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Lecture 9

BIO271 Lecture 9 heart notes.doc

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Chris Garside

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Fish hearts how do chambers contract and how can we ensure unidirectional control? valves are very important in controlling things, but there are no valves in the sinus venosus out to the body tissues, but there is a valve between the atrium and sinus venosus, a valve between the atrium and ventricle, and there is a valve between the ventricle and the bulbus arteriosus. So contraction of each of these chambers in sequence, save the sinus venosus. Sinus venosus is very thin walled and doesnt contract very much at all. If it did, some of the blood might flow into the atrium and some of it might flow back into the circulatory system. The sinus venosus is very important in fish for initiating a heart beat. They contract in sequence; one way valves. the valves can open in one single direction, this is important for unidirectional flow. Once the pressure in the ventricle increases, the valve to the atrium closes but it cant open to the atrium, whereas the valve to the bulbus aretriosis opens and therefore blood flows out into the bulbus arteriosis. The bulbus arteriosis is somewhat compliant, it accepts a large volume of blood, serves as a pressure resevoir, similar to what our aorta does. It reduces the variations in blood pressure, it accepts a larger volume of blood and pushes that blood out into the system as it recoils, maintaining a relatively constant flow in pressure. Amphibians they have a spongy myocardia. consider the fact that they have three chambers and one ventricle. That means that two supplies of blood are being sent to one ventricle. Oxygenated blood from pulmonary and deoxygenated blood from the systemic. This is perfect because the spongy myocardia is not highly vascularized. The fact that oxygenated blood finds its way to the entire ventricle can supply oxygen to the spongy myocardial myocytes. if there is only a single ventricle, how can they keep oxygenated and deoxygenated blood separate? they do this with 1)the trabeculae within the ventricle and 2) the spiral fold in conus arteriosus (elasmobranchs). The conus arteriosus is now divided here, we now have the pulmocutaneous artery and the systemic artery. The spiral fold is very imp
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