welcome to this short lecture on cell adaptation in this particular lecture we're going to look at how cells respond to stress is placed upon to keep you alive so when your cells are confronted with stresses placed upon them which will impact their structure and their function cells need to respond to this particular these stresses to essentially keep the cell alive now this particular diagram here is a schematic drop diagram to show you how cells constantly exposed to different environments and how cells need to respond to keep homeostasis going and to keep the cells the tissue and ultimately you alive so here we've got a picture here got a diagram of a normal cell so this cell is trying to keep its homeostasis but what we can see is there's some arrows pointing down to cell injury and over here would be stress as a place of placed upon the cell so if certain stresses on the cell such as work load or demands on the cell hormones a change in pH a change in nutrition exposure to chemicals or irritants or inflammation the cell needs to adapt to this particular environment and if it can adapt it will ultimately go back to its normal homeostatic State similarly the cell can be also exposed to very potentially very harmful things such as mechanical trauma chemical trauma physical trauma a drop in a reduction in oxygen and this is going to lead to the cell to become injured now the cell what needs to recover after injury and it can do this through ways of wound repair or regeneration such as resolution regeneration replication in some times it needs to replace the cell type and the is what we call a reversible injury so this can reverse and go back to the normal cell homeostasis but if a cell can't deal with the injury that's placed upon it it will essentially go into an irreversible state and the cell will die now mike has done this in a video and this is known two types of cell death is known as necrosis and apoptosis so Mike has done that video so we're not going to focus too much on that what we're really going to focus on is how the cell adapts to stressors pace that placed upon it so this the cells can usually go through four or five main types of adaptation these are known as atrophy hypertrophy hyperplasia metaplasia and displays you now the first three I've drawn on the board we've got atrophy here we've got hypertrophy and we've got hyperplasia now I'm going to do that in a second but there's a few points just to be aware of firstly when you think about all the cells in your body they are generally categorized into three three ways in how they're constant activity is essentially situated so some cells are what we call labile cells which are constantly replicating and copying themselves this is going through mitosis so they're very mitotically active then you have a group of Quinn essence cells or stable cells so these are cells almost asleep so they aren't copying themselves aren't replicating themselves but they can if need be and then finally we have permanent cells which are cells that will never go through mitosis again they can never replicate they can't ever copy themselves or go through mitosis to repair themselves examples of these type of cells would be muscle cells or neuronal cells okay so that's important to be aware of because that will dictate the way that adaptation progresses so essentially before we get it to adaptation I just want you to really understand this diagram that a normal cell when it's based upon when stresses are placed upon it the cell needs to adapt to these stresses to keep the cell alive okay some of the some of the exposures could be very injurious agents so that could be say a reduction in oxygen or some can be just to increase in demand so imagine this cell is a muscle cell in your heart if you're if you have a restriction in blood flow to the heart such as angina or potentially a myocardial infarction the cell isn't getting any oxygen anymore so it needs to respond to that injury hopefully it can rectify by getting oxygen back to it but if it doesn't get the option it will essentially go into irreversible state and die now if it get in if it gets injured a little bit the muscle can repair itself but it generally would change its state and become more scar tissue more collagen so this is a replacement in cell so it's reversible but it may not be functionally that great but another example of in the muscle in the heart muscle cell would be if you put a lot of stress on it either through hypertension high blood pressure or you work it hard to exercise the the stress placed upon the heart muscle is the demand and so it has to respond to that and because it's not a labile cell instead of getting increase in number all it can do is get bigger and that's called hypertrophy and so now we're going to do this adaptation at least for the first case with the these three types let's start over here with atrophy so atrophy what you can see atrophy is a cement basically means a reduction in size so here we can see four normal sized cells sitting on a basement membrane with a nice blue Nickolas now going down here what we can see these four cells have reduced in size so this is known as atrophy so basically what's cool in the a trophy is a reduction in work demands or possible stimulation through hormones or growth factors now the reason why it would decrease in size is it would make the cell more efficient so if your cells weren't being used so this is a good example of why you why cells would become atrophied is disuse for example if you were to break your arm and you were to put your arm in a cast you're not now moving your hand and fingers and so forth so the muscles in your forearm aren't being used anymore so when you take that cast off in eight weeks your muscles in your forearm have become smaller which is atrophy now the reasons why it's doing that well it doesn't need it doesn't have a demand placed upon it so the cells basically reduce their size which makes the cells more oxygen and energy efficient and it's better in the long run for everything so that's an example other examples of atrophy could be denervation so the nerve go into the muscles could be cut and that would cause atrophy a reduction in nutrition a reduction in hormonal stimulation a reduction in blood flow so the way that atrophy can be categorized is in two ways either physiological atrophy which is a normal response to a stimulus or a pathophysiological response which is added more disease like an example of a physiological atrophy would be lets say the muscles in the uterus after pregnancy so during pregnancy all the hormones that has caused the uterus to get bigger to grow with the developing fetus once the fetus has passed out the hormone levels drop so that means the uterus drops back to its original size and that's at refine now it's important to note that atrophy is a decrease in cell size not in number so these are usually in stable cells or permanent cells such as muscle cells another example of what let's go to a path logical example a good example pathophysiological example of atrophy would be ischemia so ischemia so this is a reduction in blood flow so if you were to have let's say peripheral vascular disease so this is a reduction in blood vessel diameter into your legs the your muscles in your legs would actually act rifai because it's not getting enough adequate blood supply so that's an example of a a pathophysiological cause another example would be d innovation so if you let's say the muscles to your forearm if you had a median nerve cut so if your meeting there was cutting your arm that means the nerve signals go into your muscles in your forearm being reduced or actually completely stopped so that means all the neurotransmitters that go to the muscle which are like growth factors aren't there anymore and the muscles in the forearm will actually get smaller that's an example of atrophy so I think that will do for this particular one moving across to hypertrophy so what we can see here these four cells in a normal state but comparing it to these four these four are much bigger again like in atrophy we're talking about still cells that are permanent so a good way to remember the hypertrophy are in muscle cells in the body so this could be skeletal muscles and cardiac muscle cells so usually the stimulus for hypertrophy to to become apparent is usually in response to mechanical force or stretch placed upon it such as muscle contraction hormonal stimulation or growth factor stimulation so a good first example is getting bigger by going to the gym so if you were to go to the gym and lift weights what you're doing is you're placing mechanical stress on the muscles lifting the weights such as doing dumbbell curls so the biceps have been the demands placed on your biceps this is the stressor is increased so the muscles respond to this by increasing the genes or the gene expression to make more proteins for contraction and also organelles will be increased as well such as mitochondria because you need more energy etc another example of a physiological response is the uterus in pregnancy so in this case it's going to be a hormonal stimulation not so much a mechanical force so the hormones are going to get into the uterus smooth muscles of the uterus and tell the uterus to get bigger and more powerful so when it comes to the point where we need to push that baby out you have a much more greater amount of muscle tissue to do that particular act another example which could be a combination of physiological and pathophysiology could be the bladder so if the bladder was had a restricted flow such as in a prostate an enlarged prostate so when the blood is trying to empty and push the urine out it's got a restricted flow so that the bladder needs to get increased strength and the way it does that is also build up its muscle content within the wall of the bladder and this would probably occur through a similar example of the gym where you place increase force and demand on it some examples for a pathophysiological so a more diseased State hypertrophy would be in the heart so this would be cardiac myopathies so you could have an increased heart muscle size in athletes so this is a good thing and so what what they proposed here would be as the muscle gets bigger proportionally the length and the width increases proportionally so as the muscle of the heart actually gets bigger and bigger it continues to be efficient but in some of the myelopathy cases such as dilated correct Bob Athey what happens is the muscle gets bigger but it gets longer in length proportional to the width and that at some state the heart becomes inefficient and ineffective and there becomes a problem with contraction another example of a marbeth E is hypertrophied correct mapa the-- where you get a a unfortunaly portion or width versus length so the muscle becomes in the heart becomes really bulky but then it restricts the ability of the heart to pump or fill and this becomes a disease example so these are important to note that hypertrophic like atrophy can be physiological but also pathophysiological but it's important to note that these two cell types are usually permanent cell types such as muscle okay and the way that overcomes the demands placed upon it is that increase in their case increases the size of the tissue by increases the size of the cell whereas if we go across to here so this was called coming across to here this one is high play zero okay now if you were looking at the actual tissue level in either case here the tissue size would increase but the difference is the tissue size increases with hypertrophy by the increase in size but in this one the increase in organ size is actually through increased cell number so hyperplasia is increase in cell number not cell size so the cell type in hyperplasia is actually labile cells or and labile or stable cells so that not in permanent cells so examples would be epithelial cells hemopoietic stem cells or in the bone marrow liver cells glandular cells intestinal cells so in this case there's stress placed upon it sim to here but the way that the cells respond these label or stable cells is to increase the number okay again like the other two there's two categories of hyperplasia there's physiological which is normal or pathophysiological which is disease like some examples of physiological then the inducing agent would be a hormone changes in hormone so a good example would be hyperplasia of the breast breast tissue both going through puberty for the female or going through pregnancy for the female so the change in hormone concentration will cause breast tissue to increase its number of in number such as ductal cells to increase the ability to produce milk a good example of a change in the stable cell would be in the liver so the liver is composed of her parasites the hepatocytes are usually dormant or quiescent so the color asleep but if you were to cut the liver in half and remove that liver that half the liver out what would happen is the parasites would become activated so the genes that get turned on for hyperplasia are genes for the cell cycle and like for hypertrophy which are genes to produce organelles and genes to produce muscle proteins for contraction so these are genes for cell cycle so you now turn on the cell cycle and you increase mitosis so you start replicating and replicating so it's important to note that this has to happen in the label or stable cells at least so we've done the physiological examples that we've done breast tissue and liver cells also another example of physiological if you're a mountain climber or if you're an athlete and you're constantly exposed to hypoxia through activity and exercise your hematopoietic stem cells in your bone marrow would produce more and more red blood cells so that's hyper plays Union bone marrow to push red blood cells out to increase the oxygen care capability now going to a pathological cause of hyperplasia a good example would be the prostate gland so it's exposed to levels of androgen hormones and that causes the prostate gland to increase in size so this is very common for males over the age of 50 so the prostate increases its size through hyperplasia and that's in response to hormones or in this case androgens another good example of hyperplasia in a pathophysiological context would be if you're exposed to a particular virus such as a papilloma virus this causes as a result warts so we have an increased in growth or hyperplasia in the skin where you get these little bumps which are known as warts that's caused by a virus not in the case of a physiological cause that would be considered pathological so that's the atrophy hypertrophy and hyperplasia so what I'll do now is I'll go to the last two so I'll rub this out and the last two known as metaplasia okay and displays you so with metaplasia what ultimately happened happening here is we're changing in the cell type or the morphology so the way that the cell looks it will it will change its type now this is usually in response to chronic irritation or inflammation so when the environment of the cells are exposed chronically so long-term - inflammation or a type of chemical irritation the cells think they think well form for us to survive we need to change and equip that equipped ourselves to be more like a different type of cell to survive so this is an adaptation which is not changing the number but actually the the way it orientates itself to be more likely to survive so if it was six if it was exposed to if these cells were exposed to say a lower ph like an acidic environment it would want to produce cells that are more like the stomach because the stomach has cells that are very good to survive a pH a low pH or if you're exposed to chemicals like in cigarette smoking instead of cells that have the cilia that are important to push stuck you know particles in it with mucus out for a particular protective purpose the the chemicals in the smoke the best type of cell to respond to that would be a stratified it cell so if we think about if imagine this is a slated cell so it's got cilia on it okay so this is in your bronchioles now if you expose these cells to chemicals in cigarette smoking instead of being isolated isolated pseudostratified cell it's going to become stratified squamous cells so they'll become cells that will be many layers in thickness okay so it responds in this way because it feels that this cell type is better when exposed to chemicals in the cigarette so it can seem to respond and depth better in this state rather than this date when it's responding to this particular chemical environment it's important to note that in metaplasia it is actually reversible so this is met metaplasia and it is irreversible once you remove that stimulus away in this case it's going to be the cigarette smoke now the other example would be in gourd so gastroesophageal reflux disease so in this case we're starting off with cells which are stratified squamous cells in the esophagus but as the stomach acid comes out of the stomach up into the esophagus and these cells are exposed to acid the cells actually respond by becoming more columnar like so more long like this and the reason why it does that is because they're the cell types in the stomach and it seems that this cell type does better when exposed to acid so the take-home message with metaplasia is the genes that are activated are genes for differentiation so the cells have to be not only a labile cell but they have to be a stem cell so a partially undifferentiated cell so they can change their morphology to suit the the change in environment okay so that's important to know but it's also important to note that the cell the the stem cell can't change to a completely different cell so you can't go from an epithelial cell to a connective tissue cell or a muscle so or a neuron cell you can you can only be an epithelial cell but the epithelial cell can change in its appearance from a stratified cell to a columnar or or cuboidal cell or a columnar back to a stratified okay so that's metaplasia finally we go to dysplasia okay so this is dysplasia which means disordered growth and in this case what really happens is again the stimulus is going to be chronic irritation or inflammation but unlike metaplasia the response to this particular change in the environment is a deranged growth so not only do we increase the the number of cells okay so we increase the number but we might increase the shape so we might have flat ones round ones cuboidal ones squamous ones and it's going to be all disordered so have hyperplasia so we have an increase in number but we also have an increase in shape in the way that it's organized so this is dysplasia so the response from the normal tissue to this plastic tissue is both an increase in cell number and increase in cell size or decrease in cell size and way it's organized so it's very disordered now this is usually considered a precursor for cancer so a good example would be in the cervix so if imagine this is cervical tissue well in survival survival tissue is normal normally stratified tissue okay so imagine that's stratified squamous tissue now in this case it's exposed to a virus again the papilloma virus after the exposure to the environment it goes through a dysplastic growth which makes it much disordered and this is pushing it towards a precancerous State so if you were to do a pap smear on the cervix you would see that dysplastic growth which is different to how it normally should look and this is usually indication we're going towards a precancerous state that is dysplasia and that's why you're given females are given the HPV vaccine so the human papillomavirus vaccine to stop that dysplastic change another example is in the bronchioles for preterm infants so if an infant is born but prematurely before 30 weeks naturally for the the baby to survive it will need to be ventilated and given oxygen etc that exposure causes a dysplasia so this is called bronchopulmonary dysplasia and approximately 20 to the 30% of infants born but before 30 weeks will develop that kind of this dysplasia now finally unlike metaplasia this can be reversible but it's less likely so this is really something to be aware of because this is usually the precursor or the first stage of like a cancerous state so hopefully now you've seen the different types of sellable app tation so we can see a normal cell and when it's exposed to changes environments like workload demand hormones inflammation chemicals growth factors it adapts it can adapt through getting smaller getting bigger increasing the number of cells the morphology of the cells and that that's totally dictated by the cell type on how it essentially changes but that that adaptation is essentially to keep the normal cell alive and hopefully now you can understand why they do it and how they do it