1 9 2 Circulatory Systems Vertebrates BIO 361T Fall 2014 1 Arteries are able to constrict and dilate as are arterioles to a lesser degree Are the arterioles that lead to capillary beds of different organs in series or in parallel Why is this important In parallel which allows the body to control the flow of blood to organ systems independently by dilating and constricting different arterioles 2 Why can arteries constrict and dilate to a greater degree than veins How will this affect the volume and speed of blood flow Substantial smooth muscle layer in the tunic media Changing radius r changes resistance to blood flow R which negatively correlates to bulk flow and velocity of blood flow Both are innervated by sympathetic input Overall sympathetic input increases cardiac output systemic vascular resistance and arterial blood pressure This is done by constricting arteries and arterioles increase R which increases arterial BP and decreases downstream blood flow and constricting veins decrease r which decreases amount of blood veins can hold and increases venous BP pushing blood forward for heart to pump 3 Relate the lack of radius regulation to the presence of valves in veins Veins cannot regulate radius so they cannot move blood via pressure gradients without external pumps like in skeletal muscle One way valves prevent blood from flowing backwards 4 What is the function of arteries closest to the heart having more elastic fibers in their tunica media and arteries farther from the heart having more smooth muscle Prevents breaking when pressure from heart is high Exerts high pressure to propel blood into systemic tissues When blood enters smaller vessels arterioles resistance is higher and blood will tend to get backed up Elastic recoil of larger arteries like the aorta which is directly connected to the ventricle of the heart pushes blood forward 5 Nitric oxide is a gaseous neurotransmitter that causes smooth muscle relaxation by increasing the second messenger cGMP which is quickly broken down by phosphodiesterases in the cell a How would nitric oxide affect arterioles Relaxation of tunica media vasodilation b Viagra is a drug that prolongs vasodilation in the arterioles of the penis Propose a molecular mechanism for how Viagra works Explain why Viagra can prolong an erection but not cause one Blocks a phosphodiesterase preventing cGMP catabolism cGMP remains high in the arteriole smooth muscle cells so vasodilation is prolonged sustaining an erection once it has begun Requires cGMP to already be high 6 Using Fick s Law identify all of the variables that change in capillaries relative to other vessels and explain how each one makes diffusion more efficient A is maximized by length of capillaries and capillaries in parallel L is minimized by only endothelial layer of cells 2 7 True or false If false provide a counter example a Arteries always transport blood away from the heart True this is how arteries are defined b Veins always transport blood towards the heart True this is how veins are defined c Arteries always transport oxygenated blood False pulmonary artery carries deoxygenated blood from right ventricle to lungs d Veins always transport deoxygenated blood False pulmonary vein carries oxygenated blood from lungs to left atrium 8 Some fish have a small caudal heart in addition to the central systemic heart a Given its name roughly where is this accessory heart located relative to the systemic heart Towards the tail it is in the tail which is technically the caudal fin in a fish b Why do you think there has been positive selection for this in fish but it is absent in vertebrates that have evolved more recently Gills and tissues are in series in fish so heart encounters more resistance than in animals with double circulation where blood returns to heart to be re pumped between lungs and systemic tissues Caudal heart gives pressure a boost 9 Amphibians and reptiles can control how much blood is shunted through their pulmonary vs systemic circuits a Explain why water breathing fish cannot do this Do not have separate circuits b Explain how amphibians and non crocodilian reptiles can do this Ventricles are only partially separated If pressure is high in tissues pressure will be higher in ventricle that pumps to them so blood will be diverted more to other side c Explain how crocodilian reptiles can do this Ventricles are fully separated but there are two aortas One of the aortas connects to the right ventricle like the pulmonary artery so deoxygenated blood can be shunted to the pulmonary or systemic circuit d Why might this control be advantageous in amphibians and non crocodilian reptiles They breathe intermittently some dive for long periods e Why might this control be unnecessary thus not providing an advantage in birds and terrestrial mammals They breathe fairly continuously 3 10 Explain how birds and mammals can be thought of as having two hearts Their ventricles are completely separated The left side of the heart operates the systemic circuit and the right side operates the pulmonary circuit 11 The completely separated pulmonary and systemic systems in birds and mammals allow the pressures of these systems to be regulated independently Hypothesize as to why this is advantageous Able to increase pressure in systemic circuit to increase distance traveled and maximum possible body size However this increase in the pulmonary circuit might cause fluid to leak out and increase distance that particles must diffuse so lower pressure is better in this circuit
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