BME 265 2014 Homework 3.docx

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University of Miami
Biomedical Engineering
BME 265
Edward Dauer

Kyle Merino 4/5/14 BME 265 Homework #3 Chapter 13 1. Explain in detail the cardiovascular cycle from atrial diastole to ventricular diastole. Include the relationship between S1 and S2 heart sounds, interventricular pressure, and volume including isovolumetric phase of contraction and relaxation. The first stage is atrial systole in which the atrioventricular valves (AV valves) are open allowing the ventricles to be begin filling up with blood while the semilunar valves are closed. In the second stage, isovolumetric contraction occurs when theAV valve and semilunar valve are both closed and the ventricles begin to contract; the closing of theAV valve produces the first heart sound (S1). The third stage, Ventricular ejection, is when the semilunar valve is open while the AV valve is closed and when the pressures in the left and right ventricles exceed aortic and pulmonary pressure. The fourth stage, Isovolumetric relaxation, is when both theAV valve and semilunar valve are closed allowing the ventricles to relax and the pressure drops until it reaches atrial pressure; the closing of the semilunar valve produces the second heart sound (S2). Finally, ventricular filling, the fifth stage, occurs when theAV valves open again while the semilunar valves are closed allowing the ventricles to fill with about 70% of their final volume and the atria expand and fill with blood. 2. Explain the different parts of the EKG including the P, QRS, and T waves. How do they relate to depolarization and repolarization of the atria and ventricles? The P wave is the first little hill in an electrical heart signal. This happens in response to atrial depolarization causing atrial contraction. It usually lasts about 80 milliseconds. The QRS wave or complex is the highest peak of the signal and corresponds to the depolarization of the right and left ventricles. This part lasts between 80 and 120 milliseconds. The T wave represents the recovery or repolarization of the ventricles and is the last considerable hill in the signal. However, there does exist a U wave immediately after the T wave, which is very tiny and almost negligible. 3. Describe the electric conducting system of the heart from the SAnode to the purkinje fibers and myocytes. What is the importance of the delay at the P-R interval? The sinoatrial node (SAnode) is a group of specialized cardiomyocytes that sit on top of the right atria and generate impulses and therefore it is known as the pacemaker of the heart. Purkinje fibers are a group of specialized cardiomyocytes that surround the ventricles and are able to conduct cardiac action potentials. Myocytes are typical cells found in muscle tissue and are found in the heart because the heart, itself being a muscle, has to use contractile force to expel and intake blood at the proper time. The P-R interval serves as an indicator of atrioventricular conduction time. As people get older, this interval gets longer. It may also lengthen due to the heart block or acute rheumatic fever. The interval also shortens with increased heart rate. Chapter 14 4. What is EDV, SV, and ESV? What is afterload and preload? Explain the Frank-Starling law of the heart and how it relates to increased contractility caused by sympathetic nerve stimulation. EDV stands for End Diastolic Volume and this is the amount of blood filling in to the left or right ventricle in diastole. SV stands for Stroke Volume and is the volume of blood pumped from one ventricle every beat. ESV stands for End Systolic Volume and is the volume of blood left in a ventricle at the end of systole or before diastole. The preload is the amount of work on the heart prior to contraction, which is directly proportional to the stroke volume. The afterload is the amount of pressure generated in the ventricles required in order to eject blood; it must be greater than the pressure in the arteries to work properly. Because contraction strength is directly proportional to end diastolic volume, the Frank-Starling Law dictates that a rise in peripheral resistance will cause a decrease in stroke volume of the ventricles leading to greater end diastolic volume for the next cycle thereby increasing the contraction strength to eject more blood. 5. How is blood volume regulated by bothADH and aldosterone secretion? ADH (Anti-Diuretic Hormone) is released by the posterior pituitary gland when osmoreceptors detect an increase in plasma osmolality. If the person is dehydrated or
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