well when we start learning about physiology we have to learn about homeostasis this is one of the most fundamental principles in physiology homeostasis describes the many mechanisms in the body that keep the environment in the body just right at just the right physiological parameters for the cells to work properly so we don't want it to be too hot we don't want it to be too cold we don't want it to be too wet we don't want it to be too dry we don't want it to be too acid we don't want it to be too alkaline there are many things that must be homeostatically regulated to keep them just right the modern way of describing this is the body needs to be in the goldilock zone the porridge wasn't too hot and the porridge wasn't too cold it's got to be just right for physiology to work many parameters in the body need to be homeostatically regulated now homeo means the same as in homeogene so things are the same so in homeo stasis the homeo part means the same stasis actually means not moving standing still so things need to be kept the same they need to stand still they need to be the same they need to be in the same range in the same narrow parameter so that the physiology works properly so homeostasis literally means something like well literally means same standing standing still and it's a dynamic equilibrium these things are in equilibrium there's not too much and there's not too little but to keep it like that the body's got to be constantly fine-tuning it's a dynamic process process of standing still homeostasis now there's four useful terms when we think about homeostasis and the first is disruptor a disruptor is something that will tend to change a homeostatic parameter so if you go running or it's a hot day you're going to get hotter that's going to tend to disrupt Thermo regulation and temperature homeostasis or if you don't drink for a period of time you're going to get a little bit thirsty and dehydrated or if you're going to drink a lot you might the tendency would to become fluid overloaded you would be getting too much fluid in the body so these things can disrupt the balance and we want the balance to be maintained so there's possible disruptors but then in the body there's things that detect the particular parameter we're considering at the time so there's detectors that detect the disruption and then there's some sort of control system some effectors that bring it back into a homeostatic range so we can think about disruptors detectors control systems and effector systems and all this is necessary because of physiology going on primarily inside the cells so inside the body of course we have Untold billions of cells and in those cells there's biochemical physiological processes going on all the time so let's think about an individual cell now and try and relate that to these principles of homeostasis so here we have a body cell an individual body cell and inside this body cell there's all sorts of biochemistry going on so substance a needs to be converted to substance B that is a biochemical reaction and of course there's many millions of these biochemical reactions going on throughout the body and this is facilitated by an enzyme so in order to have life we need biochemical reactions going on in order to have biochemical reactions going on we need to have the chemicals that are going to take part in the reaction and we also need to have the enzymes and we can start thinking about physiology the physiology of homeostasis in terms of enzymes so for example for enzymes to work the pH needs to be finely regulated the reason for this is that the enzymes are proteins they're complex structures and they have folded arrangements to give them a particular shape and if the pH changes that can alter the nature of the enzymes and if the enzymes are denatured they will stop performing their biochemical function and if the enzymes do not perform their biochemical function that means they will not catalyze the reaction from A to B that means we won't have the biochemistry if we haven't got the biochemistry that means we won't have the physiology if we haven't got the physiology that means we no longer have life so the enzymic environment must be correct in terms of pH and also in terms of temperature the temperature must be right for the enzymes to function enzymes do not like being too hot and enzymes do not like being too cold they must be at just the right temperature and Al also if we're going to have chemistry going on inside the cells we need these things to work remember the PowerHouse of the cell the mitochondria the organel with infolded inner membranes so the mitochondria need to work to generate energy and of course this means in order to generate energy we're going to need nutrients for example we're going to need glucose so we're going to need a certain amount of glucose in the environment around about the cell and the environment around about the cell is primarily the extracellular fluid in this case the fluid around about the cell is the tissue fluid or the intertial fluid the cellular environment needs to contain glucose to provide energy and of course if we're going to have glucose to provide energy the glucose is no good unless we've got the oxygen to combine the glucose with so as well as having the right amount of glucose we don't want too much glucose so we're hyper glycemic we don't want too little glucose so we're hypoglycemic we want just the right amount and we need oxygen as well we need the right amount of oxygen so the oxygen can also diffus into the cell facilitating energy production and of course if we're going to have oxygen then we need the blood supply to deliver the oxygen into the tissue fluid so we need the capillaries with the red blood cells coming along perusing the tissues supplying the oxygen this means we need the right amount of red blood cells we don't want too many red blood cells so the blood is too thick and viscous we don't want not enough red blood cells because that would make the patient anemic and there will be insufficient delivery of oxygen so we need the right amount of red blood cells and of course if we're going to get the red blood cells profusing we're going to to get the red blood cells going through the circulatory system we need the right amount of blood pressure to facilitate the profusion of blood through the tissues so we need the right amount of materials and pressures in the blood to maintain the Integrity of the the homeostasis and integrity of the tissue fluids to maintain the intracellular environment the environment inside the C cell that actually facilitates the biochemical processes that give rise to life and of course as well as glucose we're going to need other nutrients for biochemical processes we're going to need amino acids we're going to need fats we're going to need vitamins and we're also going to need minerals so we're going to need a whole range of nutrients to supply the environment in the cell with all the biochemical substrates with all the chemicals needed to facilitate the biochemistry in the Cell at just the right rate now a lot of cellular activity is controlled by the endocrine system and of course the endocrine system is based on hormones so in the blood and therefore in the tissue fluid we need just the right amount of endocrine hormones many hormones have to be homeostatically regulated at very precise levels we don't want too much of them and we don't want too little of them too much or too little of an endocrine hormone will give rise to an endocrine disorder if we've got just the right amount of endocrine hormones homeostatically regulated to be in a precise physiological range they will control the biochemical activity inside many of the cells of the body in fact virtually all of the cells of the body are subject to some endocrine influences also the cellular environment needs to contain the right amount of water and the right amount of electrolytes such as sodium potassium chloride ions and the other electrolytes need to be present in just the right amount so for example if there's too much water in the extracellular fluid if there's too much water water will tend to diffuse into the cells and blow the cells up conversely if there's not enough water in the extracellular environment if the patient's dehydrated there's not enough water then osmosis will mean that water will tend to diffuse from the cell into the tissue spaces resulting in dehydr ated cells so we need the right amount of water and we need the right amount of electrolytes some cells in the body are described as being excitable cells that is there is an electrical potential difference across their surface membranes nerve cells and muscle cells for example are excitable cells and require just the right amount of electrolytes on both sides of the cell membrane so there can be electrical activity in the nerve cells and in the muscle cells but we need just the right amount not too much and not too little and all the time as this cell works as there's biochemical processes going on inside this cell it's going to produce waste products so there's going to be carbon dioxide produced there's going to be nitrogen containing waste products produced such as ammonia and these are very toxic if these are allowed to build up to toxic levels they will stop the biochemical function inside the cell and indeed they will eventually kill the cell so these need to be got rid of these need to be excreted somehow then need to be got rid of so as well as having many parameters at just the right level we need to get rid of the waste products to maintain the homeostatic environment so everything is in a physiological range inside the cell to promote cellular function well there's just a few examples of parameters that need to be homeostatically regulated in order for the cells to generate this mystical phenomena that we refer to as life