2.1.5: Feedback

Added: 2026-05-25

[00:00:01]okay this video is all about feedback and positive and negative feedback loops and mechanisms so what we mean by feedback is just a signal within a system that's used to control that system so um something happens and then in response something else happens to help control what's going on that's feedback essentially uh now a feedback loop is when you have the feedback occur a response happen that's considered to be a feedback loop right so with this little diagram here right a happens a causes B to happen B then can have an effect on a that's what we call a feedback loop so this is found in many living and non-living systems it's found in things that are engineered um it's it's found all over the place but it is found like I said in nature um now you can either have positive feedback what positive feedback basically means is that when a happens and causes B to happen B then actually reinforces and increases the amount of whatever a is so it's a positive feedback loop in in that when a happens B causes a to happen even stronger or even more or even faster that's a positive feedback loop now a negative feedback loop does the opposite negative feedback is when something happens with a that causes B to happen and B kind of counteracts or mitigates whatever is happening with a so positive feedback loops help accelerate some sort of change negative feedback loops help um counteract or inhibit change and so negative feedback loops are really important for maintaining homeostasis so like for example right you start to get hot what happens you start to sweat that sweat helps cool you off so you're not as hot anymore that's negative feedback that's homeostasis right maintaining body temperature so we're going to look at some examples here today all right so like I was just talking about actually with uh body temperature that is our first example here then here's a diagram of the negative feedback loops that are happening here right so normal human body temperature right around 98.6 degrees F of course this varies from person to person a little bit you might be a little bit above that might be a little bit below that but if the body's too warm then a variety of things happen right so let's take a look right body temperature rises then a bunch of different things happen blood vessels dilate that helps bring uh blood to the surface of your skin so that it can radiate heat away um sweat glands secrete fluid so you can take advantage of the heat of vaporization of water to draw heat energy out of the skin again um those two things of course are going to help you lose heat to the environment to bring you back to a normal body temperature now with most any of these homeostasis kind of Loops right we're trying to stay to set point so usually there's going to be a a kind of mirrored image like you see here where there's actually two negative feedback loops that work together to keep something at a certain point right because you could also have your temperature get too low right bind temperature could fall in that case blood vessels con strict so the heat is conserved right so your blood stays more in your core if you go outside on a day like today when it's really cold um your your more of your blood's going to stay with your core internal organs and recede from like your fingers and toes and that's why people get frostbite and they can lose like fingers and toes because the blood literally stays back in order to try to keep your uh body temperature up uh sweat glands don't sweat uh and shivering starts to happen so your muscles kind of involuntarily uh activate in order to generate Heat and the whole point of that is to uh bring that body temperature back up right so we have these two Loops right these two feedback loops are both negative feedback loops that help maintain uh that consistent temperature right and so that's an example of negative feedback positive feedback um one classic example of this is blood clotting so again as a reminder positive feedback is where a change happens and then that causes something else to accelerate whatever that change is and so in blood clotting when platelets get activated due to like the release of a wound they actually upon activation release chemicals that activate more platelets so you you cut yourself uh there are chemicals get released um signaling molecules um little hormones essentially that are released from the wound site that attract and activate platelets thrombocytes right or fancy word for platelets those platelets then travel to the site they get activated they start to form a clot and every time a platet gets activated it releases more of those chemicals so those same chemicals are causing additional plate Activation so this is this accelerates the process so you can quickly clot the wound right so you don't wind up keep continuing bleed and bleed and bleed and bleed right we want this to happen quickly and so positive feedback loop like this right this is the loop right here helps us uh clot that wound up quickly another classic example child birth so um pick wherever you want you can start anywhere on this cycle here um but we'll start here right so the head of the baby pushes against the cervix okay so you have the cervix right here when the baby's head pushes against here that causes nerve signals to be sent up to the brain uh of the mother and the Brain then stimulates the pituitary gland to release oxytocin and oxytocin is another hormone so it's a chemical messenger molecule right and that hormone oxytocin actually once in the bloodstream it goes to the uterus and actually causes the uterus to contract so that oxytocin stimulates uterine contractions and of course as the uterus contracts it pushes the baby's head against the cervix and then the cervix sends nerve signals to the brain and then and so on and so forth right and so you keep getting more nerve signals from the cervix more oxytocin in the bloodstream stronger contractions more nerve signals more oxytocin stronger contractions more frequent contractions contractions contractions contractions and eventually get to the point where you know full full-blown labor right and she's pushing and eventually the baby comes out that's another example of positive feedback loop right so you can see how all these things eventually just build on each other right so positive feedback is all about accelerating some change adding to it Whatever It Is NE feedback is all about counteracting or inhibiting changes so what you're going to be doing in your lab Journal although if you wanted to do it digitally and submit it digitally you could do that uh if you want is you're going to research and diagram glucose feedback loops so how does the body maintain normal blood glucose levels right so you're going to need to research the action of both insulin and glucagon we've already talked about insulin you should be pretty familiar with what insulin does insulin is that hormone secreted by the beta cells of the pancreas right that help bring blood sugar levels down right so you're going to look into how that works you should already know we've already covered it right glucagon does the opposite so just like with um body temperature going up or body temperature going down right your blood sugar levels could go up when you eat your blood sugar levels could go down like especially if like you're exercising doing some sort of strenuous activity right um so if there's a drop in blood sugar we need to bring that back up right the cells of the body need to make sure they've got access to that glucose and so you're going to research what glucagon does and so here is kind of an overall map of like how you could do this right so just like with the body temperature one right you got your normal levels and then a change happens right so these little pink arrows here representing a change either blood glucose level rises or blood glucose level drops what happens next so the thing that's going to happen next right is that the pancreas is going to do something and it's the pancreas in both of these situations some other things that are going to be involved in addition to the pancreas so some other terms you should have in your diagram you should include of course insulin and glucon you should talk about the beta cells of the pancreas you should talk about the alpha cells of the pancreas you should also talk about of course glucose but also glycogen glycogen um and glucagon and glycogen look very similar but they are different words they are pronounced differently and they are very different things but they have an impact on each other unfortunately all these words kind of sound the same and that's a little bit tricky right it's because they're all they all do stuff with glucose we got glucose glycogen glucagon different words mean different things uh so when you have this U feedback loop uh in done in your lab Journal make sure you look at the instructions on my pw2 there's a couple other things going to have you add uh it's going to have you like note what goes wrong on like type one versus type two diabetes on your on your diagram come up show that to me uh I'll grade that for you you'll be good to go on to the next thing