1、Chapter 10The heart as a pumpSection 1The contractility of the heart 1.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 (C
2、ICR)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 SRMembrane potentialICal currentCa2+ transientCell shorten
3、ingq Excitation-contraction of cardiomyocyteAction potential of cardiomyocyteCa2+ influx via L-type Ca2+ channelRyanodine receptor of SRCICR,Ca2+ release of SRCa2+ binds to troponinMyofilament slidingCardiocyte contractionThe characteristis of heart contraction1. Dependence on Ca2+oSource of sachopl
4、asmic 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
5、 heart is non-responsive to any stimulus during contraction and early relaxation.Section 2 The pumping function of the heart u 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 spon
6、taneous 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.
