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Physiology of Cardiac Muscle and Electrical Activity of the Heart Denny Agustiningsih.

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Presentasi berjudul: "Physiology of Cardiac Muscle and Electrical Activity of the Heart Denny Agustiningsih."— Transcript presentasi:


2 Physiology of Cardiac Muscle and Electrical Activity of the Heart Denny Agustiningsih


4 Cardiac muscle Denny Agustiningsih

5 Two Types of Cardiac Muscle Cells Ordinary: make up 95%- 99% of all heart muscle cells.  Also called worker cells or contractile cells  Biochemically similar to red skeletal muscle  Slow to fatigue Specialized: make up remaining 1%-5%  Also called autorhythmic or automatic cells  Responsible for initiation and/or transportation of electrical impulses through the heart  pacemaker potential Denny Agustiningsih

6 CONDUCTION SYSTEM Denny Agustiningsih Sinoatrial Node Atrioventricular Node

7 Electrical Conduction SA node - 75 bpm ◦ Sets the pace of the heartbeat AV node - 50 bpm ◦ Delays the transmission of action potentials Purkinje fibers - 30 bpm ◦ Can act as pacemakers under some conditions

8 Denny Agustiningsih Membrane Potential (mV) 0 -40 -60 Time (msec) Depolarization Spontaneous Threshold Potential Ca ++ in K + out Ca (T-type) Na K parasymphathetic symphathetic

9 Denny Agustiningsih

10 HEART RATE Normally : 60-100 bpm > 100 bpm : tachycardia < 60 bpm : bradycardia Denny Agustiningsih

11 Resting heart rate is about 60-100 beats/min (lower in athletes because they have large stroke volumes) The HR can be increased about 3 times in exercise exercise Above about 200 beats/min the heart would not have time to fill properly  therefore nature limits the rate Rate is controlled by the autonomic nervous systemautonomic nervous system Denny Agustiningsih

12 Extrinsic Influences Autonomic nervous system Hormonal influences Ionic influences Temperature influences Denny Agustiningsih

13 Control of Heart by ANS Sympathetic innervation- ◦ + heart rate ◦ + strength of contraction ◦ + conduction velocity Parasympathetic innervation ◦ - heart rate ◦ - strength of contraction ◦ - conduction velocity Denny Agustiningsih

14 Autonomic nervous system modulates the frequency of depolarization of pacemaker Sympathetic stimulation (neurotransmitter = NE); binds to  1 receptors on the SA nodal membranes Parasympathetic stimulation (neurotransmitter = ACh ); binds to muscarinic receptors on nodal membranes; increases conductivity of K+ and decreases conductivity of Ca2+ How do these neurotransmitters get these results?


16 Major Hormonal Influences NE/E Thyroid hormones ◦ + inotropic ◦ + chronotropic ◦ also causes an increase in CO by  BMR Estrogen/ Testosteron Denny Agustiningsih

17 Ionic influences Effect of elevated [K+] ECF ◦ dilation and flaccidity of cardiac muscle at concentrations 2-3 X normal (8-12 meq/l) Effect of elevated [Ca++] ECF ◦ spastic contraction Denny Agustiningsih

18 Effect of body temperature Elevated body temperature ◦ HR increases about 10 beats for every degree F elevation in body temperature ◦ Contractile strength will increase temporarily but prolonged fever can decrease contractile strength due to exhaustion of metabolic systems Decreased body temperature ◦ decreased HR and strength Denny Agustiningsih

19 Direct Stretch on SA node Stretch on the SA node will increase Ca++ and/or Na+ permeability which will increase heart rate Denny Agustiningsih

20 Terminology Chronotropic (+ increases) (- decreases) ◦ Anything that affects heart rate Dromotropic ◦ Anything that affects conduction velocity Inotropic ◦ Anything that affects strength of contraction  eg. Caffeine would be a + chronotropic agent (increases heart rate) Denny Agustiningsih

21 mV +20 -90 0 Ca, K K out K out ∞ Ca in (L-Type) plateau Na in

22 AP of Contractile Cardiac cells Action potentials of cardiac contractile cells exhibit prolonged positive phase (plateau) accompanied by prolonged period of contraction ◦ Ensures adequate ejection time ◦ Plateau primarily due to activation of slow L-type Ca 2+ channels

23 Refractory period

24 Action Potential Skeletal Cardiac

25 Mechanism of Cardiac Muscle Excitation, Contraction & Relaxation Denny Agustiningsih Kalsium yg menginduksi pelepasan kalsium Hanya mengetuk pintu Pengeluaran kalsium salah satu caranya Na, Ca exchanger

26 Denny Agustiningsih mV +20 -90 0 4 0 1 2 3 Absolute Refractory period 0 400 200100300 Time (msec) Relative Refractory period Period of Supranormal excitability

27 Denny Agustiningsih

28 Modulation of Contraction Denny Agustiningsih


30 The Body as a Conductor This is a graphical representation of the geometry and electrical current flow in a model of the human thorax. The model was created from MRI images taken of an actual patient. Shown are segments of the body surface, the heart, and lungs. The colored loops represent the flow of electric current through the thorax for a single instant of time, computed from voltages recorded from the surface of the heart during open chest surgery.

31 The Modern ECG Machine Modern

32 If a wavefront of depolarization travels towards the electrode attached to the + input terminal of the ECG amplifier and away from the electrode attached to the - terminal, a positive deflection will result. If the waveform travels away from the + terminal lead towards the - terminal, a negative going deflection will be seen. If the waveform is travelling in a direction perpendicular to the line joining the sites where the two leads are placed, no deflection or a biphasic deflection will be produced. ECG examines how depolarization events occur in the heart

33 Denny Agustiningsih P Q R S T Serabut purkinje – ventrikel Nodus SA – atrium Atrium (ototnya lebih sedikit) Klw siklusnya atrium - atrial cyte Sirkulasi-peredaran darah Siklus-kontraksi dan relaksasi

34 Denny Agustiningsih P Q R S T

35 P Q R S T 0.5 Sec 1 sec

36 ECG Complexes


38 Kontraksi – sistol Ventrike kaknan-memoma darah ke paru Ventrikel kiri-memompa darah keseluruh jantung Pintu masuk – katub yang menghubgungkan dengan atrium (valam atrioventricualr) Pintu keluar kiri - aorta Pintu keluar kanan – katub pulmu\onal Tujuan awal kontraksi untuk membuka pintu keluar (aorta)

39 ECG Description ECG description ◦ amplitude (voltage)  recorded in mm  positive or negative or biphasic ◦ width (duration)

40 ECG in Perspective 1. ECG recording of electrical activity not the mechanical function 2. ECG does not depict abnormalities 3. ECG does not record all the heart’s electrical activity


42 Excitation-Contraction Coupling in Cardiac Contractile Cells Ca 2+ entry through L-type channels in T tubules triggers larger release of Ca 2+ from sarcoplasmic reticulum ◦ Ca 2+ induced Ca 2+ release leads to cross-bridge cycling and contraction

43 Frank-Starling Law Preload, or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volume

44 Extrinsic Factors Influencing SV Contractility is the increase in contractile strength, independent of stretch and EDV Increase in contractility comes from ◦ Increased sympathetic stimuli ◦ Hormones - epinephrine and thyroxine ◦ Ca2+ and some drugs ◦ Intra- and extracellular ion concentrations must be maintained for normal heart function

45 Figure 14-30 Modulation of Cardiac Contractions

46 Reflex Control of Heart Rate

47 Regulation of Cardiac Output Figure 18.23

48 Depolarisasi mendahului kontraksi Repolarisasi mendahului relaksasi Kontraksi jantung tidak melalui otak Listrik-otot atrium-kontraksi--ketika sampai di ventrikel-ventrike berkontraksi Gap junction Kontraksi otot jantung-otot pekerja Otot pekerja memiliki aktin & myosin Mendapat rangsang sehingga ion Repolarisasi = fase istrahat Kontraksi & relaksasi-aktin & myosin Sebagian kalsium pergi ke aktin & myosin untuk berikatan dengan troponin C, sebagian ke retikulum sarkoplasma Retikulum sarkoplasma-tempat penyimpanan ion calsium (ada pintu yang disebut.........., hanya terbuka untuk kalsium)-masuk ke sitosol Denny Agustiningsih

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