now in a pathway if the action the response hmm put a big ol like big ol red circle around this thing this is my response ooh I don't need an arrow there because that's misleading if the response - at the end of the pathway if the response feeds back and decreases the stimulus that's a negative feedback loop do you see my loop the response goes back to the original stimulus and says slow your roll we're done it removes the stimulus the response makes the stimulus go away if the stimulus is holy hotness in here the response is sweat up a storm and the sweating cools me down so that it isn't so hot in here and the stimulus the hotness has been removed some times now if this step if the response removes the stimulus in a negative feedback loop it is possible if it is a homeostatic pathway that we can maintain homeostasis that way we can sort of if you go out of the range you can negatively feed that back and and get back to the setpoint not all negative feedback loops are homeostatic but if there is a feedback loop if there is a homeostatic pathway there most likely will be negative feedback now I say that and I always love the general statements that I make where it's always this way and it's never true in physio there's always exceptions but I wonder if there are any exceptions to that if there are any homeostatic pathways that don't exhibit negative feedback so if you can think of one holla holla cuz I want to know I can't think of any so we have negative feedback loops that can be homeostatic but not all negative feedback loops are you have jillian's of negative feedback loops that have nothing to do with homeostasis because they have nothing to do with the extracellular fluid awesome you also have positive feedback loops sometimes okay so think about this what's a positive feedback loop dude it's when the response increases the stimulus think about that so the response if a positive feedback loop was happening when I got hot I get hot I start to shiver the shivering the response this would be a bad idea the shivering response actually increases my body temperature so now my body temperature has increased even more which initiates the whole pathway which causes a response more shivering which increases my body temperature even more that's a positive feedback loop the response increases the stimulus in a positive feedback loop most of the time positive feedback loops are bad news like they're not there you're gonna die if my shivering increased my body temperature and then increased body temperature caused shivering I mean that's like that's crazy and I'm gonna die which is why we don't have critters that have strategies like back they all died there are some positive feedback loops though in your system and you didn't die thankfully I've done it twice birth holy positive feedback loop the process of giving birth you actually I mean it's insane so thank your mother for going through that process for you because that's how you got here the uterine contractions push down on the little human that's in your belly so that the little humans head like smashes into your cervix which is the opening at the base of your uterus that's how you get out of your very first apartment and your mama's uterus and the pressure on the cervix causes stretching in the cervix which is a stimulus which has a response of increasing uterine contractions brilliant which causes increased stretching which increases contraction which increase the stretching which increases contraction which is how you end up like what pushing a giant thing out of you and it comes out eventually so there is a cutoff point to the positive feedback loop because you get it out and at that point once you get it out then you're golden then you're like the whole system stops you the stimulus has gone away because it came out thank goodness birth thank you for positive feedback loops blood clotting is another example of a positive feedback loop where the chemicals in the blood that actually caused the clot to form initiate additional production of chemicals that cause the blood to clot which initiates additional chemical production that causes the blood to clot and you can imagine that that would be a total disaster if that one got out of control thankfully we have strategies in the blood vessels that prevent that like crazy like peace out blood clotting forever cuz that'd be terrible okay so we're gonna mess today in lab we're going to have pathways like the whole day is pathway fun times fun times I say and so you're going to get lots of practice with this concept here you get lots of practice with this concept for the rest of the semester and now I'm out of here oh boy