good morning bio 181 I've received a lot of questions about the difference between negative and positive feedback loops so I thought I'd record a little supplementary lecture to help you guys understand it a little bit better so basically both of these types of feedback loops involve some sort of stimulus in the case of negative feedback loops that stimulus is a departure from the set point in the case of positive feedback loops there's not really a set point per se but there's a starting stimulus that sets off the positive feedback loop now in a negative feedback loop you have your departure from the set point your sensor detects that it sends a signal to the effectors which trigger a response which then brings the conditions in the body back to the set point and so that's that's the idea that's what makes it negative you're diverging from the set point and then the response brings it back to the set points you're going in the opposite direction from the stimulus the contrast is in a positive feedback loop you have some sort of stimulus that stimulus triggers a sensor which triggers the effector which causes a response that actually increases the direction of the stimulus so it basically ramps up that response and it becomes much stronger and much more proud so instead of returning to the previous condition it actually amplifies whatever thing is happening so that's the major difference between a negative feedback loop and a positive feedback loop let's take a look at some examples to kind of help you understand this a little bit better so for the negative feedback loop we can look at sugar in the blood all right so when you eat food that's going to increase your blood sugar levels that's not good for your body your body needs just keep relative you need to maintain homeostasis of that blood sugar keep a relatively constant blood sugar so that it's delivering the right amount of energy to all the cells in your body so when you eat food that increases that blood sugar level there are cells in your pancreas that detect that increase they then secrete insulin which is a hormone which triggers the liver to uptake glucose and store it as glycogen that brings that blood glucose level back down to the normal range and you return to homeostasis so your blood sugar level goes up when you eat but then your pancreas reacts to that to bring it back down to a normal level so it's a negative feedback cycle negative feedback cycles are much more common in the body and positive feedback cycles and negative feedback cycles are involved in maintaining homeostasis of any variety of different systems in the body all right positive feedback in contrast an example of that is childbirth so initially you have an initial stimulus it's probably usually going to be at the stimulus is going to be the pressure of a full-grown baby's head against the cervix the the cervix that actually will transmit signals to the brain and the brain the hypothalamus in particular is going to stimulate the pituitary gland and then the pituitary gland is going to secrete oxytocin and then oxytocin is going to go back to the uterus which is going to stimulate contractions of the uterine wall that those contractions will then push the head of the baby harder against the cervix which sends another signal back to the brain which then sends more signals down to the pituitary to release more oxytocin which causes more contractions which causes more pressure on the cervix which causes more signal to the brain which causes more oxytocin and it goes round and round around and escalates and escalates and escalates until the baby is born once the baby is born then there's no longer that pressure on the cervix and the cycle stops so in that case it's a positive feedback because the signal is actually triggering a response that causes more of the signal which causes more of a response so hopefully that cleared things up on the difference between negative and positive feedback if you have any questions please hit me up in the discussion board and I hope you're all are doing well this morning