1 / 40

Chapter 10 The heart as a pump

Chapter 10 The heart as a pump. Section 1 The contractility of the heart. The ultrastructure of cardiac muscle Sarcomere is similar with skeletal muscle Intercalated disks, gap junctions between cells Rich in mitochondria

howard
Download Presentation

Chapter 10 The heart as a pump

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 10 The heart as a pump

  2. Section 1 The contractility of the heart

  3. The ultrastructure of cardiac muscle • Sarcomere is similar with skeletal muscle • Intercalated disks, gap junctions between cells • Rich in mitochondria • Under-developed sarcoplasmic reticulum (SR), contraction is dependent on [Ca2+]o (CICR)

  4. 2. The excitation-contraction coupling of cardiomyocyte • The process which connects excitation and contraction • Triggered by Ca2+ influx • CICR, Ca2+ transient • Cardiocyte contraction induced by Ca2+ • Ca2+ reuptake and relaxation: Ca2+ pump of SR

  5. Membrane potential ICal current Ca2+ transient Cell shortening

  6. Excitation-contraction of cardiomyocyte Action potential of cardiomyocyte  Ca2+ influx via L-type Ca2+ channel  Ryanodine receptor of SR  CICR,Ca2+ release of SR  Ca2+ binds to troponin  Myofilament sliding  Cardiocyte contraction

  7. The characteristis of heart contraction 1. Dependence on [Ca2+]o Source of sachoplasmic Ca2+: ICal (Ca2+ influx) (10%) CICR: Calcium-induced calcium release (Ca2+ influx stimulates ryanodine receptor) (90%) 2. “All or none” contraction(全或无式收缩） The atrium and ventricle are two functional syncytia (机能合胞 体）,just like two cells. 3. No complete tetanus (不产生完全强直收缩) ERP is very long, the heart is non-responsive to any stimulus during contraction and early relaxation.

  8. Section 2 The pumping function of the heart

  9. Cardiac cycle （心动周期） • The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called cardiac cycle. • Each cycle is initiated by spontaneous generation of an action potential in the sinus node. • The conduction delay in the A-V node (>1/10sec) allows the atria to contract ahead of the ventricles, thereby pumping blood into the ventricles before the strong ventricular contraction begins. Thus, the atria act as primer pumps(初级泵）for the ventricles.

  10. The characteristics of a cardiac cycle • Diastole is longer than systole • Heart rate mainly affects diastole

  11. Time sequence of the events in a cardiac cycle Atrial systole  Ventricular systole Isovolumic contraction phase Rapid ejection phase Reduced ejection phase  Ventricular diastole Isovolumic relaxation phase Rapid filling phase Reduced filling phase

  12. Figure 10-3 Events of the cardiac cycle for LV function, showing changes in LA pressure, LV pressure, aortic pressure, ventricular volume, ECG, and the phonocardiogram.

  13. Function of atria as primer pumps • Atrial contraction usually causes an additional 25% filling of the ventricles; 75% of the blood flows directly through atria into the ventricles. • The heart usually can continue to operate even the atria stopping work unless a person exercises.

  14. Heart sound （心音） • The first heart sound: represents the beginning of ventricular contraction. • The second heart sound: represents the beginning of ventricular dilation. • The third heart sound: heard at the end of ventricular rapid filling, caused by the vibration of ventricular wall and papillary muscle, found in some children, young people and HF. Gallop rhythm (奔马律): all the above 3 sounds appear. • The forth heart sound (atrial sound): heard before the first heart sound, caused by atrial contraction and ventricular filling, usually can not be heard, found by phonocardiogram at the decrease of ventricular wall compliance.

  15. Cardiac murmur （心脏杂音） • Systolic murmur • Diastolic murmur • Phonocardiogram （心音图）

  16. Section 3 The evaluation of cardiac pumping function

  17. stroke volume (ml) EF =  100% ventricular end diastolic volume (ml) • Stroke volume （每搏输出量） • The blood output in each contraction of LV or RV, about 70ml at resting condition in an healthy adult. • Ejection fraction （射血分数，EF） • Minute volume (cardiac output) 　（每分输出量, 心输出量） Cardiac output = stroke volume  heart rate

  18. Cardiac output (L) CI = Body surface area (m2) 5 - 6 (L) = 1.6 - 1.7 (m2) = 3.0 – 3.5 L/min/m2 • Cardiac index （心脏指数） CI: 10 years old: 4 normal adult ≥ 3 80 years old 2

  19. Stroke work （每搏功，搏功） Stroke work (J) = stroke volume (L)  ejection pressure + kinetic energy of blood flow

  20. 心脏作功量 心室收缩一次所做的机械功称为搏功 W=∫ PdV（压力-容积功 ） ＋∑1/2v2dm （动力功） V2为舒张期末容量， V1为收缩期末容量 ，P为心室内压，V为心室容量 v为血流速度，m为射出血液的质量 W=PV＋1/2mv2 P为主动脉平均血压，V 为每搏输出量， v为平均血流速度 剧烈运动时m和v显著增大， 动力功不能忽略 W=PV v2v1

  21. 心脏作功效率（外功/心脏耗氧量） 心脏消耗内能（主要通过有氧代谢）  外能  热（降低作功效率）   功  内功（非有用功： 等容收缩、心率过快等）  外功（和泵血直接有关的有用功） 容量功：内功所占比例低，效率高 压力功：内功所占比例高，效率低 如动脉压升高，心室扩大

  22. Section 4 Cardiac Reserve

  23. The capacity of cardiac output of a healthy adult: • At rest: 5 L/min • Maximum: 25-30 L/min • Maximum of a well-trained athlete: 35 L/min

  24. The components of cardiac reserve • Stroke volume reserve: At rest: 70 ml Maximum: 105-110 ml (including end diastolic volume reserve 25 ml, end systolic volume reserve 15-20 ml) • Heart rate reserve Maximal HR: 160-180 beats/min Too fast HR will decrease the cardiac output

  25. Section 5 Factors that affect cardiac pumping function

  26. Preload （前负荷） • Cardiac preload can be reflected by the ventricular end diastolic pressure, or, initial length (初长度）. • Heterometric autoregulation (Frank-Starling mechanism of the heart) (异长自身调节）： The greater the heart muscle is stretched during filling, the greater the force of contraction and the greater the quantity of blood pumped into the aorta. In other words, within the physiologic limits, the heart pumps all the blood that comes to it without allowing excessive damming of blood in the veins.

  27. Ventricular function curve reflects the relationship between preload and pumping function. The curves do not have downward branch

  28. The mechanisms of Frank-Starling law: (1)The effective overlapping degree of thick filaments and thin filaments of the sarcomere; (2) The affinity of troponin to Ca2+ depends on the length of muscle.

  29. The preload is affected by venous retuning volume and end systolic ventricular volume: Four factors determine the venous retuning volume: ventricular filling time venous blood retuning speed The pressure of pericardial cavity The compliance of the ventricle

  30. Afterload （后负荷） • Cardiac afterload can be reflected by the stretching force of the ventricular wall at systole, or the peripheral resistance (外周阻力）. • An increase in afterload will decrease cardiac output

  31. Cardiac contractility （心肌收缩能力） • An intrinsic factor • Affected by neurohormonal factors • Independent of pre- or afterload

  32. Heart rate （心率）

  33. 正常心脏 心脏扩大

  34. Role of atria in the pumping funtion of heart 1. As a tract of blood returning Increased ventricular pressure Dysfunction of atrial contraction Decrease in atrial compliance ↓ Decrease in veinous blood retuning ↓ Increase in atrial pressure 2. As a primary pump (初级泵) (主动充盈作用, 在心室被动充盈障碍时尤为重要)

More Related