okay last little section or topic that we're going to go over um is how does the body determine which tissues are getting like um well profused with blood lots of blood is going in there and um determine which tissues in this moment anyway are going to get less blood flow so tissues usually get the exact right amount of blood that they need not more and not less if in the moment like for whatever's going on um because we don't have enough blood to like fully peruse all the tissues of the body all the time so the body has to make quote unquote decisions about what tissues are going to get more blood flow and which tissues are going to get less blood flow at any given time again exercise and digestion are the main controlling factors that um that control this so um like I said if all tissues received an equal amount ount of blood all the time blood pressure would fall because there's only a set amount of blood in the body so there's two ways to control this there's intrinsic and ex extrinsic control intrinsic control means that control of how much blood a certain organ is getting comes from within that organ itself extrinsic extrinsic control comes from outside of that organ easy enough right intrinsic control is also called Auto regulation in other in other words the organ is regulating on like by itself it's Auto matically regulating its own blood supply so control comes from within that organ so let's look at that intrinsic control is based on the metabolism of that organ so like if there are okay again it's all everything not everything but many many things go back to cellular respiration let's remember cellular respiration the equation is Oxygen Plus glucose this happens in the mitochondria of cells and this is how we generate ATP which we use to do work okay so we've got this is the summary equation of cellular respiration and if I were to get a little more specific I would ATV I would add numbers so I would say six oxygen sorry about that one glucose give us six carbon dioxide six water molecules and then 36 to 38 ATP all right fine Sor I'm ding like I don't like it um anyway that's cellular respiration right every cell has to do it to get ATP and so therefore every cell needs oxygen and that's why we breathe it in and every cell needs glucose that comes from the food that we eat right glucose either comes from the carbohydrates that we eat broken down into glucose or if we're not eating eating enough carbohydrate we can take protein and convert it into glucose so that we can still get ATP so um every cell needs to do this so great let's say um that in a certain tissue like H we're going to talk about skeletal muscle on the next slide so let's just start talking about that right now let's say skeletal muscle um begins to work a little bit harder like right now I'm sitting in my chair but after I do this I'm thinking about taking my dog for a walk so let's say I do that so I'm going to get up out of this chair and I'm going to start walking so now my skeletal muscle cells need more ATP they need more ATP to walk than they do to sit in this chair make sense they need more energy to produce that movement so in order to make more ATP I need more oxygen and I need more glucose and so the thing that happens in the first like seconds of your activity level increasing is that the skeletal muscle gobbles up the glucose and oxygen that are on hand like that are right there and so all of a sudden because the metabolism the blood flow hasn't picked up yet to match the activity right we just started so there's been no cues to the body yet that the skeletal muscle is gobbling up all the glucose and oxygen and needing more energy so skeletal muscles just using what's on hand and if that's the case then all of a sudden very quickly we will be low in oxygen and so if there is low oxygen or high CO2 or lactic acid but if there's low oxygen because we just gobbled it all up because all of a sudden we're our activity is increasing it stimulates stimulates the endothelial lining of the vessel so the simple squamous epithelium they produce this um molecule called nitric oxide n o a Nitro a nitrogen bound to an oxygen nitric oxide and nitric oxide dilates the capillaries and so when the capillaries dilate more blood flow can come to that skeletal muscle if there's High oxygen or low CO2 so the opposite is happening let me see if I can erase just what I need here like just this part all right so now let's say we were out for a run but then we came home and we were tired and we sat down on the couch right and so we were out for a run so all the capillaries in our skeletal muscle were dilated they were being fed with a lot of blood and so there was a lot of blood on hand so we had a lot we had a lot of oxygen but then we got home and we sat on the couch so for this small Moment In Time there'll be a lot of oxygen in the tissues and if there's more than usual right then um the tissue kind of senses that high oxygen the endothelial sorry endothelial lining releases endothelins and endothelins are a molecule a chemical that's made that causes basoc constriction so then the arterials feeding those capillary beds constrict those capillary beds get less blood flow the just right amount of blood flow to sit on the couch because that that's what I'm doing now all right and so this extra oxygen gets gobbled up and the flow reduces until we have the just right amount of blood coming into muscles that are now sitting on the couch so this is control over how much blood is coming into skeletal muscle based on its use whether it's high or low I think I just described what happens here I did I'm going to leave that same thing happens in the brain there's Auto regulation in the brain so neurons like our brain is just made up of a whole bunch of neurons right and neurons need constant blood supply or they die like um there's nowhere in the brain to store oxygen or store glucose and yet these neurons depend on it and so that the blood supply to the brain has to be continuous and deliver oxygen and glucose continuously all all during the day all during the night of every day so if there are high levels of CO2 or low levels of oxygen meaning something just happened in the brain that stimulated it and it gobbled up a whole bunch of ATP right and so it gobbled up a whole bunch of at it needed a whole bunch of ATP and to make that ATP it gobbled up a whole bunch of oxygen and a whole bunch of glucose and so now all of a sudden it's low in Oxy oxygen if that were to happen then um nitr oxide n o is secreted the vessels dilate and more blood flow to the area occurs and the opposite can happen in the brain as well if that activity slows down endothelins are are secreted the capillaries constrict and the blood flow decreases so Auto regulation is saying that the organ itself is regulating how much blood should be arriving okay by basoc constricting and vasod dilating dilating constricting extrinsic control this is control that's coming from outside of the organ so again we're talking about how much blood does this organ need let's skeletal muscle is an easy example so we'll use it again and there are also controls that are outside of skeletal muscle so uh this is controlled the controls are the nervous system and hormones just like we've been talking about for the whole this whole lecture series um and it's the same idea so hormones and nervous input act on the smooth muscle of the vessels two phase of dilate or phase of constrict um they constrict in areas that need blood flow the least and they dilate in areas that need blood flow the most so that's extrinsic control basically it's coming from the nervous system or hormones that are made somewhere else in the body all right my friends we've made it to the end of this lecture um I hope that it went well for you if you are studying and Rel listening to these things and generating questions please send them my way all right talk to you soon