Lesson video

This lesson is called "The importance of maintaining constant conditions in the body, including osmosis," and is from the unit "Coordination and control: maintaining a constant internal environment." Hi there, my name's Mrs. McCready, and I'm here to guide you through today's lesson, so thank you very much for joining me today.

In our lesson today, we're going to explain why it is important for living organisms to maintain a constant internal environment.

And we're gonna have a look at a good number of scenarios to see why that is the case.

Now, in our lesson today, we're gonna come across a good number of keywords, and they're listed up here on the screen for you now.

You may wish to pause the video to make a note of them, but I will introduce them to you as we come across them.

Now, in our lesson today, we're going to first of all look at the effects of changing internal temperature before we have a look at the effects of changing internal water content before we consider how the body maintains these constant conditions.

So, are you ready to go? I certainly am.

Let's get started.

Now, just by looking at the outside of our body, we can see that it is complex and it has a complex combination of many different specialised cells that work together to make us survive and thrive.

If we look even further inside our body, we can see that there is an even greater number of specialised cells.

And each of those specialised cells has a special set of chemical processes within the cells making up the tissues and the organs, and all of those things work together to enable us to survive, to be healthy, and to thrive.

Now, every chemical and structure within our body has a distinct role to play in keeping us healthy, and all of them must work together as effectively as possible to keep us alive and in good health.

Now, enzymes are a fundamental part of that process because almost all cellular processes occur because of enzymes.

And in fact, if it weren't for enzymes, then the vast majority of cellular processes simply wouldn't happen and therefore we wouldn't be able to exist.

So enzymes, because they are speeding up the rate of reactions, are absolutely critical to us being healthy.

Now, enzymes take a substrate into their active site, process it to break or make bonds, and then release the products.

And all of this function happens within the active site.

Now, enzymes work fastest in their optimum conditions.

So that's at an optimum temperature and also at an optimum pH.

And if we move away from those optimum conditions, the rate of reaction will slow down and may well come to a halt, either because at lower temperatures, enzymes and substrates will collide less frequently and therefore the rate of reaction will be slower, or because at higher temperatures or in different pHs, the active site changes shape, so the enzyme isn't able to catalyse those reactions as effectively as it would be able to do at the optimum condition.

So, maintaining optimum conditions is essential for enzyme rate of reaction and therefore for cell function and our ability to be healthy and survive.

Now, we can see the effect of that if our internal body temperature changes.

So if you recall a time when you have been ill and you have run a fever, you will have known how rotten it feels if your internal body temperature increases above the 37 degrees optimum temperature where it normally sits.

And if you are running a fever, it's an indication that you have an infection and your body is responding to that.

Now, that's a very useful response to have, but if that temperature increases above 40 degrees and is then sustained above that temperature for a long time, then what that will do is cause the enzymes to denature, and that can become very critical quite quickly.

However, increasing our body temperature above 37 degrees doesn't just happen by accident.

It is an important response against pathogenic attack.

So if a pathogen is infecting us, by increasing our body temperature, we may well disrupt some of the activity of some of our body enzymes, which in part makes us feel ill, but we also denature the enzymes of the pathogen as well.

And what that does is reduce the pathogen's ability to cause us harm by reducing its ability to reproduce.

And if it is inhibited to reproduce, if it can't reproduce, then there are fewer pathogens there to cause us harm, and therefore it is easier to deal with the infection.

So raising our body temperature is a really important response to pathogenic attack.

And if you're ill again and have a fever, then I hope you feel grateful for the fact that your body temperature has increased because it is helping you and your body respond to that pathogenic attack, even if it does leave you feeling rather poorly.

So let's just check our understanding.

Which of the following statements explain why enzymes stop working at extremely high body temperatures? Is it A, the rate would decrease because the enzyme's active site has changed shape? Is it B, the rate would decrease because there will be a better fit between enzyme and substrate? Or is it C, the rate will decrease because there are more successful collisions? So which statements explain why? And can you correct the mistakes in the other statements? I'll give you five seconds to think about it.

So did you decide that statement A is correct? What about statement B? Well, this is incorrect because there will be a worse fit.

And what about statement C? Well, that is incorrect as well because there will be fewer successful collisions.

Did you get all of those correct and work out the mistakes? Well done if you did.

So we've seen how a significant increase in body temperature is problematic.

And if a significant increase in body temperature is sustained, it can lead to a condition called hyperthermia.

Hyper means over, and thermia means heat.

So this is where our body temperature is over its ideal temperature.

Now, people who are exposed to sustained high temperatures and without sufficient water risk developing hyperthermia because the body struggles then to lose enough heat to maintain its optimal internal temperature.

And the problem with this is that if it's left untreated, it can lead to death.

Conversely, if our body temperature is reduced and that is sustained, it can lead to a condition called hypothermia, where hypo means under and thermia means heat.

So hypothermia is sustained reduction in body temperature.

And people who have become trapped on mountains or stranded in cold water really do risk developing hypothermia because the body struggles to maintain its optimum temperature because of the cold external surroundings.

And, as with hyperthermia, if hypothermia is sustained and not treated, that too can lead to death.

So you can see how sustaining temperatures outside of the optimum internal body temperature can be very risky indeed.

So let's quickly check that.

Maintaining an optimum internal temperature is important in keeping us alive and healthy.

Is that true or false? So you should have said that that is true, but why? Can you explain that? So you should have explained that maintaining an optimum internal temperature is important because temperatures below the optimum can slow enzyme activity down, and temperatures above the optimum can change the shape of an enzyme's active site.

Did you get the right explanation? Well done if you did.

Maintaining a constant internal optimum environment is essential for us to maintain our health.

And maintaining that constant internal environment, despite the changes that are going on around inside and outside of our body, is called homeostasis.

So homeostasis is this process of maintaining a constant internal environment.

And this is essential for maintaining our health and keeping us alive because we've already seen how moving temperatures away from the optimum can be really very risky indeed.

So let's quickly check that.

Can you complete the gaps in the sentences below? Something is important for maintaining a constant something environment.

Being exposed to very cold temperatures for a long period of time can lead to something and ultimately cause something if left untreated.

I'll give you five seconds to think about the words to go in those gaps.

Okay, so what did you put in those gaps? So homeostasis is important for maintaining a constant internal environment.

Being exposed to very cold temperatures for a long period of time can lead to hypothermia and ultimately cause death if left untreated.

Did you get all four words right? Well done if you did.

So what I'd like you to do now is just to consolidate our understanding by firstly defining the term homeostasis and then explaining why extreme changes away from the optimum body temperature may be so dangerous to our health.

So pause the video, and come back to me when you're ready.

So firstly, I asked you to define the term homeostasis.

So you should have written that homeostasis is the regulation of the internal conditions to maintain optimum conditions for enzyme action and all cell functions.

Now, you may have phrased that differently, but it's about maintaining a constant internal environment.

Then I asked you to explain why extreme changes away from the optimum temperature may be so dangerous to our health.

And you might have written that enzymes are essential for catalysing most cellular reactions and that enzymes work fastest in optimum conditions such as 37 degrees centigrade, which is our internal body temperature.

At temperatures below this, enzyme rate decreases because fewer successful collisions occur between enzymes and substrates, whereas at temperatures above this, the enzyme rate may decrease because the enzyme changes shape.

Now, hyperthermia and hypothermia are caused by exposure to sustained high or low temperatures and can, if left untreated, lead to death.

So just review your work, make sure you've got all of those salient points, and well done indeed.

Okay, let's have a look at the effects of changing internal water content.

So water is fundamental for cell function, and the cytoplasm of cells is mainly made up of water.

And many vital chemical reactions take place within the cytoplasm, so water is essential for cellular processes.

If we have too much water or too little water, this can affect the cell's ability to function.

So maintaining a constant water content within the body is critical for health.

Now, water balance is the term used to describe the concentration of water and mineral ions within the blood.

And the brain monitors water balance and can adjust the amount of water and ions we retain or lose depending on how the blood compares to the cellular levels.

So if the blood has more water than cells do, then we can lose water.

If it has less water than the cells, then we need to gain water and retain it.

Now, water moves between cells and blood plasma by the process of osmosis.

Remembering that osmosis is the net movement of water molecules through a selectively permeable membrane from high to low concentration of water molecules.

And you can see that in the diagram where there is a high concentration of water on the left side of the semipermeable membrane and a lower concentration of water molecules on the right side of the semipermeable membrane.

So the water will move from high to low concentration through the semi-permeable membrane.

Now, if there is a lower concentration of water molecules in the blood plasma, more water will move by osmosis from the cells into the blood plasma.

In other words, water will leave the cells.

Now, this is a problem particularly for animal cells because animal cells are not surrounded by a cell wall.

Now, the cell wall in plant cells offers the cell some structural support, but animal cells do not have that cell wall and so lack that structural support.

Now, if significant quantities of water leave the cell, then the cell will shrink and shrivel.

And by doing so, this may well impair the ability of that cell to carry out its functions.

Not only because there is now less water within the cytoplasm, but also because its shape is distorted.

Conversely, if there is a higher concentration of water molecules in the blood plasma, then water will move by osmosis from the plasma into the cells.

So in other words, more water will enter the body cells.

So what will this mean? Now, if significant quantities of water enter the cell, because the cells of animals do not have a cell wall, there is nothing to stop it from swelling and swelling until it bursts.

So if too much water enters a cell, the cell will swell up and burst, a bit like a balloon.

Now obviously, this has a critical impact on the cell's ability to function because it is now burst and broken.

So too much water can be very damaging to animal cells as well.

So let's quickly check our understanding.

Which diagrams show the effects of a cell when the concentration of water molecules in the blood plasma increases? I'll give you five seconds to think about it.

So if there is more water in the blood plasma than inside the cells, then water will enter the cell and the cell may burst.

That means that images B and D are correct.

Did you spot those correctly? Well done if you did.

Now, water can be lost in a number of ways from the body.

The main way of losing water is through urination.

But water can also be lost from the skin by sweating, and we also exhale water from our lungs when we breathe out.

Now, the brain can control the amount of water that we lose through sweating and urination, but it cannot control the amount of water that we lose from our lungs through exhalation because that is an accident, really.

We don't want to lose water when we breathe out, but because our lungs are moist, that is what is happening.

So our brain can't control that water loss, but it can control the water loss from urination and from sweating.

Now, if we lose more water than we take in, it can lead to a condition called dehydration where we have less water within our body than we ought to have.

Now, less water in our body means that there will be insufficient water within our cells for chemical reactions to take place sufficiently.

And we've already seen how this can affect cell structure.

Now, mild dehydration is easy enough to treat because mild dehydration makes us feel a bit thirsty and so we can have a drink.

But if we lose 15% or more of our body water, then this, if untreated, can lead to death.

So you can see how maintaining water content balance is really critical for cell function and for our health.

So, let's quickly check our understanding.

The brain does not control the amount of water lost from the body through, A, exhaling, B, urination, or C, sweating? I'll give you five seconds to decide.

Okay, so you should have said that the brain does not control the amount of water lost from the body through exhaling.

Well done if you got that right.

So what I'd like you to do now is to firstly define the term osmosis.

Then I'd like you to describe the role of water in cells and the effect of too little or too much water on cells.

And then I'd like you to consider this, that people over the age of 50 may have a decreasing sense of thirst.

So can you use this to explain why intense heat in summer may be particularly dangerous for those over the age of 50? So pause the video, and come back to me when you're ready.

Okay, let's see how you got on.

So firstly, I asked you to define the term osmosis.

So you should have said that osmosis is the net movement of water molecules through a selectively permeable membrane from high to low concentration of water molecules.

Then I asked you to describe the role of water in cells and the effect of too little and too much water on cells.

So you should have said that cytoplasm is mainly made of water, and many chemical reactions take place in the cytoplasm.

So that's the role of water in cells.

Now, water moves by osmosis from areas of higher to lower concentration of water molecules.

And if there is less water in the blood plasma, more water will leave cells by osmosis, and this will cause cells to shrivel.

Whereas if there is more water in the blood plasma, then more water will enter cells, and they will swell up and may burst.

Now, both of these processes may prevent the cell from carrying out its functions effectively.

So just review your answers and make sure you've got all of those salient points, and well done indeed.

Then I asked you to consider this, that people over the age of 50 may have a decreasing sense of thirst.

So can you use this to explain why intense heat in summer may be particularly dangerous for those over the age of 50? So you may have written that intense heat makes it difficult for the body to cool down effectively, and therefore sweating increases, so more water is lost from the body than normal.

Now, elderly people who have a reduced sense of thirst may not drink enough water to keep themselves hydrated.

And in intense heat, this can lead to significant dehydration, which can, if untreated, lead to death.

And this is why intense heat in summer may be particularly dangerous for those over the age of 50.

Did you get all of those ideas written down? Pop anything down that you missed out, and well done indeed for considering that situation.

So let's move on to the last section of our lesson today then, which is about how the body maintains internal constant conditions.

So the maintenance of constant internal condition, called homeostasis, is controlled through nervous and endocrine, that's hormonal, responses.

And the brain oversees the coordination of these responses.

Now, control systems always include three significant elements.

Receptors, which detect changes in the environment, a coordination centre, such as the brain or the spinal cord or the pancreas, that receives that information from the receptors and processes it, and then effectors, which are muscles or glands that bring about the response to restore optimum conditions.

So let's quickly check our understanding of this.

What I'd like you to do is match the name of the part of the control system with the example.

I'll give you five seconds to think about it.

So you should have matched the receptor to the temperature sensor, the coordination centre to the brain, and the effector to the sweat gland.

Well done if you got all of those right.

Now homeostasis, the maintenance of constant internal conditions, requires processes that can work against each other in order to bring optimum conditions back.

Now homeostasis, the process of maintaining constant internal conditions, requires processes which can work against each other in order to return back to optimum conditions.

So, if we are too hot, we need a process that is going to cool us down, and if we are too cold, we need a process that is going to warm us back up again.

And processes that are working against each other are called antagonistic.

So these effectors are antagonistic, they are working against each other.

So let's consider a situation where you have become too hot.

How did your body cool you down? And what about when you became too cold? How did your body warm you up? Just think about that for a moment, and can you identify the antagonistic effectors and their effects? So you might have remembered that when you got too hot, you sweated.

So your sweat glands, the effectors, produced an effect of cooling us down by producing sweat.

And that process of evaporation of sweat from our skin helped cool us down, giving us the effect of cooling.

Whereas when we got too cold, you may well have remembered that you shivered.

And so shivering is the effector, and this generated heat because our muscles were contracting and relaxing quickly, and that helped to warm us up, having the effect of warming us up.

So we can conclude, therefore, that sweating and shivering are antagonistic effects caused by antagonistic effectors, the sweat glands and the muscles.

Now we can model how these antagonistic effects work by trying to maintain a beaker of water at a constant temperature of, say, 40 degrees.

So if our temperature moved away from the optimum, let's say it cooled down, how would we heat the water back up? Or if it got too hot, how would we cool it back down again? So have a think about that.

How would we respond to those conditions in the lab? So you might have thought that if it cooled down, then we would heat the water back up again using a Bunsen burner.

But if the water got too hot, then perhaps we could add ice cubes to it in order to cool it back down again, therefore maintaining the constant condition of 40 degrees centigrade.

So in this model, we can see how antagonistic effects are enabling us to maintain a constant condition.

So, which of these examples is an example of a pair of antagonistic effects? Is it A, insulin, which decreases blood sugar, and glucagon, which increases blood sugar? Is it B, factor VIII, which clots blood, and fibrinogen, which seals cuts to stop bleeding? Or is it C, sweating to cool the body down, and shivering to warm the body up? I'll give you five seconds to think about it.

Okay, so you should have said that A is an example of a pair of antagonistic effects, where insulin decreases blood sugar and glucagon increases blood sugar, so they are working against each other, and sweating and shivering are also antagonistic effects, cooling the body down or warming the body up.

Well done if you spotted both of those.

Okay, what I'd like you to do now is to define this term antagonistic with examples of effectors and effects.

Then I would like you to explain, with an example, how antagonistic effectors maintain homeostasis.

So you may wish to use the control of body temperature, but you could choose an alternative example if you prefer.

So pause the video, and come back to me when you're ready.

Okay, let's see how you got on then.

So firstly, I asked you to define the term antagonistic with examples.

So you should have said that antagonistic effectors and effects work against each other and that effectors include sweat glands and muscles, and examples of effects, including sweating and shivering to control body temperature.

Now, you may have included other examples, that's absolutely fine, but as long as they are examples where they are working against each other.

Then I asked you to explain, with an example, how antagonistic effectors maintain homeostasis.

So you might have included that homeostasis is about maintaining a constant internal environment and that antagonistic effectors work against each other in order to do this.

Now, when our body temperature increases, sweat glands produce sweat, and evaporating sweat reduces our body temperature back to normal.

Whereas when our body temperature decreases, our muscles shiver, and when we shiver, our muscles contract and relax really quickly, which generates heat, and this increases our body temperature back to normal.

So well done if you've managed to include all those points.

Include anything else that you might have missed.

So, we've come to the end of our lesson.

And in our lesson today, we've seen that our body is maintained at a constant, optimum internal state, and this maintenance is called homeostasis.

And changes away from this state are quickly adjusted using antagonistic effectors and their effects.

And this is important because it preserves optimum conditions for enzyme activity, including internal body temperature.

It also manages water balance.

So cells neither swell to bursting or shrink due to the effects of osmosis, which would ultimately prevent cellular processes from working effectively.

So we've seen how changes away from optimum conditions, if they are sustained, can cause conditions such as hyperthermia, where we're too hot, hypothermia, where we're too cold, and dehydration, where there's too little water.

And, if left untreated, these can lead to death.

So I hope you've enjoyed our lesson today.

Thank you very much for joining me, and I hope to see you again soon, bye!.