in lecture b of chapter 18 we now are going to talk about different circulatory routes within the circulatory system so the first thing that we'll talk about again are the anastomosis so these vascular anastomosis we know that these are bridges or connections on that can occur around the blood vessels so an anastomosis will begin to connect vessels together and that pathway and that connection is now referred to as collateral vesicle vessels meaning again that these pathways exist between different types of vessels so the first anastomosis is known as an arteriole anastomosis most organs are going to possess this especially the heart and the brain and we find it around joints because again it's very hard and a movable joint for the blood supply to be delivered like it should so these anastomosis the arteriole are very much necessary for the joint areas and also the heart and the brain itself we know that new anastomosis can be formed if an artery becomes inefficient with meeting the metabolic needs of the tissue that it's in so we see this a lot of times we've mentioned with the coronary arteries that if there is a blockage a simple blockage or a single blockage an anastomosis already exists by nature and if there's insufficient blood supply new vessels can grow around the blockage or around the hindered or hampered area venous anastomosis are the most common type of all so these are where veins begin to be connected together by smaller collateral so these collateral vessels connect neighboring veins we know that they become very intertwined and very complex and form complex web-like patterns throughout that tissue throughout that organ and again these are the responsibilities for trying to drain and get the deoxygenated blood back out of the tissue and back up to the heart and then finally you have the arteriovenous and so this is where an artery bypasses a capillary and it automatically goes into a vein without passing through the capillary itself so it's an artery to vein which is usually called a shunt so if you notice with simple circulatory routes and you need to understand this and be able to describe what would be the most simplest that we know the heart of course would allow the arteries to take the blood out the systemic pathway the arteries then wind up in arterioles arterioles we know and we mentioned earlier feed into capillaries venules then allow the blood to come out of the capillary and then the different structures of veins leads you back up to the right side of the heart so again a he and the figure shows you a simple capillary bed then you have the portal system like the hypophyseal portal system between the hypothalamus and the anterior pituitary remember you had several capillary beds in unison so one capillary bed fed into the other one creating the portal system we said that another name for an arterial venous anastomosis is a shunt it bypasses the capillary entirely so we see shunts used in Dallas's patients and in blocked arteries they'll put in a shunt a lot of times to bypass the area that is not working or is hindered but then we said the other two differences would be a venous anastomosis were vessels within the veins form these collateral pathways and then on the arterial side you can have the arterial anastomosis where the same thing happens interconnection between the arteries and we said especially in the brain and the heart these arterial anastomosis are going to form now we need to talk about hemodynamics for just a little bit so this is all about the tendency of the blood to flow throughout the cardiovascular system so there's some foundational concepts that we need to cover before we actually get into this one of those are gradients so we've already talked about that great it's exists as diff says between high pressures and low pressures so there can be concentration gradients pressure gradients or electrical gradient so there's a high side and a low side with solutes and concentrations there's also high and low sides with ions and electrical gradients that exist but we're focusing on the pressure gradient which is defined as the heart's tendency to force and drive the blood into the blood vessels and then of course out into the tissues so it creates these pressure gradients as the chambers of the heart are going to affect on the volume so pressure of course is going to be highest so you need to commit this to memory the pressures are going to be higher the closer you are to the heart so in that simple pathway we said we go from heart to artery start aureoles the capillaries to venules to veins and back to the heart so the arteries of course that are near the heart are going to have the highest pressure those that as you move further away from the heart in that cycle you're going to decrease the blood pressure so blood we know goes down this pressure gradient from areas of higher pressure that are very close or near the heart to areas that are lower pressure which are out in the peripheral vasculature which is the peripheral on the capillary and the venules and the veins so if you notice we've mentioned earlier and in class that the artery of course they order is going to have the highest pressure on the venous side the inferior vena cava is going to have the lowest pressure so they order the highest the inferior vena cava the lowest and as far as blood flow we can calculate and understand how much blood is actually going into the tissues per minute so we consider this to be blood flow and I've mentioned the term perfusion and also the rate of the flow itself so we know that whatever cardiac output is blood flow should match that and we know cardiac output for the average person is about five to six liters per minute so remember the total amount pumped out of the ventricles per one minute is the definition for cardiac output so there's two factors that relate back to blood flow so notice it's directly proportional to pressure gradient so if there's not a gradient you're not going to have flow you've got to have a high side and a low side and that pressure gradient so that means that the blood flow will increase when pressure gradients increase and they would decrease if the pressure gradient decreases so these are directly proportional to each other directly proportional flow is directly proportional to the pressure gradient if one increases the other increases if one decreases the other decreases but notice flow is inversely proportional to resistance so if resistance goes up and this is the tendency of the blood to flow so if resistance goes up blood flow would decrease as resistance decreases blood flow would increase so make sure that you understand that pressure gradients and resistance control the amount of blood that can flow out into the tissues and the organs as far as blood pressure we know that this is the outward force from the lumen on the vessel wall so we know that we can express it as millimeters of mercury and you have the two pressures that are recorded notice the systolic pressure is related to ventricular systole so when the ventricles are contracting that's that highest pressure and remember I had to get above eighty which was the pressure of the order so that the blood would flow from the left ventricle into the aorta so usually considered to be around 120 normally in the average young adult the diastolic pressure is when the ventricles are in diastole they're relaxing between heartbeats and this should be a minimum arterial pressure of about 75 it used to be 120 over 80 but now most textbooks in nursing and healthcare and also a lot of anatomy books refer to 120 over 75 the dalek of the diastolic pressure in millimeters of mercury is the normal average for a young adult in good health we know that the vasculature we've already said will influence how the different parts are and how much blood is moving through the body so that we know that this can vary depending on what part of the vasculature we're in are you in an artery or in a vein so you notice that the highest of the blood pressure is in the large systemic artery so we saw already said earlier it would be they Horta the lowest lar on the large systemic veins would have the lowest pressure so the vena kv arm would have the lowest pressures because they're leading right back to the right side of the heart that's the furthest part in that simple blood flow before you get back to the right atrium so if you notice there's three main factors so we said there's two values that influence blood pressure and blood flow but there's three factors that influence blood pressure so resistance cardiac output and blood volume so if you analyze the figure resistance which is known as peripheral resistance is determined by the vessel length that will talk about the diameter of the vessel the viscosity of the blood the ability of it to flow obstructions in the vessel themselves would all determine how much peripheral resistance you would have so out in the periphery out in the tissues usually considered to be in the veins you have varying amounts of peripheral resistance remember the two things that determine cardiac output are your heart rate times your stroke volume so how much blood is ejected from the ventricles in one heartbeat would be the stroke volume and then how many what's your heart rate per minute and that determines your five liters five to six liters of cardiac output and then finally blood volume is determined by two things the amount of water loss versus the amount of water gain so a dehydrated person of course runs the risk of their blood pressure dropping off but we already have talked about that's why antidiuretic and aldosterone hormones act to retain the salt or retain the water on so that the blood pressure and the blood volume maintain stable levels so notice then we said the three things peripheral resistance cardiac output and blood volume then directly effect and determine blood pressure so this is a great graphic organizer that your textbook has to try to relate all this material together so first let's talk about peripheral resistance so first by definition it is the impeding of the blood to flow out in the vessels so it's stoppage or something that's going to resist the blood to flow into the vessel we know again that vessels that are near the heart arm have little resistance while those that are further away from the heart would have higher resistance so out in the peripheral portion of the body that's why we call it peripheral resistance so notice as the resistance increases blood pressure increases we've already said that they're directly proportional resistance is determined by three different variables we said so go back to that original figure we said the first thing was vessel diameter so as the radius increases or you can dilate the vessel there's less resistance and that's going to allow the resistance to the blood to flow would also would decrease so as the vessel increases the radius the resistance is going to decrease so this is the quickest variable that your especially your arteries arm can control again to maintain homeostasis with your blood pressure by influencing the vessel radius and the lumen it can either constrict or vasodilate to do that it can change blood pressure the quickest or the fastest the viscosity defined as the resistance that all liquids have to flow usually you think of viscosity with your engine in your car so we add oil to cut down on the friction and the oil is graded to pay depending on how much viscosity is in the oil so the more expensive oils for your car that would have more viscosity or higher viscosity more viscous so again the more viscous the liquid is notice that says the molecules will resist being put into motion or they'll resist staying in motion so blood seems to have a relatively high viscosity because of all of the formed elements and the proteins that are in the plasma so if you have high viscosity that can of course affect blood pressure versus low viscosity so what are they doing when they try to lower blood pressure a lot of times they'll try to again influence how viscous the blood is the last thing that can determine resistance was vessel length so notice that the longer that the blood vessel is the greater resistance it will have so that means that it's going to need and require more pressure to propel the blood through a longer vessel than one that's short so this is because you see resistance in the pulmonary circuit is much much lower than the systemic circuit the vessels that are in the pulmonary circuit because the lungs are so close to the heart those vessels are much shorter than the ones that are out in the systemic circuit that go all the way down into the lower extremities so vessel length determines blood pressure pressures are greater and they have greater resistance if they are long it allows more area if you have a long vessel for friction to build up and resistance to build up a fourth factor that can influence peripheral resistance we'll be those obstructions that could be there so this could be tumors in a vessel it could be the plaque that builds up so from the plaque or the blocked arteries the blood clots that spontaneously form of course all those would have struck the lumen and thus affect blood pressure so that's where a lot of times people that have high blood pressures they go and they look for some of these conditions like obstructions there's something also to consider here blood that's flowing in a vessel is said to have layered or laminar flow so if you notice this I usually describe it in class as if you have several people trying to go down one small hallway the ones that are in the middle of the line usually can go faster than the ones that are close to the wall why because they get hung by the friction on the wall and they get hung by things that are near the wall but the ones that are in the middle are more freely to move so by increasing laminar flow larger vessels are going to have higher laminar flow than smaller vessels so there's less of the vessel wall for friction to build up or four things to adhere to on so vessels that are larger are usually going to have blood that flows much more freely so here you see that in a the very large artery and notice the arrows show that most of the lumen is allowing those middle layers of the fluid to flow quite readily and quite speedily but in a small smaller blood vessel you have more contact with the vessel wall and it begins to slow it down it begins to be that resistance we talked about the second thing that can influence blood pressure was cardiac output so again we know that cardiac output is determined by stroke volume how much blood is pumped with every heartbeat and the heart rate so it's stroke volume times heart rate per beats per minute so both of those of course can affect if you have a little volume in the blood so your stroke volume goes down of course you're not going to have very high cardiac output so it's going to be harder to perfuse and allow blood flow into the tissues if your heart rate slows down yeah the course can affect it the same way so we know that cardiac output peripheral resistance are the two factors that will determine pressure gradients within the vessels themselves and these gradients will drive circulation so the textbook tells you how to figure that out where Delta P refers to the pressure change cardiac output times peripheral resistance so notice when the cardiac output increases blood pressure increases when cardiac output decreases the blood pressure begins to drop and decrease the final thing we talked about was blood volume so by losing too much water out of the body or over flooding the body we can influence blood pressure so someone that creates hypotonic urine their drinking water water water they don't drink a lot of electrolytes they can actually go into fluid overload opposite of that is if we lose too much water in our urine too many electrolytes the water is going to follow those electrolytes and of course that would decrease our blood pressure so total volume of the blood is directly linked to the amount of water that's in the blood plasma so if the blood contains more water of course the volume is going to increase and as blood volume increases the blood pressure will increase and then vice versa small increases in blood volume notice that says that there's Abel there's the system itself the circulatory system has variables or properties that will offset the ability to stretch within the vessel itself and this is known as compliance so how compliant the tissue is is its ability to offset the vessels to stretch so we know that veins out of all of the different vessels are the most compliant because again they'll collapse they're very pliable they can accommodate fluid when the blood pressure increases but even though their volumes increase in the blood pressure is only going to rise a small amount but if this happens in the arteries of course you're going to see large changes in the blood pressure so if we notice different portions of the circulatory system we've already said that in the pulmonary circuit you have blood pressure that's fairly low so usually 10 millimeters or less than telling millimeters of mercury so notice veins 5 to 0 venules 15 to 5 millimeters of mercury however on the systemic circuit the blood pressure is going to change significantly as blood travels the further away from the heart so again the pulmonary circuit on average around 15 millimeters of mercury the systemic 95 millimeters of mercury so if you notice in the arteries especially um we said they order in those large arteries you got a 100 millimeter 120 millimeters of mercury systolic 80 millimeters of mercury diastolic pressures so very high pressures on the systemic side very low pressures on the pulmonary side as far as calculations and the circulation throughout the system we know that the pressure would decline in venules and then eventually into veins could drop to 4 millimeters of mercury in the inferior vena cava it says to even zero in the right atrium and that again is why you don't need valves between the vena cava and the right atrium because there's not high pressures in those vessels for the blood to try to backflow there's low pressure is going to be due to again these veins we said have very high compliance they have declining resistance because you're going larger as you go from venules to medium veins and then large veins you're increasing the lumen you're increasing the diameter so venous blood has to be returned to the heart at the same rate that it's pumped out on the arteries and the arterial side so this allows venous circuits to be under very very low pressures and that of course is going to allow other things to be a driving force to actually get the venous blood back to the heart so we'll analyze some things that can affect venous return so we're leaving the blood capillary in the veins the venules the veins and we'll talk about things that can control venous return but in this section we talked about that collateral vesicles are known as anastomosis and we talked about the different types of those I gave you the simplest circulatory route if you talk about the heart to the arteries to the arterioles leading into the capillary venules leading out into the different structures and types of veins and then back to the heart and again notice then that that is the most simplest form we talked about gradients and how they influence blood flow especially pressure gradients and then we talked about the three things that can influence blood flow or actually the two things there on that first slide we talked about that influence blood flow itself we talked about two types of blood pressure the systolic the high pressure when the ventricles are contracting are in Sicily and the diastolic pressure when the vent vent rolls are in diastole and we said on average for a normal healthy young adult it's usually 120 over 75 millimeters of mercury the that have the highest and lowest pressures we said they order would have the highest the vena cava would have the lowest the three things that affect blood flow we said resistance cardiac output and the amount of blood volume within the vessels we defined peripheral resistance as that factor that would stop the flow and we talked about four factors that would influence it and we defined peripheral resistance in this section then we talked about cardiac output again as the makeup of your stroke volume times your heart rate per minute so on average we said it's about five liters per minute what influences blood volume we said that could be your nation and voiding or how much we intake