1、Weight of the heart 300g Work: 75/min, 10000 beats /day 35 million beats /year, 2.5 billion beats/life 70ml/beat, 7200 l/day,The work of the heart in one life is equivalent to lifting 30 tons to the Mount Everest,The busy and hard working heart!,Intercalated discs,Cardiac muscle tissue is striated w

2、ith the myocytes containing usually just one central nucleus and being connected to each other by intercalated discs,Function of intercalated discs: Interlock adjoining cells Prevent adjoining cells from pulling apart when heart contractsdesmosomes Ion flowgap junctions, to electrically stimulate ne

3、ighborsact as unit,心肌收縮的“全或無”現(xiàn)象,相鄰的心肌細胞是由閏盤連接，由于閏盤的特殊結(jié)構(gòu)和特性，興奮可以通過它由一個心肌細胞傳播到另一個心肌細胞。因此，整個心室（或整個心房）可以看成是一個功能上相互聯(lián)系的合胞體，產(chǎn)生于心室某一處的興奮可以在心肌細胞之間迅速傳遞，引起組成心室所有心肌細胞幾乎同步收縮。,Ca2+ release during Excitation-Contraction coupling,Action potential travels down T tubules,Voltage -gated Ca2+ channels activated, Ca2+ f

4、lows out SR into cytoplasm Ca2+ channels close when action potential ends. Active transport pumps continually return Ca2+ to SR,Ca ATPase (SERCA),Calcium induced calcium release, CICR,Skeletal Vs. Cardiac Muscle Contraction,Impulse generation: Intrinsic in cardiac muscle, extrinsic in skeletal muscl

5、e Plateau phase: Present in cardiac muscle, absent in skeletal muscle Refractory period: long in cardiac muscle, shorter in skeletal muscle Summation: Impossible in cardiac muscle, possible in skeletal muscle Extracellular calcium-dependent in cardiac muscle,Contractility,No tetanic contraction Simu

6、ltaneous contraction The contraction is reliant on exogenous Ca2+,Heart Valves,1. Atrioventricular a. tricuspid-between RA and RV; three leaflets b. Bicuspid-between LA and LV; two leaflets,2. Semilunar a. pulmonic-three leaflets b. aortic-three leaflets,Prevent backward regurgitation Provide low re

7、sistance to forward flow,Heart Valves,Systemic and Pulmonary Circulation,Heart Chambers,Cardiac Cycle,Diastole,Systole,I.The Cardiac Cycle Concept: The period from the end of one heart contraction to the end of the next,Properties: 1) Diastole is longer than systole 2) The sequence of systole and di

8、astole,2 The Phases of the Cardiac Cycle Period of isometric (isovolumetric or isovolumic) contraction,Events: ventricular contraction ventricular pressure rise atrioventricular valve close the ventricular pressure increase sharply Period: 0.05 sec Importance: enable the ventricular pressure to rise

9、 to the level of aortic pressure (after-load),(2) Period of ejection Events: ventricular contraction continuously the ventricular pressure rise above the arterial pressure semilumar valves open blood pours out of the ventricles,Rapid ejection period (0.10s, 70% of the stroke volume) Reduced ejection

10、 period (0.15s, 30% of the stroke volume),(3) Period of isometric (isovolumic) relaxation,Events: ventricular muscle relax the ventricular pressure fall lower than the aortic pressure aortic valve close the ventricular pressure fall sharply,Period: 0.06-0.08 s Importance: Enable the ventricular pres

11、sure fall to the level near the atrial pressure,(4) Period of filling of the ventricles Events: Ventricular muscle relax continuously the ventricular pressure is equal or lower than the atrial pressure atrioventricular valve open, blood accumulated in the atria rushes into the ventricular chambers q

12、uickly from the atrium to the ventricle.,Period of rapid filling. (0.11s, amount of filling, 2/3) Period of reduced filling (0.22s, little blood fills into the ventricle),(5) Atrial systole Significance, 30% of the filling During high output states or in the failing heart, the amount added by atrial

13、 contraction may be of major importance in determining the final cardiac output.,CARDIAC CYCLE,CARDIAC CYCLE,Atrial Systole,Mitral Closes,Isovolumic contract.,Aortic opens,S1,Rapid Ejection,Reduced Ejection,Isovolumic Relax.,Aortic closes,Rapid Ventricular Filling,Mitral opens,S2,Reduced Ventricular

14、 Filling,Atrial Systole,c wave, bulging of the A-V valves when the ventricles begin to contract,2） Pressure changes in the atria, the a, c, and v waves.,a wave, the atrial contraction,v wave, at the end of ventricle contraction, caused by the accumulated blood in the atria while the A-V valves are c

15、losed,The sounds heard over the cardiac region produced by the functioning of the heart.,Heart Sounds,Heart Sounds,S1- first sound Atrioventricular valves and surrounding fluid vibrations as valves close at beginning of ventricular systole,S2- second sound Results from closure of aortic and pulmonar

16、y semilunar valves at beginning of ventricular diastole S3- third sound is produced by vibrations of the ventricular walls when suddenly distended by the rush of blood from the atria,II Cardiac Output Stroke Volume The volume pumped by the heart with each beat, = end diastole volume（125ml） end systo

17、le volume （55ml）, about 70 ml 2. Ejection Fraction Stroke volume accounts for the percentage of the end diastolic volume, = stroke volume / end diastole volume X 100%, normal range, 55-65%,Left Ventricular Volumes - Definitions,End Diastolic Volume (EDV) Volume at the end of diastole (end of ventric

18、ular filling) End Systolic Volume (ESV) Volume at the end of systole (end of ventricular contraction) Stroke Volume (SV) = EDV - ESV Ejection Fraction (EF) = SV/EDV,Left ventricular norm: 62%,Ejection Fraction is the best indicator of heart performance and disease prognosis,3. Minute Volume, or Card

19、iac Output the volume of the blood pumped by one ventricle, = stroke volume X heart rate. It varies with sex, age, and exercise 4. Cardiac Index, the cardiac output per square meter of body surface area. the normalized data for different size individuals, the normal range is about 3.0 3.5 L/min/m2,Heart Work,Stroke work （kJ） =stroke volume (L) (mean artrial pressure-mean pressure of left atrium) 9.807,Determinants of Cardiac Output (CO),Preload,Heart Rate,Afterload,Contractility,Cardiac Output,Stroke Volume,Definitions,Preload amount of stretch on the ventricular myocard