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Cardiovascular Questions Due 2-28 1. Beginning at the superior vena cava, trace the path of blood on its journey through the heart, lungs, body tissues and back to the vena cava, naming all the chambers and vessels it passes through on its journey (you can omit the peripheral vessels, concentrating only on those that exit or enter the heart directly). (4) Vena cava - Right atria - Right ventricle - pulmonary trunk - Pulmonary artery - Lung capillary beds Pulmonary Veins - Left atria - Left ventricle - Aorta - Arteries - Arterioles - Tissue capillary beds - Veinules Veins - Vena cava 2. Why are there three major waves of the ECG? What events correspond to each of them? (4) Each wave represents a change in membrane potential across the heart. The P wave appears first, and is due to the propagation of an action potential, which was initiated by the sinoatrial node, across the atria to the atrioventricular node; it precedes a gentle atrial systole. The QRS complex appears second, and is produced by the rapid propagation of the action potential from the AV node, down the purkinje fibers and throughout the myocardium; it precedes strong ventricular systole. The T wave comes last, and is produced by the repolarization of the ventricles; this immediately precedes ventricular diastole. 3. What events are responsible for the first and second heart sounds? (2) The closing of the AV valves and the closing of the Semilunar valves 4. What is the Starling law? What property of heart muscle is responsible for it? (2) Starlings law states that the amount of ventricular stretch during diastole is directly proportional the the volume of blood that will be ejected during the subsequent systole; OR "more in = more out" 5. Increasing the plasma (interstitial / inter-cellular) Ca2+ concentration increases the strength of contraction of cardiac muscle but not of skeletal muscle. Why is there a difference? (2) The opening of Ca2+ channels on the plasma membrane of myocardial cells is a part of action potential propagation through cardiac muscle. If the extracellular Ca2+ levels are increased, more Ca2+ will enter the cell when those channels open. Therefore more troponin will bind Ca2+ ions, so more active sites on actin filaments will be exposed, more myosin filaments will bind, and a stronger contraction will result. 6. List 3 factors that determine the Resistance of a single vessel? (3) Viscosity, turbulence, and diameter. 7. The diameter of a capillary is smaller than that of an arteriole, yet collectively the capillaries have lower resistance than the arterioles. Explain how this is possible. (2) While much smaller than arteries and arterioles, the capillaries collectively provide far more area for the same volume of blood to pass through. This increased area results in a tremendous blood pressure drop in the capillaries. Since Flow is directly proportional to pressure, the resistance to flow in the capillaries is smaller than in the arterioles. 8. What effect would a decrease in venous compliance have on the volume of blood in the veins? On the venous pressure? On the venous return? On the total peripheral resistance? What effect would arteriole dilation have on the total peripheral resistance? On venous return? (3) Decreased venous compliance would reduce the volume of blood in the veins; increase venous pressure; decreases venous return; and increase the peripheral resistance. Arteriole dilation would decrease peripheral resistance and increase venous return. 9. Give two examples of how heart rate and/or blood pressure are controlled: what kinds of receptors are involved, what stimuli are they responding to, where are they located, and what part of the CNS receives the afferent sensory information? (4) Chemoreceptors located in the carotid sinus and the aortic arch, respond to lowered O2 levels or increased CO2 and blood pH levels. These sensors stimulate the cardiovascular centers in the medulla oblongata (brainstem) and increase cardiac output and vasomotor tone. Baroreceptors, located in the carotid artery and the aortic arch, respond to mechanical deformation (stretch). When BP drops, for example, these receptors stimulate the cardioregulatory center in the MO which increases sympathetic stimulation of the SA nodes of the heart and reduces parasympathetic stimulation of the myocardium; this increases cardiac output. It also stimulates vasoconstriction of the arteries and arterioles, which increases BP. 10. Why must arteries be very thick and elastic? Why can veins afford to be thinner and less elastic? (2) Arteries must handle a large volume of blood delivered at high pressure. Therefore they must be built to withstand high pressure expand, and regain their original shape. Veins do not deal with high pressure so they can be thinner and do not need to stretch as much.