Homeostasis

hi everybody dr mike here i think it's time i'll let you in on a little secret every single day the environment is trying to kill you whether that be extreme changes in temperature or the availability of nutrients or little microbes infecting you via cuts or scrapes in your skin that environment is trying to kill you luckily for us we have a body that can respond to these changes in the environment to make sure that we maintain a stable internal environment and it's this response that the body has to these drastic changes in the environment that

we term homeostasis now homeostasis means similar balance now what does that mean well i want you to think about this pick any function of the body it could be blood pressure it could be blood glucose management ph balance it could be carbon dioxide levels it could be temperature regulation doesn't matter pick any physiological function and you'll find that they all have this happy healthy range that they like to work within so let me just quickly draw that up there's always a range in which there's upper bounds and lower bounds upper boundaries lower boundaries and it

needs to stay within this in order for you to be happy and healthy if it goes a little bit too high above the upper bounds then you don't just get unhappy but you get sick and likewise if it goes too low you don't just get unhappy you get sick as well homeostasis is the body trying to maintain this happy healthy balance of its physiological range now some ranges can be quite wide like blood pressure it has higher boundaries and lower boundaries that are quite wide but some are quite narrow like blood ph and temperature regulation

but regardless the homeo in homeostasis is referring to the fact that there is a range you can sit within if there was a single value like let's just say for core temperature regulating your core temperature and you know that that's at around about 37 degrees celsius right it's not just one value that you need to maintain it's not just 37 degrees and you can't go either side of that if that was the case it would be called homostasis but it's homeostasis and you can go up by around about 0.5 degrees and you can go down

by around about 0.5 degrees celsius before you start to notice ill effects or again you start to get sick so let's talk about homeostasis because it is the most important concept in anatomy physiology and medicine really is and you need to understand it so when you open up a textbook and you look at homeostasis you'll find that regardless of the physiological function you're referring to there's always the same components that keep coming up right and some textbooks say there's three components of homeostasis some say there's five some say there's six we're going to go through

all of them because they're all important let's take the example of trying to regulate our internal body temperature and like i said to you before it's around about 37 degrees the internal core body temperature and you can go up by around about 0.5 degrees celsius and down by around about 0.5 degrees celsius and that is your happy healthy range but let's just say you decide to spend the day out in the sun now we know that the sun is hot and the sun is going to increase or try to increase your body temperature this is

what we call the stimulus so there is always a stimulus when we talk about homeostasis that is the first part the first component of homeostasis what is stimulus stimulus is the change in the environment that's homies oh that's the stimulus that's the change in the environment all right here the temperature is going up increased temperature now your body can't respond to these changes in the environment these stimuli for plural unless you have something that can pick it up and measure it so this is a receptor so the second aspect is that the stimulus must get

picked up by a receptor and this is a super important concept because without a receptor you cannot pick up the change in the environment now there are some things like uv light that we don't have receptors for we have receptors for pretty much everything right temperature uh mechanical pressure uh even just pre other types of pressure in the environment chemicals all these different types of receptors right there's so many different types but we don't have receptors for uv light and therefore it's really hard to detect when our skin is getting burnt by uv light and

damage so our body can't respond so we go from playing in the sun to getting a skin burn right but here we're talking about temperature and the temperature goes up that's the stimulus the receptor that picks this up is going to be a thermoreceptor thermo meaning temperature so the receptor picks up the change it picks up the change which is the stimulus now i said there's different types of receptors temperature receptors pressure receptors mechanical receptors chemical receptors and so forth what needs to happen is the receptor needs to what we call transduce it needs to

turn that stimulus whatever it may be into an electrical chemical a signal so the receptor picks up the change transduces it and then needs to send it somewhere and it sends it either via nerves or through generally the endocrine system so either through the nervous system or endocrine system and where's it sending it to well it's sending it to the third part of homeostasis which is the control center so there's always going to be a part of the body that takes the information sent by the receptor and decides what we need to do with it

all right now remember the stimulus here is an increase in temperature that's the stimulus the receptor picked it up sent it to the control center and the control center decides what's going on well the temperature's gone up uh it's going above that 37 degrees that's not where i want to go so i need to bring it back down what can i do to bring the temperature back down i know i can send a signal to the sweat glands in my skin to sweat and if sweat then accumulates on the surface of my skin when a

breeze goes past through the process of convection it can take that sweat and heat away from the body cooling us down that's what the control center decided to do so it goes all right in order to do that i need to send the signal to sweat glands and that's what the control center does it's decided what it needs to do and it sent it off to the place or the area that makes the change and this is what we call the effector the effector has the effect it makes the effect so the control center decides

what needs to be done it's the area that decides sends it to the effector and in this case the effector of sweat glands but depending on the situation or the physiological function we're referring to the effector it can be cells glands muscles right can be a whole range of things but in this case it's sweat glands now what was the effect the effect was to sweat and what did this end up doing right what did this end up doing let's have a look the effector allowing us to sweat resulted in a drop in temperature which

is the opposite of the stimulus but that's what we wanted right when it went too high we brought it back down it brought it back down so it did the opposite of the stimulus it negated the stimulus it's negative feedback and this is what we call negative feedback this is one type of homeostasis which is negative feedback really really important the most common type of homeostasis to try and bring things back so what does the effector do it negates the stimulus and so you can see here we've got four important parts of homeostasis but i

said there can be six so what are the other two that we need to add in here well when the receptor sends the signal to the control center it sends it like i said through either the nervous system or the endocrine system generally this is what we call an afferent signal afferent when the control center has decided what it wants to do and needs to send it out to the effector this is called an efferent signal now the way you remember f efferent goes to the effector right it's moving away from the control center afferents

going towards the control center so these are two additional aspects of homeostasis the afferent and the efferent signals going to the control center and away from the control center now we didn't say what the control center was here in temperature regulation it's the brain specifically it's a part of the brain called the hypothalamus that can deal with temperature control and sends that signal out and again negative feedback now you can look at this and think about what happens in the opposing scenario what if it's not a sunny day right what if it is a cold

day now this is me trying to draw a snowflake which is a not the easiest thing for me to do and i suppose a snowflake how many sides does a snowflake have it's a good question and i'm not sure anyway it's cold so the temperature drops so you're now going below that 37 degrees and down here to where you're starting to get unhappy unwell that's the stimulus drop in temperature receptor still a thermoreceptor picks up the change sends it via an afferent signal to the control center and it says what do i need to do

well it's cold i need to bring the temperature up how can i do this i can shiver i can contract and relax contract and relax my muscles that's what shivering does why because when you contract relax contract relax muscles it generates heat wow that's perfect the effector here are the muscles now and what it did was increase temperature that's still negative feedback because have a look the effector negated or did the opposite of the stimulus so it's still negative feedback so that's perfect now the last example i want to talk about is positive feedback so

positive feedback is a tricky one there's not a huge amount of examples but there are some that we can refer to and probably the most important is that of the process of labor giving birth now all these things are the same there's still these components so if we start at the stimulus think about this it's time for mum to deliver the baby now that baby is sitting in the uterus and needs to move past the cervix now as this is happening right as the baby starts to move through that big old noggin that the baby

has starts to stretch the cervix okay the stimulus is stretch it's stretching the cervix this is picked up by receptors in the cervix itself it sends an afferent signal to the control center again the hypothalamus and the hypothalamus goes oh what's going on here the cervix is stretching because bub wants to come out what do i do here i know i need to help bub come out so i'm going to release a chemical that tells the uterus that the bulb sitting in to contract and if it contracts it helps to push bub out so the

hypothalamus says all right i'm going to release oxytocin oxytocin is a hormone this hormone is in the posterior pituitary gland it gets released moves through the blood the bloodstream by the so that's the efferent signal and it goes to the muscles of the uterus and what does the uterus do the uterus contracts now when the uterus contracts it pushes bob what do you think that means bob's head starts to push even harder on the cervix and continues to stretch so the stimulus here is stretch what do you think the outcome the outcome increases the stretch

so in negative feedback it would have done the opposite but here in positive feedback the effector the outcome exacerbates it amplifies it reinforces the stimulus and this is positive feedback now you might be thinking well what's the outcome here well this whole thing continues because the uterus contracted to push bub's head against the cervix and it further stretched further stimulated further released oxytocin more uterine contractions more stretching this whole thing happens until bubs out then when bub's out there's no more stimulus and the whole thing stops and that's a perfect example of positive feedback so

what have we learnt today that homeostasis is the body trying to maintain some internal balance internal stability doesn't want to go outside the upper and lower limits but there's a range that it sits within which is different for all functions but if it does go too high or too low the body wants to respond to try and bring it back into its appropriate range and to do that it can use negative feedback for example and all the same components happen work within homeostasis regardless of negative or positive feedback they are the stimulus the receptor the

afferent signal the control center the efferent signal and the effector in negative feedback the outcome of the effector is to negate or do the opposite of the stimulus in positive feedback the outcome is to exacerbate or amplify the stimulus hi everyone dr mike here if you like our videos please hit subscribe and leave a comment