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Feb 17th2012_PhysioII.docx

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Kinesiology & Health Science
KINE 2011
Gillian Wu

th Feb 17 , 2012 Human Physiology II Systemic Pressure Gradient Vascular network is like upside down tree. -One big massive root is aorta that distributes all the blood that came from left ventricle That aorta branches into smaller arteries. -Then the arteries branch off further. --The blood gets ejected into aorta (75ml normal) has to travel down to aorta, but gets distributed to thousands of arterioles and millions of capillaries. -The graph is showing what happens to pressure as you move from left ventricle to all the way to circulatory system (arteries, arterioles, capillaries, to veins and back to heart again) -Pressure in left ventricle oscillates whilely , we have diastolic pressure of approx. 0. -Complete oscillation occurs through this entire process --As soon as the blood gets into aorta, that changes , now we have systolic pressure that continues to match what the left ventricle has initiated (120mmHg) Now we will never see diastolic pressure dropping to 0 it stays high (80mmHg) --Feature of circulatory system (diastolic pressure never drops down) Pressure in arteries continues to oscillate (change) -As the blood moves through the large , there is no change in pressure in aorta.-Will be same if measured since there is no loss of pressure occurring -If the blood goes to the smaller blood vessels we will see a steep drop in blood pressure.The arterials are the site in the circulation where you see a largest decrease in PRESSURE due to their characteristic ability to regulate where blood goes, (gatekeeper role in activiely determing diameter, resistance direction of blood) -Capillaries, blood pressure goes down further and all way back to right atrium where its 0mmHg. -Pressure is always going from higher to lower point. The pressure gradient that drives flow from the left ventricle to the right atrium. This pressure gradient is why we don’t have blood flowing opposite dirtection. Blood goes with the pressure gradient. --There is NEVER NO FLOW, but it does increase and decrease in the amount. -The oscillation continues in the arterials but by the time it gets into capillaries and veniules there is NO DETECTABLE ossciallations and pressure. You only have 1 pressure to measure. If you measure pressure in capillary, you would not get any indiactino of cardiac cycle.You would not be able to detect effect of siastole and diastole. You needto be in the larger vessels and most easily in the arteries, to see shifting cardiac pressure. ARTERIES= Conduit Vessels Conduit = good at moveing blood from one location to another, do it rapidly and without much resistance. In order for arteries to distribute blood they need to have large diameter ( to hold large vol of blood) - Low contractile( contraction is an active process , arteries have layers special type of muscles surround them, vascular smooth musles, When would it be a good time for AORTA to contract? NEVER , you always want these arteries to be relaying the blood as easily possible. -High distensible (PASSIVE FEAUTRE, Compliant if you apply pressure how much it would stretch out) -You need it so when blood pumps from ventricles into arteries, arteriest can capture vol of blood and handle it well. These things allow them to be low resistance vessel. (ie taking EXPRESS LANE) ARTIERIES need to be strong to withstand the high pressure ( high systolic pressure) to prevent rupture. Elasticity (distensible) SYSTOLE -Left ventricle will be pumping blood into aorta, -A typical stroke vol is 75mL of blood is being squeezed into aorta during systole (0.3 sec) 300ms (normal cardiac cycle at rest) -What happens to blood when to come to aorta? Some of the blood will keep shooting down to the rest of the vascular system. Therefore since this is large vol some of it will be pushing on the walls of aorta, since the aorta is elastic and it will stretch out. - Some vol blood is allowed to stay in aorta during systole and help to push the walls of aorta to push it more open for larger vol of blood -This elastic feature is very imp in maintaining reasonable pressure in the arteries because there is this relationship between amount of vol the blood has to occupy to the pressure it’s going to create by occupying that space. - If we could take the 75mL of blood and put it in aorta with the smaller diameter (the smallest one will have the HIGHEST PRESSURE). As the 75mL comes in, aorta helps to minimize the increasing pressure with having the blood pushed into it. If aorta was not able to stretch out like that, that blood will be confined to smaller diameter and pressure will go higher. THIS DISTENSIBLITY (ELASTICITY) HELPS MAINTAIN THE LOWER SYSTOLIC BLOOD PRESSURE. -This is PASSIVELY stretching out, DIASTOLE -Left ventricles stop contracting, no more blood coming from left ventricle, no blood entering. We have chance for blood to exit,. This is an open network and blood will continuously flowing downstream where there is lower pressure following its pressure gradient… There will be less of distensing pressure on aorta, and aorta will tend to come back to its original size. (PASSIVE not CONTRACTION) -Walls of aorta were stretched out and now it rebounds back to its original size -This is occurring when the heart is not pumping blood ( no blood entering vascular system but its continuing to flow out of aorta into the downstream network. This is where we convert intermittent pump every so often into a continuous flow through the rest of the network (which means all the hardworking cells in the body are going to see continuous delivery of oxygen and nutrient rich blood, they don’t have to wait for next systole to provide them the blood. -We are able to now maintain a continuous flow through the rest of vasculature. -The aorta is doing this in large part due to the distensibility. What is it structurally that allows the aorta to do this? Because of very large amount of protein called Elastin Elastin= organized in these concentric rings in the walls of aorta, Cross-section of aorta Lumen will have blood Thick wall and black lines are wings of elastin -The amount and organization of protein is the most important Elastin has a structure which has many connective pieces put together which allows them to be folded up like an accordion (instrument) under unstressed state, then if you put pressure
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