Semilunar valves The semilunar valves open when the ventricles contract and the force of the blood Pushes the semilunar valves open and blood enters the arterial trunks. The valves Close when the ventricles relax and the pressure in the ventricle becomes less Than the pressure in a great arterial trunk. Blood in the arteries begins to fall Backward toward the ventricle and is caught in the cusps of the semilunar valves, And they close. The closure of the semilunar valves prevents blood flow back into The ventricle. 23. Comparison of skeletal vs cardiac muscle Cardiac muscle Skeletal muscle short long Fat-thick thin Branched and vary in diameter-interconnected Cylindrical fairly constant in diameter-independent 1-2 nuclei centrally located Multinucleated nuclei located just under sarcolemma-peripherally located. Striated-less of a banding pattern Striated-clear banding pattern Involuntary control Voluntary control Interlocking cells-causes impulse to spread from cell to cell Independent fibers-impulses do not spread from cell to cell Large mitochondria 25-35% of volume of the cell Smaller mitochondria only 2% of the volume of the cell Sarcoplasmic reticulum is simpler, lacks large terminal cristae Sarcoplasmic reticulum is more complex Some cells (1%) self excitable autorhythmicity Must be stimulated by nerve ending Relies almost exclusively on aerobic respiration Can still contract under anaerobic conditions for extended periods 24. What factors have an effect on cardiac output? p. 761 Cardiac output is influenced by both heart rate and stroke volume. Heart rate is altered by Stimulation of the SA node and the AV node. Stroke volume is altered by changes to the Myocardium, which include an increase or decrease in stretch of the heart wall (preload), the Amount of Ca2+ in the sarcoplasm caused by inotropic agents, and changes in resistance (afterload) in the arteries that must overcome for the heart to eject blood. -Chronotropic agents (alter SA node and AV node) a) positive agents increase heart rate b) negative agents decrease heart rate -Inotropic agents (alter Ca2+ levels in sarcoplasm) a)positive agents increase stroke volume b) negative agents decrease stroke volume
-Venous return (volume of blood returning to the heart) is directly correlated with stroke volume -Afterload (increased resistance in arteries) is inversely correlated with stroke volume 25. The flow of the blood through the heart Blood flow through pulmonary circulation: (transports blood from the R side of the heart to the alveoli of the lungs for gas exchange & Back to the left side of the heart) 1. Deoxygenated blood enters the right atrium from the vena cavae and coronary sinus 2. Blood passes through the right AV valve (tricuspid valve) 3. Blood enters the right ventricle.