Physiology of the heart I.

Transcription

1 Physiology of the heart I. Features of the cardiac muscle The cardiac cycle Theheart as a pump Cardiac sounds (Learning objectives 35-36) prof. Gyula Sáry Cardiovascular physiology Cardiac function, pumping activity of the heart Cardiac cycle Characteristics of the cardiac muscle Electrophysiology of the heart The normal electrocardiogram (ECG) 2 1

2 Things to consider: blood flows downhill, follows a pressure gradient pressure gradient is generated by the heart the heart can not store blood what comes in, must get out the circulation is a closed loop valves in the heart only play a passive role the heart must cope with different needs 3 Cardiac, skeletal and smooth muscles 4 2

3 Characteristics of skeletal, cardiac and smooth muscle cross striated muscles Characteristics skeletal muscles cardiac muscles smooth muscles Thickness µm µm 5-10 µm Length up to 20 cm (M. sartorius) µm µm Nucleus many, on the periphery one central nucleus one central nucleus Organization of the contractile fibres parallel, in sarcomers parallel, in sarcomers no sarcomers, net-like meshwork Neuronal supply somatic nerves autonomic nerves autonomic nerves Communication between cells no fast, through gap junctions through gap junctions 5 Physiologic anatomy 1. sarcomers (~ 2 μm) sarcomers covered with sarcolemma = cardiac muscle fibre T-and axial tubular system, sarcoplasmic reticulum mitochondria(sarcosomes, 30% of the myocardial cells) capillaries(up to 4000/mm 2 ) 6 3

4 gap junctions Physiologic anatomy2. (connexon, 6 subunits, 2 nm space to passions) longitudinal conduction is veryfast gap junctions at end-to-end no transversal gap junctions functional syncytium 7 Action potential lengths in the excitable tissues Refractory periods 8 4

5 Tetanic contraction in skeletal muscle NO tetanic contraction in cardiac muscle 9 potential (mv) fast depolarization plateau phase repolarization intracell. time (ms) membrane extrtracell. permeability time (ms) 10 5

6 Electromechanical coupling in the myocardiac cell Ca Ca ++ and cardiac muscle contraction; extracellular Ca ++ acts as a trigger 12 6

7 Stimulation and inhibition of Ca ++ channels beta receptor stimulating G protein cell membrane muscarinergic receptor inhib. G protein Ca2+ channel open cardiac muscle cell 13 Contraction of the myocardium no external neural impulse, automatic gap junction---very fast conduction allthe fibres contract-unlike in skeletal muscles AP and contraction lasts for hundredsof ms Ca ++ also from extracellular space (trigger) removal: Ca ++ pumpsand Ca ++ antiporter contraction force depends on Ca ++ symp. stimulation extracellular Ca ++ increase cardiac glycosides 14 7

8 15 The cardiac cycle 16 8

9 left ventricular pressure bal kamrai nyomás time[s] Pressure changes during the cardiac cycle bal kamrai térfogat 17 right atrium right ventricle left ventricle left atrium 18 9

10 left ventricular pressure (mmhg) ejection isovolumetric relaxation isovolumetric contraction left ventricular volume (ml) filling 19 The cardiac cycle Systole isovolumetric contraction maximal (rapid) ejection decreased ejection Diastole isovolumetric relaxation rapid filling slow filling atrial contraction (0.8 sec) 0.27 sec 0.53 sec 20 10

11 Blood volumes during the cardiac cycle end-diastolic volume (EDV): ml stroke volume (SV): ml end-systolic volume (ESV): ml ejection fraction: SV / EDV ~ 50-70% increasing stroke volume: increasing the EDV and/or decreasing the ESV 21 The valve-plane mechanism valve plane in systole shifts down ejection of blood the valve plane in diastole moves back ventricular filling 22 11

12 The atria contribute to the diastolic filling of the ventricles % of the blood volume flows directly through the atria into the ventricles atrial contraction ( atrial systole ) can contribute 20-25% (increases effectiveness and speed of filling) under normal conditions atrial systole has only minimal importance heart rate & exercise 23 Function of the valves A-V valves prevent backflow during systole semilunar valves prevent backflow during diastole the valves act passively! 24 12

13 The jugular pulse Fluctuations in the right atrial pressure cause pressure oscillations in the jugular vein. Physiologically only visible during increased venous pressure (weight lifting, Valsalva manouvre). 25 carotid pulse jugular pulse 26 13

14 Normal jugular venous pulse: A, a positive wave due to contraction of the right atrium; C, a positive deflection due to bulging of the tricuspid valve toward the atria at the onset of ventricular contraction; X, a negative deflection due to atrial relaxation during the ventricular systole; V, a positive deflection due to filling of the right atrium against the closed tricuspid valve during ventricular contraction; Y, a negative deflection due to emptying of the right atrium upon ventricular relaxation. 27 The heart as a pump stroke volume x heart rate=cardiac output cardiac output =blood volume leaving the ventricle in 1 minute ~ 5.5l/min cardiac index = cardiac output/body surface ~ 3.1l/m 2/ min 28 14

15 Since the time of Hippocrates (5th Century BC) doctors usually placed their ears on a patient's chest to listen to the heartbeat and lung sounds. Faced with a breasty woman, Dr Rene Laennec modestly insisted on using a rolled-up sheet of paper as shown on picture.thus, in 1816, the first stethoscope was conceived. 29 Aorta valve: 2R2 Pulmonary valve: 2L2 Tricuspidal valve: 4-5R1 Mitral valve: 5L6-8 15

16 Cardiac sounds auscultation on the chest 1. (systolic) sound: contraction, valves, ejection of blood 2. (diastolic) sound: valves, can be split 3. (diastolic) sound: cuspidal valves during rapid filling 4. (late diastolic) sound: atrial contraction