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BIOA02 Module 2 (Lectures 5 and beyond)

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

1BIOA02 2012Lecture 5 Hearts and Circulatory Systems1 The Composition of BloodBlood consists of a fluid component called plasma and a cellular component consisting of red blood cells erythrocytes and white blood cells cells involved in the immune system the buffy coatIn a human approximately 55 of the blood volume is plasma The remaining 45 are the cells See pages 897 to 899 in the textbook Blood cells originate from a blood stem cell These stem cells can form myeloid stem cells which in turn differentiate into red blood cells which contain haemoglobin and carry oxygen see lecture 7 platelets involved in clotting and granulocytes details in lecture 12 The stem cells can also form lymphoid stem cells which ultimately differentiate into Blymphocytes Tlymphocytes and Killer TCells details in lecture 12Red blood cells contain the respiratory molecule haemoglobin Haemoglobin consists of 4 peptide subunits 2 alpha and 2 beta Each of these subunits contains a heme group In the center of the heme group is an iron Fe atom that binds oxygen more on this in lecture 722 The Fish HeartThe fish heart consists of 4 chambers in series ie one following the other Venous deoxygenated blood enters the heart through the sinus venosus Although considered to be part of the heart the sinus venosus is technically part of the venous system Blood then flows through the sinoatrial valve into the atrium a very thinwalled chamber Blood then passes through the atrioventricular valve into a muscular ventricle Finally blood moves through the bulbal valve into the bulbus arteriosus The atrium and the ventricle are both contractile but most of the contractile force arises from the ventricle The bulbous arteriosus can also be considered as part of the arterial system It functions as a Windkessel vessel This means that it expands fills with blood and bulges outward when the heart is contracting and then collapses back into its initial shape when the heart is relaxing This helps force blood through the arteries when the heart is relaxingQuestion What blood vessel in humans serves the same purpose as the bulbous arteriosus ie acts as a Windkessel vessel3 Circulation in Gill Water Breathing FishDeoxygenated blood from the tissues systemic circulation returns to the heart through the venous system It is then pumped through the ventral aorta VA to the gills where it is oxygenated Oxygenated blood leaves the gills via the dorsal aorta DA and flows into the systemic circulation The circulation is therefore a single loopheart to VA to gills to DA to systemic circulation arteries then veins back to the heart Blood must be pumped across two capillary bedscapillaries in the gills and capillaries in the systemic circulation Therefore the heart must generate sufficient pressure to drive the blood through the entire circuit while simultaneously having a low enough pressure to prevent pressureinduced damage to the delicate gill tissue34 Circulation in the LungfishAlthough the lungfish is a fish its circulatory system resembles that of a mammal much more than it resembles the circulation of a regular fish Deoxygenated blood returns to the heart from the tissues It is then pumped through the gills to the lungs where it is oxygenated Oxygenated blood returns to the heart from the lungs It is then pumped through the gills to the systemic circulation tissuesAlthough the heart is not completely divided like a mammalian or avian heart it functions as if it were divided Note that the gills play very little role in gas exchange since they are much reduced in sizeThe diagram below provides slightly more anatomical detail although it is basically identical to the diagram above Start at the lungs Oxygenated blood in red flows from the lungs to the heart via a pulmonary vein This oxygenated blood then flows through some of the blood vessels in the gills branchial vessels before entering the dorsal aorta From there this oxygenated blood flows to the tissues Deoxygenated blood from the tissues in blue flows to the heart through several blood vessel in the gills into the pulmonary artery and then to the lungsFor the purposes of exam questions the patterns of flow in the diagram above are what you should know The diagram below is just to illustrate that there is more complexity than can be seen in a general diagram such as the one above Compare the lungfish circulation to that of a human and convince yourself that despite some Exerciseanatomical differences they are basically the same
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