[Music] hi and welcome back to three science lessons cold okay by the end of this video you should be able to describe what's meant by the word homeostasis and give examples you should then be able to describe the key features of automatic control systems in the body in previous videos we've seen that cells caveat respiration to release energy from glucose and to do this they use enzymes now a key idea that you need to understand is that enzymes and cells require very stable conditions in order to work what that means is that enzymes themselves cannot work well if the conditions around them change too much so because of this our bodies have systems in place to keep the internal conditions optimum for the cells to function and scientists call this homeostasis I'm surely the definition of homeostasis here homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes now I understand that lots of students find homeostasis a difficult idea but I promise you that homeostasis is easier than it looks just keep in mind that homeostasis is all about keeping internal conditions as constant as possible so the first thing we're going to look at is what is meant by internal conditions I'm showing here an endurance athlete now any sort of exercise places demands on the body for example respiration will use glucose to generate energy and this can cause the blood glucose concentration to fall the athletes body temperature will rise and he'll lose water through sweating so in the human body homeostasis is used to keep the blood glucose concentration the body temperature and water levels constant so essentially homeostasis consists of automatic control systems making sure that the internal conditions of the body stay as constant as possible now in the exam you could be asked to describe the general features of an automatic control system so we're going to look at that now firstly the automatic control systems in the human body can involve the nervous system or hormones and we'll be looking at both of those in later videos I'm showing you the features of an automatic control system here and it's really important that you learn everything in this section this is a very common example topic receptor cells detect changes in the environment now in this case the word environment could mean the body's internal conditions for example the concentration of glucose in the blood however it could also mean the body's external conditions for example the temperature of the skin scientists call a change to the environment is stimulus and again that's a really important word to learn the receptor cells now pass information to a Coordination Center for example the brain the spinal cord or the pancreas the Coordination Center receives and processes the information from the receptor cells the Coordination Center now sends instructions to the effector an effector is a muscle of a gland and the job of the effector is to carry out the response in other words we store the optimum level now over the course of the homeostasis topic we're going to be looking at a range of different systems but in each case you'll see a stimulus a receptor a Coordination Center in effect under response remember you'll find plenty of questions on homeostasis in my vision workbook and you can get that by clicking on the link above [Music]