1 9 1 Circulatory Systems Evolution and Physics BIO 361T Fall 2014 1 Nematoda is the only phylum of terrestrial animals that lack circulatory systems all others are aquatic Porifera Cnidaria Platyhelminthes Why is it more common in aquatic animals than terrestrial animals to lack a circulatory system Less need for transport as nutrients are more abundant in environmental medium of water than air 2 Circulatory systems have several basic functions a Why do cells need O2 For oxidation reactions and to accept electrons at the end of oxidative phosphorylation in cellular respiration b Why do cells have CO2 that they need to get rid of It is a by product of cellular respiration where glucose is metabolized Energy is transferred to electrons and used to make ATP while the carbons are stripped off and released c Constant blood flow supplies O2 and removes CO2 What cellular processes would be affected if this did not occur Be as detailed as possible If O2 were low or CO2 built up cellular respiration would be inhibited Oxidative phosphorylation could not occur without oxygen and cell would go into anaerobic respiration instead lactic acid fermentation in the case of humans creating much less ATP per glucose Oxidation reactions would be inhibited d Where does this O2 come from Where does the CO2 go It comes from either the water or air around the animal but it ultimately comes from photosynthetic organisms mostly algae in water plants on land The CO2 gets released into the air through the respiratory surface skin gills lungs and used by photosynthetic organisms to capture sunlight energy e Where do the amino acids and glucose come from Animal s diet these are products of metabolizing the macromolecules in food e g protein for amino acids and carbohydrates for glucose f Where do the organic waste molecules go They get filtered out of the blood and excreted 2 3 Do circulatory systems share many basic functions because they all share a common ancestry or is this an example of convergent evolution Provide evidence to support your answer Convergent evolution many instances of open circulatory systems and closed circulatory systems throughout animal evolution which suggests it has evolved independently many times Also the anatomy of the systems is highly variable which on its own could just be extensive adaptation but along with the phylogenetic data suggests convergent evolution It is not surprising they would evolve with the same basic functions as all eukaryotic cells share basic functions of cellular respiration and are based on the same molecular components 4 Rewrite the law of bulk flow in a way that includes the factors that determine the resistance of the circulatory system We can use this equation to roughly predict how fluids will flow through the circulatory system in units of volume that move past a given point per unit time like L min Poiseuille s equation which is a more detailed version of the law of bulk flow just substitute in formula for R Q P r4 8L For each question that follows specify what variables are being affected a How will vasodilation affect the bulk flow of blood Mathematically why is a small change in vessel radius sufficient to elicit a large change in blood flow r increases which decreases R which increases Q Because it is to the 4th power b The radius of capillaries is very small Explain why this alone will decrease the velocity of blood flow through capillaries This makes R larger which makes Q smaller which makes V smaller It is harder to push a fluid through a straw than a pipe It will take longer to push through the same volume of fluid due to this increase in resistance c Why is this advantageous How does A change in capillary beds to decrease velocity even further Because diffusion exchange occurs in the capillaries If the blood flows through this area too fast there will not be enough time for diffusion to occur Cross sectional area is greater in capillaries than arterioles because there are so many Lower Q and higher A both make V smaller d As temperature decreases fluid viscosity increases How will colder environmental temperatures affect bulk flow Assume no compensatory responses by the animal Higher increases R which decreases Q Blood will flow slower in colder temperatures e How does increasing the length of the capillaries affect resistance to blood flow through the capillary bed as a whole L increases R f Is this similar to adding resistors in series or parallel in an electrical circuit In series 3 g Will this increase or decrease the velocity of blood flow If R increases Q will decrease which will decrease V h How will this affect the rate of diffusion in the capillary bed overall In Fick s Law the length of the capillary is the surface area over which diffusion occurs A If A increases Q rate of diffusion also increases If they conclude that diffusion will increase if velocity decreases that is fine but they should also use Fick s Law here They need to understand what A and L are in Fick s Law See 5 i What variable corresponds to the thickness of the blood vessel wall L in Fick s Law j How do the thin walls of capillaries affect the rate of diffusion Compose a statement that explains this effect Because L is small Q will be high If substances do not have to diffuse very far they will get there faster 5 Explain how A and L in models that apply to blood flow differ from A and L in models that apply to diffusion Because they are concerned with movement in perpendicular directions Diffusion is across the blood vessel wall In Fick s Law A is the area over which diffusion occurs the length of the blood vessel wall L is the length or distance over which diffusion occurs the thickness of the blood vessel wall Blood flow is down the blood vessel In those models A is the cross sectional area through which the blood flows L is the length over which the blood flows or the length of the blood vessel 6 Using the metaphor of an electrical circuit explain why the blood pressure is close to zero in the veins of humans Capillary beds are like resistors in series length of capillaries and resistors in parallel multiple capillaries that branch from the same arteriole When these add up they cause a decrease in signal strength pressure or current 7 If there is no blood pressure in veins how does the blood return to the heart Other pumps external pumps like skeletal muscle and peristalsis in blood vessels
View Full Document
Unlocking...