Lesson video

This lesson is called, The roles of the nervous and endocrine systems in controlling water balance, and is from the unit, Coordination and control, maintaining a constant internal environment.

Hi there, my name's Mrs. McCreedy, 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 describe the roles of the nervous and endocrine systems in controlling water balance in the human body.

We're gonna come across a good number of key words in today's lesson, 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 roles of the hypothalamus, the pituitary gland, and ADH, before we consider the effect of alcohol on water balance.

So, are you ready to go? Let's get started.

Now, when our body conditions change, it is important that our body responds accordingly, so changes in the external and internal environment that may impact our health and the ability for our body to function need to be responded to.

Now, the responses to these changes, both internal and external, are coordinated by the nervous and the endocrine systems, and these two systems work together to help regulate body conditions.

Now, when we're talking about maintaining water balance, we're talking about the function of the kidneys.

Now, blood is filtered by the kidneys, and water, ions and nutrients are selectively reabsorbed.

Waste products are removed and these are sent for storage down to the bladder as urine before we excrete them.

Now through this process, the kidneys are able to adjust the water balance within the blood plasma and ensure that our water balance is maintained at a constant level.

But how is it that the kidneys detect changes in the water balance? Well, the answer is they don't.

The brain is involved in doing that instead.

So the nervous system has the function of detecting the change and the kidney has the role of affecting any instructions in order to maintain the balance.

Now, let's quickly check our understanding.

To which organ system do the kidneys belong? Is it A, the endocrine system, B, the excretory system, or C, the nervous system? I'll give you five seconds to decide.

Okay, so you should have decided that the kidneys belong to the excretory system.

Well done.

Now, in all systems that control an environment, there must be three significant features to them, and this is true of functional systems like computers and body systems as well.

So there must be a receptor that can detect changes in the environment.

There must be a coordination centre that directs the response on receipt of those detected changes, and there must be an effector that delivers the change required.

Now, all of these parts must be present within an effective system, and there must also be a way of moving the messages from the receptor to the coordination centre and then from the coordination centre to the effector effectively.

So the way that these messages can be moved may be via neuron or via the bloodstream through the endocrine pathway.

Doesn't matter which, and it can be a mix of both within one system, provided that the messages can be moved from one place to the next effectively.

So, let's have a look at how that functions for maintaining water balance.

So, let's start with a receptor.

So, it's the receptor that detects changes in the water balance, and we're specifically at this point looking at changes in water balance within the blood plasma.

Now these changes are detected by receptors located within the hypothalamus.

The hypothalamus is a part of the brain.

So, the receptors detect changes in water balance in the blood plasma as the blood is circulating the body.

Now, when there is less water in the blood, the hypothalamus detects that reduction in concentration of water molecules or increase in solute concentration, and sends a message to the coordination centre.

Now, the coordination centre is another section of the brain called the pituitary gland.

And the pituitary gland isn't very far away from the hypothalamus, but it is a different section.

Now, the pituitary gland is the coordination centre and that is part of the endocrine system.

Although it sits within the brain, it's actually responsible for managing hormone levels rather than sending out nervous signals.

And it's the pituitary gland that coordinates the response to changes in water balance.

So, on a change in water balance, as identified by the receptor within the hypothalamus, the pituitary gland is informed about this via the nervous system, and then coordinates the response via the endocrine system.

So, when the pituitary gland is nervously stimulated, it's secretes a hormone called ADH, anti-diuretic hormone.

Now, ADH is a messenger, and it, because it's a hormone, travels via the blood to the kidneys, which are the effector in this system.

So the effector, the kidneys, respond to changes in ADH levels within the blood.

So, if there is more ADH in the bloodstream, then the kidneys will detect that and that will cause an increase in the permeability of the kidney tubules.

What this means is that more water will be reabsorbed into the blood plasma, and that means that less water is excreted and therefore the urine becomes more concentrated.

So, the effect of ADH on the kidneys is to cause more water to be reabsorbed into the blood plasma and therefore urine to become more concentrated.

So, when there is less water in the blood, let's just summarise that, the hypothalamus in the brain detects this reduction in water concentration and it stimulates the pituitary gland via a nerve signal, and the pituitary gland releases, secretes, the hormone ADH.

ADH travels via the bloodstream to the kidneys and increases the permeability of the kidney tubules.

So, this means that more water is reabsorbed, less water is excreted, blood plasma concentrations return to normal and urine becomes more concentrated.

So, let's quickly check our understanding.

Which part of the body secretes ADH? Is it A, the blood plasma, B, the hypothalamus, C, the kidney, or D, the pituitary gland? I'll give you five seconds to think about it.

Okay, so which part of the body secretes ADH? You should have said the pituitary gland.

Well done if you got that correct.

And now, I'd like you to start with the hypothalamus and put these stages in order to describe how the kidney is made to reabsorb more water.

So, part A is the pituitary gland is stimulated to secrete ADH.

B is more water is reabsorbed.

C is the hypothalamus detects an increase in solute concentration in the blood plasma, and D is ADH increases the permeability of the kidney tubules.

But which order do they go in? I'll give you five seconds to think about it.

So, let's put these in order then.

So we're starting off with C, the hypothalamus, then we're going to A the pituitary gland.

Then we're going to D, ADH, increasing permeability.

And finishing off with B, more water being reabsorbed.

Did you get them in the right order? Well done if you did.

Now, we've seen what happens when there is less water in the blood, what about when there is more water in the blood? So if there is more water in the blood, if water concentration has increased, then this change is also detected by the receptors within the hypothalamus, but this time it reduces the frequency of the signals sent to the pituitary gland via the nervous system.

This means that the pituitary gland secretes less ADH, and this makes the kidney tubules less permeable, which means less water is reabsorbed, more water is excreted and the urine becomes more dilute.

So, when there is more water in the blood, we can afford to get rid of it via our urine, and so less ADH is secreted, that means that the kidneys reabsorb less and so more water can be excreted.

So, let's quickly check our understanding there.

Anti-diuretic hormone, ADH, decreases the permeability of the kidney tubules, true or false? Okay, so you should have said that that is false, but why? So, you should have thought that ADH increases the permeability of kidney tubules and therefore increases the amount of water reabsorbed, so less water is excreted as urine.

And you might be able to work this out by understanding what this term diuretic means.

So, a diuretic increases the amount of urine produced, and ADH acts in the opposite direction, which is why it's called anti-diuretic.

It is not increasing the amount of urine, it decreases the amount of urine, and it decreases the amount of urine by increasing the permeability of the kidney tubules.

So, what I'd like you to do now is to complete the diagram by adding labels to the hypothalamus and the pituitary gland, and then add arrows showing how these interact between the different parts of the brain and the kidneys, including the use of ADH, and the effect on urine volume.

Then I would like you to add the numbers of the statements into the boxes of the diagram to show how water balance is maintained.

So pause the video and come back to me when you are ready.

Okay, let's see what you've done then.

So firstly, I asked you to complete the diagram adding the hypothalamus and the pituitary gland, and then you should have linked that with an arrow from the hypothalamus to the pituitary gland.

Then the pituitary gland is secreting ADH to the kidneys, so that's another arrow and label, and then the final label and arrow with urine being produced.

Then I asked you to add the numbers to the statements to show how water balance is maintained.

So, for an increase in water concentration, you should have started off with statement four.

The pituitary gland secretes less ADH.

Then move to five, which is, the kidney reabsorbs less water.

Before finishing with number one, a large volume of dilute urine is produced.

Then for the decrease in water concentration, you should have started off with statement two, the pituitary gland secretes more ADH.

Then moving to three, the kidney reabsorbs more water.

Before finishing with statement six, a small volume of concentrated urine is produced.

Now did you get those around the right way? It can be a little bit confusing, but make sure you've understood the role of ADH on permeability of kidney tubules.

And well done.

So let's move on to see the effect of alcohol on water balance.

Now, we've already seen how water balance is crucial to be maintained.

It's maintained by the effect that kidneys have on the amount of water within the blood plasma, and this is coordinated by the detection of the hypothalamus and the coordinated response of the pituitary gland in the brain.

And the effective coordination of all of these parts of the system is really critical to make sure that our water balance in the blood plasma is maintained, and therefore we maintain our health and are able to survive.

Now when alcohol is consumed, it suppresses the production of ADH from the pituitary gland.

So this means that less ADH is produced, the kidney tubule permeability is reduced, therefore less water is reabsorbed into the blood plasma and more water is excreted.

Now, that might sound okay because we are consuming liquid whilst we're consuming alcohol.

But if excessive quantities of alcohol are consumed, then this can become really quite problematic.

Because if excessive quantities of alcohol are consumed, then ADH production is inhibited and the amount of water excreted by the kidneys increases as well and can lead to dehydration.

Now, dehydration if sustained and significant can lead to death, and this is because of the effect that dehydration has on the osmotic balance of the blood plasma and the cells.

So, let's look at this in a little bit more detail.

So, osmosis is the net movement of water from an area of higher concentration to an area of lower concentration through a selectively permeable membrane.

And we can see in the diagram there that it's higher, water is in higher concentration on the left, lower concentration on the right, and so moves from left to right through the selectively permeable membrane in the diagram.

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

So if you can see in the diagram there, there is less water in the blood vessel compared to within the body cell, and therefore water will move from high concentration in the body cell to lower concentration in the blood vessel down the concentration gradient.

Now, reducing the concentration of water inside the cells reduces the cell's ability to perform cellular functions, because water is critical for cellular function, it makes up the majority of cytoplasm, for instance.

So, if this continues to a point where cells can no longer function effectively, it can lead to death, and this is one of the reasons why excessive alcohol consumption is very dangerous.

So, let's quickly check our understanding.

Alcohol stimulates the release of ADH, true or false? So, you should have said that that is false, but why? So, you should have explained that by saying that alcohol suppresses the release of ADH, this leads to less water reabsorption and an increase in water excretion.

So, let's summarise our understanding and consolidate our learning.

Now, Alex's older brother is a university student and he's having a summer party at his flat with friends, they have alcoholic drinks, salty crisps.

It's a hot summer's day, and there's gonna be lots of dancing too.

So using that scenario, I would like you to firstly describe the impact of these factors on the water balance of the people at the party.

Then I would like you to sketch a graph to show how each of these factors will cumulate, add up, to impact blood water balance.

Now by sketching a graph, I mean you don't need to include numbers on the axis, but you do need to label the axis with what you are showing on the X and the Y, and show what's gonna be happening to the concentration of water in the blood plasma as the day goes on.

Then finally, I'd like you to suggest some practical steps that Alex's brother could take to ensure that none of his friends end up dehydrated.

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

Okay, let's see what you've written.

So firstly, I asked you to describe the impact of these factors on the water balance of the people at the party.

So, you should have included that the alcohol will inhibit the release of ADH leading to less reabsorption and more water excretion.

You also should have said that the salt in crisps will increase the solute concentration of the blood, drawing more water out of body cells.

In addition to these factors, hot weather and dancing will increase water loss through sweating.

And cumulatively, all of these factors will reduce the water concentration in the body.

So, just check over your work.

Did you mention all of those factors in your answer? Then I asked you to sketch a graph to show how each of these factors will cumulate, that means add up, to impact blood water balance? So your sketched graph might look a bit like my one with water balance on the Y-axis.

And we're starting off with a normal water balance.

Then as alcohol is drunk, the water balance decreases, it decreases further after eating salty crisps, and further still after sweating due to heat and dancing.

So, there's no numbers on my sketch graph, but there is an idea of what is going to be happening, and I hope your graph shows something similar to that.

Then I asked you to suggest some practical steps that Alex's brother could take.

And you might have suggested that water and ice are provided and people are encouraged to drink a glass of water for every alcoholic drink, for instance.

That may be fruit with high water content such as melon, strawberries, cucumber, are provided for consumption with drinks.

And that the windows are open.

Fans used, shade provided, that sort of thing to keep the area cool.

You might well have added some other suggestions as well, as long as they're sensible and they're going to help Alex's brother keep his friends safe, then that's all fine and I'm sure you've probably been much more creative than I have.

So, well done on all of that.

That was quite a challenging application of understanding.

So we've come to the end of our lesson today, well done for getting through it.

We've seen today that the control of water balance is critical to managing our health, and that receptors in the hypothalamus detect changes in the water balance of the blood plasma so that when there is less water in the blood water concentration decreases and the pituitary gland is stimulated by nerve impulses to secrete a hormone called ADH.

And ADH travels via the blood plasma to the kidney tubules and it increases the permeability of the kidney tubules.

This means that more water is reabsorbed into the blood plasma.

Now, drinking alcohol inhibits the release of ADH, and by doing so, it reduces the amount of water reabsorbed.

This means that urine becomes more dilute, and if excessive quantities of alcohol are consumed, it can lead to dehydration.

So, I hope you've enjoyed our lesson today, and I hope to see you again soon.

Bye.