[Music] hi it's Mr anderson and today I'm going to go a little bit uh deeper into feedback loops and talk about the elements of a feedback loop you hopefully know the difference between negative and positive feedback loops and you could list a few like thermo regulation blood glucose we'll add blood calcium as we go throughout the year and there's a number of feedback loops that control both inside of us and the outside of us uh but I want to talk about the elements the important elements of a feedback loop so you're comfortable with them and so if we think of us as a system we're constantly getting input and we're constantly giving output output but that's not a feedback loop a feedback loop doesn't really exist until we take that output and that actually feedbacks into the system and so until we have a loop then we really don't have a feedback loop so what we're looking for are loops now the terms should also be familiar with in Other words you should understand what a receptor is and what an aector is what a stimulus is and what a response is and if you've looked at any of the feedback loops in our book you'll start to realize that they have a similar pattern in other words the receptor is always going to be in the middle and then you're going to kind of have a figure eight like this so we're going to have a figure eight what happens if it goes up too high what happens if it goes too low and so the receptor will always sit in the middle and then the aector is going to sit at the top and the other aector is going to sit at the bottom and so if we look at these definitions receptor and aector they're organs and so those are things physical things so the receptors are and the aectors are going to be at the top and the bottom of this figure eight and then these are actions and so the stimulus and the response and the stimulus and the response so put some arrows like this those are going to be actions on either side in other words what it does or what it sends or what it what it's doing and so those are the elements of the feedback loop and so not only should you know negative positive but you should be able to say what's the receptor what's the aector what's it doing what's it how's it working and so let's try that with a little bit of practice and so the example I gave you as far as feedback loops go is one of these speed signs and so when you see a speed sign then you if you're going too fast you may slow down and if you're going too slow you may speed up and so let's define some of the uh receptor and and the aector and so let's do our little let me get a color here and so I'm going to put a receptor in the middle now I could do a couple of feedback loops but let's just deal with the person and so what's the uh receptor let's say the receptor is going to be your eye it's going to be in the middle what is an aector let's say a foot up at the top and let's say your foot down here below so if I say those are the organs so we're going to put an eye a foot and a foot at the bottom so this is going to be my receptor and this is going to be my aector on either side and so if if if we talk about specifically what the stimulus is well let's say the stimulus is that you're going I don't know we'll say 38 miles an hour what's going to be your response your response is going to be slow down let's say that you're all of a sudden going 22 miles an hour so that's going to be the stimulus what's going to be the response you're going to speed up and so that'll feed back to the eye and so what we're going to have is this feedback loop that's constantly going up here and then down here and then up here but it's kind of keeping you close to that that set point of that speed that we that we want it to be and so we have a negative feedback negative feedback and it's kind of keeping you in that that little uh center point the example that your book constantly talks about or all science books talk about is a thermostat and it's a great example and so if we talk about how a thermostat keeps a room warm well the thermostat so what are the the what are the nouns what are the organs in this case the thermostat is going to be the receptor so we're going to put that right in the middle we're gonna have a furnace which is going to be an aector and then we'd have another furnace up here so let's say that the temperature goes too high so if the temperature goes too high what is the furnace going to do furnace is going to turn off let's say the temperature goes too low so that's an action or our stimulus what's our response going to be then it's going to turn on and so those are just analogies ways that you can understand how a feedback loop works but remember we're going to put the receptors and the aector at the top at the bottom and then right in the middle and so that keeps us close to a a set point now let's try to do some real ones in biology so let's try and do thermmore regulation so thermmore regulation so we've got rid of their definitions over here so we're going to put the receptor in the middle so the receptor in this case is called the hypothalamus hypothalamus is going to be an organ it's actually a it's a little bottom part of the brain that drips down from the brain um lower portion of the brain it's connected to the pituitary um but the hypothalamus is going to sense your temperature so it's an organ and so let's start with a receptor right here in the middle and you may want to start with temperature okay so let's say that we get too hot so let's say that our stimulus is that the hypothalamus is getting too hot what are someectors that we could put at the top well one example would be like sweat glands uh what's another one capillaries like that my handwriting is not great so well let's say the temperature goes too high our organs at the top could be sweat glands capillaries so if it goes too hot what are the sweat glands going to do what's their response well they're going to sweat and that through evaporative cooling is going to lower our temperature what are the capillaries going to do if they get too hot then they're going to dilate so there's more blood going by the surface of your body and so that's going to release more heat and so that's going to lower our temperature as well and so our response is going to depend on what the aector is let's say that our temperature goes too low what are some things that could act down here well capillaries again so if capillaries before were dilating when we get too cold then they're going to constrict and so what that's going to do is hold more of your temperature close to the body uh what's another one your muscles for example our muscles could eventually start to shiver and that's going to generate a little bit of heat um we could have goosebumps where it holds our hair up on end which doesn't really do much if you don't have a lot of hair it's not like a dog but it does kind of pull your skin in tight like a coat pulling in tight it's going to hold more of that heat and so this is our characteristic feedback loop where if it goes too high we do these things if it goes too low we do these things and so that keeps our body temperature near that set point right in the middle another example is uh is blood glucose so blood glucose if we think about that we should maybe set up the organs first and so what would the organ be in the middle well the organ is going to be the pancreas so the pancreas let's put that right in the middle what are we going to have if our blood glucose goes too um too high well the remember the way I always do it is that we've got beta cells at the top and alpha cells at the bottom now what are those well inside the pancreas if we say the pancreas looks it doesn't look anything like that but the beta cells are going to be speckled over the surface of the pancreas they're parts of what are called the eyelets of Langangerhans and then we're going to have alpha cells as well speckled around here so they're sensing the blood glucose level if the blood glucose level goes too high uh then what is our response well the beta cells are going to secrete insulin and so what does the insulin do insulin is going to hit insulin receptors on your cells it's going to open up these glucose transports and glucose is going to start coming into the cell uh let's say it goes too low so if it goes too low so this would be our our uh our stimulus what's going to happen we're going to release something called glucagon and what glucagon is going to do is it's going to um trigger the liver to break down glycogen into glucose and then release that into the into the cells and so um we got this great feedback loop which is going to keep our our blood glucose levels about perfect why is it important that we keep our blood glucose levels perfect it's because glucose is the fuel and if we can't get that fuel to ourselves or if we use too much of it too quickly then we're then we're out of out of luck and so the whole thing is built on this feedback loop where we constantly are keeping ourselves close to that set point as far as blood glucose goes but remember the whole thing let's find a different color is tied around these organs in the middle so the receptors and the aectors and then the stimulus and the response and so when you ever see one of these figure8 diagrams in a book or anywhere always be thinking back to the to the wonderful elements of a uh a feedback loop nouns actions organs actions and I hope that's helpful