in the heart.Describe common ECG abnormalitiesEssential Readings: Craft, Gordon, Huether, McCance and Brashers, Chapter 23Alterations in cardiovascular function across lifespan, Understanding Pathophysiology 3rdEdition, 20183RMIT Classification: TrustedThe Human Circulatory systemThe human circulatory system is a closedloop with unidirectional flow. It has three basiccomponents:• Heart the pump that generates thepressure gradient for blood flow• Blood vessels the passages throughwhich blood is directed• Blood the transport mediumThe human CV system comprises two loops.The pulmonary circulation carries bloodbetween the heart and lungsThe systemic circulation carries bloodbetween the heart and other organ systems34RMIT Classification: TrustedPathway of blood through the heart1.Deoxygenated blood enters the rightatrium (RA) viaSuperior vena cava (SVC)Inferior vena cava (IVC)2. When the tricuspid valve opens, itenter the right ventricle3. When the pulmonary semi lunarvalves open, the blood is ejected fromthe right ventricle into the pulmonarytrunk and pulmonary arteries into theLungs4. Blood is oxygenated in the lungsoxygenated blood enter the5RMIT Classification: TrustedPathway of blood through the heart5.Oxygenated blood enter theleft atrium via the pulmonaryveins7. When the Bicuspid valveopens, blood will enter the leftventricle8. Once the aortic semilunarvalves open, the blood will enterthe Aorta and the systemiccirculation6RMIT Classification: TrustedFeatures of cardiomyocytes62013 Pearson Education IncCardiomyocytes have a single centralised nucleusThey are striated, branched and 1/3 of the volume of thecell consists of mitochondriaIntercalated discs: electrically and mechanicallyconnect cardiac cells togetherGap junctions: allow action potential to be spreadbetween cellsDesmosomes: cell-to-cell adhesion that link cellstogether so forces can be transferred between cells7RMIT Classification: TrustedFeatures of cardiomyocytes72013 Pearson Education IncThere are two types of cardiomyocytes:99% are contractile1% form conduction system with the ability to self- excite8RMIT Classification: TrustedCardiac muscle contracts withoutinnervationAutorhythmic cells/ Pace maker cellsspontaneously generate action potentialsHeart can contract without an outsidesignal.This is known as myogenic contraction.Autorhythmic cells and contractile cellshave distinctly different action potentials.89RMIT Classification: TrustedCardiac muscle contracts withoutinnervationAutorhythmic cells have:An unstable resting potential(pacemaker potential).They slowly depolarise untilthey reach the threshold foraction potential firing.910RMIT Classification: TrustedContractile cells102013 Pearson Education Inc11RMIT Classification: TrustedCardiac contractile cellsAction potential are characterised by an extended plateau phase of theaction potential.They have a long refractory period (during which additional action potentialscannot be generated).This long refractory period prevents tetanus in cardiac muscle.Why is this important for cardiac function?Contractile cells usually don’t fire their own action potentials.What causes them to fire an action potential?11Silverthorn7th Editi12RMIT Classification: TrustedElectrical conduction in the heartRMIT University School of Health and Biomedical Sciences 12Conduction system – allow co-ordinated contraction of both atria and bothventricle13RMIT Classification: TrustedElectrical conduction in the heartRMIT University13Silverthorn7th EditionSinoatrial (SA) nodeAtrioventricular (AVnode) in base of atriumBundle of His ininterventricularseptumR& L bundle branchesPurkinje fibres in bothventriclesSinoatrial (SA) nodePace makerLocated in the R. atrium wallFires the fastestAutorhythmic cells contactspontaneously andrhythmically to fire AP (90-100times/min)Regulated by ANSRelays impulse to AV node14RMIT Classification: TrustedElectrical conduction in the heartRMIT University14Silverthorn7th EditionSinoatrial (SA) nodeAtrioventricular (AVnode) in base of atriumBundle of His ininterventricularseptumR& L bundle branchesPurkinje fibres in bothventriclesThe AP is passedrapidly via internodalpathway to the AVnodeSlowly through thecontractile cells of atria15RMIT Classification: TrustedElectrical conduction in the heartRMIT University15Silverthorn7th EditionSinoatrial (SA) nodeAtrioventricular (AVnode) in base of atriumBundle of His ininterventricularseptumR& L bundle branchesPurkinje fibres in bothventriclesConduction through theAV node is much slowerthan through otherpathways. Why?16RMIT Classification: TrustedElectrical conduction in the heartRMIT University16Silverthorn7th EditionSinoatrial (SA) nodeAtrioventricular (AVnode) in base of R.atriumBundle of His ininterventricular septumR& L bundle branchesPurkinje fibres in bothventriclesAtrioventricular nodeDelay in conduction toallow atria to contract17RMIT Classification: TrustedElectrical conduction in the heartRMIT University17Silverthorn7th EditionSinoatrial (SA) nodeAtrioventricular (AVnode) in base of atriumBundle of His ininterventricularseptumR& L bundle branchesPurkinje fibres in bothventriclesDepolarization of theventricles begins at theapex.Why don’t the electricalsignals spreaddownwards through theventricles from the AVnode?18RMIT Classification: TrustedElectrical conduction in the heartRMIT University18Silverthorn7th EditionSinoatrial (SA) nodeAtrioventricular (AVnode) in base of atriumBundle of His ininterventricularseptumR& L bundle branchesPurkinje fibres in bothventriclesDepolarization of theventricles begins at theapex.By contracting from thebottom upwards, bloodis driven towards thepulmonary artery andaorta at the top ofventricle19RMIT Classification: TrustedMechanical events in the cardiac cycle19Depolarization of the various parts of the heart triggers contraction (mechanical activityfollows electrical activity).There are several mechanical events in the cardiac cycleEach phase is characterized by:Particular changes in chamber pressure and volume.Pressure changes trigger the opening and closing of cardiac valves ( important formaintaining one way flow)Remember:Blood flows from an area of high pressure to an area of lower pressure.Contraction increases pressure inside a chamber; relaxation decreases pressure insidea chamber.20RMIT Classification: TrustedMechanical events in the cardiaccycle20Silverthorn7th Edition1.Atrial and ventricular diastoleHeart is at rest, both atria and ventricles arerelaxed and filling with bloodAV valves are open,Semilunar valves are closed.2.Atrial systoleAtrial depolarization triggers atrial contractionAdditional blood is pushed from the atria tothe ventricles.The ventricles are still relaxed and filling.21RMIT Classification: TrustedMechanical events in the cardiaccycle21Silverthorn7th Edition3. Isovolumic ventricular contractionDepolarization spreads to the ventriclesVentricular contraction begins.Increase in ventricular pressurePressure inside the ventricles >pressurein the atria= AV valves close.Pressure in the ventriclesSemilunar valves stay closed22RMIT Classification: TrustedMechanical events in the cardiaccycle22Silverthorn7th Edition4. Ventricular ejectionPressure in the ventricles >pressure in theaorta/pulmonary artery =Semilunar valves will open.Blood flows out of theventricles and into thesearteries23RMIT Classification: TrustedMechanical events in the cardiaccycle23Silverthorn7th Edition5. Isovolumic ventricular relaxationVentricle repolarize (relax).Decrease in ventricular pressurePressure in the ventricles 100bpmCauses: Increased oxygen requirements ie exercise, anxiety, fever, stimulants and illegal orprescription drugs, shock following AMISymptoms: shortness of breath, heart palpitations, dizziness, faintingResult: Faster heart rate = shorter filing time= decreased stroke volumeECG:Regular atrial and ventricular ratesP waves are normal, upright, and precede each QRS complexWhen very rapid the P waves may encroach on the T wave5556RMIT Classification: TrustedQuestion 3Mr Jonas has had fever for 2 days. Explain what his ECGindicates.A. Ventricular fibrillationB. Atrial fibrillationC. Sinus tachycardiaD. Ventricular tachycardiaE. Asystole57RMIT Classification: TrustedQuestion 4What is the problem with sinus tachycardia?Faster heart rate = shorter filing time= decreased strokevolume and decreased CO58RMIT Classification: TrustedQuestion 5Corin Jones is stabbed and suffers a haemorrhage. Shesuffers from hypovolaemia. Her ECG indicatesA. Ventricular fibrillationB. Atrial fibrillationC. Sinus tachycardiaD. Ventricular tachycardiaE. Asystole59RMIT Classification: TrustedAsystoleDefinition: No electrical activity in ventricle and leads to no cardiac outputCauses: H& Ts (Acidosis, Hypovolaemia, hypoxia, hyper or hypokalaemia,Hypoglycaemia, tension pneumothorax thrombosis )Most often seen following cardiac arrest with ineffective resuscitationECG:Known as the ‘arrythmia of death’, also called ‘flat line’ MEDICALEMERGENCY5960RMIT Classification: TrustedQuestion 5Corin Jones is stabbed and suffers a haemorrhage. Shesuffers from hypovolaemia. Her ECG indicatesA. Ventricular fibrillationB. Atrial fibrillationC. Sinus tachycardiaD. Ventricular tachycardiaE. Asystole61RMIT Classification: TrustedQuestion 6Mr Kyriacou has a myocardial infarction. What does hisECG indicateA. Ventricular fibrillationB. Atrial fibrillationC. Sinus tachycardiaD. Ventricular tachycardiaE. Asystole62RMIT Classification: TrustedVentricular tachycardia (VT)Definition: Abnormal electrical signals in ventricle lead to ventricular rate exceeding100bmpCause: Myocardial ischaemia/infarction, coronary heart disease, valvular heartdisease, cardiomyopathy, electrolyte imbalances, some drugsResult: Heart does not fill properly with blood and decreased cardiac output MEDICALEMERGENCY, Shockable rhythmSymptoms: Short of breath, dizziness and chest painECG:The P wave is absent and The QRS complex is wide and bizarre6263RMIT Classification: TrustedQuestion 6Mr Kyriacou has a myocardial infarction. What does hisECG indicateA. Ventricular fibrillationB. Atrial fibrillationC. Sinus tachycardiaD. Ventricular tachycardiaE. Asystole64RMIT Classification: TrustedQuestion 7What is happening to the ventricle in ventriculartachycardia?65RMIT Classification: TrustedQuestion 7What is happening to the ventricle in ventriculartachycardia?Abnormal electrical signals in ventricle lead to ventricularrate exceeding 100bmp66RMIT Classification: TrustedQuestion 8What is the problem with ventricular tachycardia67RMIT Classification: TrustedQuestion 8What is the problem with ventricular tachycardiaHeart does not fill properly with blood and results indecreased cardiac output

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