Readings

• Myocardium is lined with endothelium on the inner surface and epicardium on the outer surface
• Ventricular pressure rises a lot during isovolumetric contraction because all 4 cardiac valves are closed.
• EF is calculated by dividing SV by EDV
• Normal EF is 60 to 80 % while heart failure is considered if its less than 40%
• Isovolumetric relaxation occurs when semilunar valves close and then ends when AV valves open
• ventricles have 4 phases: isovolumetric contraction, ejection, isovolumetric relaxation and diastolic filling
• Pressure changes in the aorta during a cardiac cycle are partially dependent on the elasticity of the aorta. A stiffer aorta results in higher systolic and lower diastolic pressures
• Driving pressure thru coronary arteries is determined thru aortic blood pressure and right atrial pressure; P=ABP-RAP
• In most people the right coronary artery perfuses the right ventricle, AV/SA nodes and the right atrium
• The LAD and the circumflex perfuse the left atrium and ventricle
• Myocardial cells of the heart act as a syncytium because they are joined by gap junctions within intercalated discs that allow the flow of ions from one cell to the next
• Cardiac myocytes are terminally differentiated cells incapable of mitosis
• Lusitropy(muscle relaxation) occurs due to the removal of Ca+ from the cytoplasm; this process requires ATP
• Creatine phosphate is an immediately available stored from of energy that's used when ATP is low. It's converted to ATP by the enzyme creatine kinase
• Spontaneous generation of action potentials is determined by the progressive leak of Na+ and Ca+ into the cells. PSNS increases the efflux of K+ to slow the rate while SNS increases the influx of Na+ and Ca+ to speed up the rate
• Factors that can increase heart rate are baroreceptors detecting low BP, acidemia detected by chemoreceptors, atrial/ventricular distention and emotions
• Stroke volume is affected by preload as an increased stretch results in a more forceful contraction
• Increased afterload decreases stroke volume