Lesson video

Hi, I'm Mrs. Hudson, and today I'm going to be teaching you a lesson called "Adrenaline, Thyroxine, and Negative Feedback." This is a biology lesson and it comes under the unit titled "Coordination and Control, Hormones, and the Human Endocrine System." The outcome of today's lesson is: I can describe the roles of the hormones, adrenaline, and thyroxin in the human body, and explain what is meant by negative feedback.

There will be some key words that will be used frequently during today's lesson and they are adrenaline, thyroxin, negative feedback, and gland.

Let's have a look at what those words mean.

Adrenaline is a hormone secreted by the adrenal glands in times of fear or stress.

Thyroxin is a hormone secreted by the thyroid gland that stimulates the basal metabolic rate.

Negative feedback is a mechanism where changes to conditions cause an action to reverse the change keeping conditions stable.

And a gland is an organ or tissues that produces and secretes substances such as hormones.

Today's lesson is going to be split up into three parts.

In the first part of the lesson, we're going to be looking at adrenaline and its effects on the body.

Then, we're going to move on to look at negative feedback.

And then finally we're going to look at thyroxine and TSH.

Let's get going with the first part of the lesson though, adrenaline and its effect on the body.

So you can see a picture here of the endocrine system in a female.

Can you remember the name of the circled glands? Those are the adrenal glands.

And the adrenal glands are located at the top of both kidneys.

The adrenal glands secrete the hormone adrenaline that is carried rapidly around the body in the blood plasma.

So the adrenal glands secrete the hormone adrenaline.

You might have heard of the word adrenaline before.

Can you remember in what situations adrenaline might be secreted? If you are stressed, excited, angry or frightened, your adrenal glands secrete the hormone adrenaline.

Adrenaline is secreted to prepare the body for rapid action, sometimes known as fight or flight.

So in these situations, your body might release adrenaline if you are stressed, if you are very excited, if you are angry or if you are fearful.

And we can see in that picture there that the younger girl at the front looks very scared, but the lady behind her looks like she's really enjoying it, so she could be excited and also releasing adrenaline.

Also wanted to point out in this slide that animals, not just humans, do release adrenaline as well.

Once secreted, adrenaline acts quickly causing the heart rate and breathing rate to increase, which supplies muscles with more glucose and oxygen for respiration.

Glycogen in the liver and muscle cells is converted into glucose for respiration.

And also you have a mental awareness to make decisions very quickly.

Blood will also be diverted away from your digestive system and moved to big muscles in the limbs.

And also the pupils, which is the black circle in your eyes, the pupils of your eyes will dilate, which means to increase in size to let in more light.

This allows the retina to send more information to the brain about your surroundings.

And you can see in that image there that the pupils' size is much larger.

Let's check out understandings so far.

Which glands secrete adrenaline? A, kidneys, B, adrenal, or C, liver and muscle cells.

This is B, the adrenal glands.

Next question is a true or false question.

Adrenaline causes breathing and heart rate to increase, true or false? And then say why.

This is true.

Adrenaline does cause breathing and heart rate to increase, and the reason why this happens is because the heart rate and breathing rates increase which supplies muscles with more glucose and oxygen for respiration.

Fantastic job if you manage to get those rights.

Well done.

We're ready now to move on to the first task of the lesson, task A.

In the first part, you need to name the glands that are circled and state the hormone that they release.

And then number two, describe some emotions that might lead to adrenaline being released.

And then number three, complete the table to show the effects adrenaline has on the body.

You've got the parts of the body affected and a description of the response it causes.

So the part of the body affected is the breathing and the heart rate.

Then you've got the pupils, the liver and muscle cells, and the digestive system and muscles.

So have a go at those now.

Give as much detail as possible and then press Play when you are Ready for me to go through the answers.

Let's see how we did.

So for part one, the glands that are circled are the adrenal glands and they sit above the kidneys and secrete the hormone adrenaline.

Adrenaline quickly prepares the body for response in stressful situations.

And you might have written there as well that it prepares you for fight or flight mode.

For question two, some emotions that might lead to adrenaline being secreted.

So adrenaline is most likely to be released when a person is scared, stressed, excited, or angry.

Fantastic job if you've got those right.

Moving on to part three.

So breathing and heart rate a description of what adrenaline causes, breathing and heart rate increases which supplies muscles with more oxygen and glucose for respiration.

Pupils, the pupils of your eyes dilate, which means that they get bigger in size to let in more light, allowing you to process the surroundings in more detail.

Liver and muscle cells.

So glycogen in liver and muscle cells is converted into glucose.

Glucose is used in respiration to provide energy to muscles.

And then finally, digestive system and muscles, blood can be diverted away from your digestive system and move to big muscles providing reactants for respiration.

Really great job if you manage to get those right.

If you need to pause the video to add in any detail into your answers, then please do, but we're going to move on now to the second part of our lesson.

Really great job so far.

Well done.

So we know about adrenaline and its effect on the body.

Let's have a look now at negative feedback.

Homeostasis involves keeping certain conditions in the body within an ideal range.

Negative feedback is a mechanism where changes to conditions cause an action to reverse the change keeping conditions stable.

So what this means is your body is working to keep certain conditions in your body relatively constant and close to that ideal range.

Sometimes those conditions will change, so they could increase or decrease.

And negative feedback is a mechanism where the body reverses that change to bring levels back to normal.

So here, if this was the ideal level of a condition in a body, you can see that it varies away from the ideal.

So there's an increase.

So negative feedback means the change is reversed and the body responds by decreasing the levels back to normal.

And also it's not just an increase and lowering levels back to normal, but if the ideal level decreases, then the changes reversed and the body responds by increasing the levels back to normal.

Negative feedback is all about the body responding to changes and bringing about an effect that reverses the change, bringing conditions in the body back to normal.

So this is a little flow chart that will help you to understand the process and mechanism of negative feedback.

So if you have the ideal level in the body, then there could be an increase in that level.

So the level increases.

The receptors will detect that change, so they detect the increase, and then the body responds to decrease levels and they will go back to the ideal range.

So your body has detected the change and then brought about a change to reverse it and bring levels back to normal.

Sometimes as well the levels will decrease in the body.

Receptors detect that change, and then there's a response to increased levels, so that they get back to the ideal again.

Glucose regulation is controlled by a negative feedback loop.

Changes are detected and reversed to keep levels within the ideal range.

If this was the ideal level here, if glucose increases, the pancreas detects the change and then insulin is secreted, which decreases levels back to normal.

And also sometimes glucose will decrease.

The pancreas detects that change.

Glucagon is secreted, which increases blood glucose levels and they go back to normal.

So glucose regulation is an example of a negative feedback loop.

Negative feedback loops ensure that there are only small variations away from the ideal range.

So here we've got a graph which is showing you blood glucose concentration over a certain time period, and the dotted line is showing you the ideal level of blood glucose.

But what we can see is that that level changes naturally over time due to eating, fasting, and also exercise.

Now we can see here where there are increases in the blood glucose, insulin is secreted, which causes blood glucose to return back to normal.

So after we've got an increase, insulin is secreted and levels will decrease back to the ideal range.

And in a similar way, when blood glucose is decreasing, glucagon is secreted causing blood glucose levels to return back to normal and they increase back up to that ideal range.

Let's check our understanding of that so far.

What does negative feedback ensure? A, that changes are only decreased back to normal, B, that changes can go beyond the ideal range, or C, that changes Are reversed back to normal.

This is C, that changes are reversed back to normal.

It's not A, because that says that changes are only decreased, whereas changes could be increased back to normal as well.

So it's just that when the body detects a change, if that's an increase or a decrease, the body is reversing that change back to normal.

Great job if you got that right.

We're ready now to move on to task B.

And in the first part, Andeep is describing negative feedback.

What is correct about what Andeep has said and what has he misunderstood? And this is what Andeep has said.

"Negative feedback is only used in the body when certain conditions increase.

The body detects this increase and then decreases levels, reversing the change." And then in the second part of task B, you've got this flow chart shows how negative feedback works and can you fill in those missing labels? I'm sure you're gonna do a really great job of this.

Pause the video, give it your absolute best go and then press Play when you're Ready for me to go through the answers.

Let's see how we did.

So some of what Andeep is correct, but he also has misunderstood something.

So Andeep is correct in saying that negative feedback involves the body detecting changes and then reversing these changes.

However, negative feedback involves detecting increases and decreases in certain levels.

The body then responds to reverse these changes and bring levels back to normal.

What Andeep is saying is that negative feedback is only used in the body when certain conditions increase, but if we're talking about blood sugar levels, it could be that blood sugar levels have decreased and the body has to reverse this change back to normal.

So well done if you recognise that.

And then for part two, filling in these missing labels, if the levels increase, then the receptors detect this change, the responses to decrease levels and then you will get back to the ideal range.

And then in opposite to level increases, you'll have the level decreases, the receptors detect the change and the responses to increased levels.

Fantastic job if you manage to get those right.

Well done.

Really great job so far.

So we know what adrenaline and its effects on the body are.

We've just learned about negative feedback.

And let's look at another example of negative feedback, which involves thyroxin and TSH.

So here again we've got the endocrine glands in a female and then one of those glands is circled.

Can you remember the name of this circled gland? This is the thyroid gland.

Well done if you Remember that.

The thyroid gland controls the metabolic rate of the body and secretes the hormone thyroxin.

Metabolic rate is the rate of all chemical reactions in the body.

So overall on this slide we need to know, the thyroid gland secretes thyroxine and this controls the metabolic rate of the body.

Thyroxine plays an important role in growth and development, but in adults the levels of thyroxine in the blood usually remain stable.

The regulation of thyroxine in adults is controlled by a negative feedback loop and it involves the pituitary gland, which we can see circled there, it's in the brain, and also the thyroid gland, which is located in the neck.

The pituitary gland secretes a hormone called TSH, thyroid stimulating hormone.

You can just remember TSH, but it is useful to know that that stands for thyroid stimulating hormone.

And the thyroid gland, we already know what hormone that secretes.

Can you remember? The thyroid gland secretes thyroxine.

So, well done if you remembered that.

When levels of thyroxine in the blood decrease, sensors in the brain detect this and respond by increasing the secretion of TSH from the pituitary gland.

TSH causes thyroxine to be made in the thyroid gland.

So when levels of thyroxine decrease, our body wants to make more thyroxine.

And TSH causes a thyroid glands to create thyroxin.

So therefore you want to increase the accretion of TSH.

So here, if thyroxin levels decrease, the pituitary gland will secrete TSH, and then that acts on the thyroid glands.

And the thyroid gland increases thine secretion to bring levels back to the ideal range.

Once thyroxine has increased, the pituitary gland will stop secreting TSH, and this is negative feedback.

So this image here is showing you the same sequence of events in the previous slide.

If thyroxin levels decrease, the pituitary glands secretes TSH, which then acts on the thyroid gland to increase thyroxin production.

And once thyroxin production has increased so much, thyroxin levels will return to normal.

And then this will stop the pituitary gland from secreting any more TSH.

And so that's the change being reversed and that is negative feedback.

When thyroxine levels in the blood increase, sensors in the brain detect this and respond by inhibiting the amount of TSH secreted from the pituitary gland.

And then this decreases the amount of thyroxine that is made in the thyroid gland.

So when the thyroxine levels in the blood are too high, our body wants to respond by reducing the amount of thyroxine.

And then this is done by inhibiting the amount of TSH to stop the thyroid gland releasing thyroxine.

So here, if thyroxine levels increase, the pituitary gland will inhibit the production of TSH, and then this will mean that the thyroid gland is not stimulated to make thyroxine and levels of thyroxine will decrease back to the ideal range.

This flow chart shows the negative feedback loop for thyroxine.

So we're starting here with the ideal level of thyroxine.

And if thyroxine levels increase, the pituitary gland will inhibit TSH and then the thyroxine level will decrease, because the thyroid gland will not be stimulated to produce thyroxin.

And that will bring thyroxine levels back towards the ideal range.

And in opposition to this, if thyroxine levels decrease, the pituitary gland will secrete TSH and that TSH will stimulate the thyroid gland to increase the production of thyroxine and thyroxine levels will increase and we'll get back to that ideal range again.

Negative feedback keeps the level of thyroxine in the blood stable.

So here we've got a graph showing thyroxine concentration in the blood over a period of time.

And we can see here that that there's an increase and then a decrease, and then it goes down and back up again.

And this dotted line here is showing you roughly the normal concentration of thyroxine that your body would want to have.

So a point one in this graph here, the thyroxine level is increasing.

And so what will happen is the body will inhibit TSH.

And what this does is it doesn't stimulate the thyroid gland to produce thyroxine at point three in the graph, thyroxine levels will decrease.

And then at point four thyroxine level is decreasing.

It's gone below normal concentration.

And so the body responds by secreting TSH, and remember that will stimulate the thyroid gland to produce thyroxine, and so at point six, the thyroxine levels will start to increase back towards that normal concentration.

And this is showing you the negative feedback loop controlling thyroxine levels in the body.

Let's check our understanding of that.

So which gland in the brain secretes TSH? A, the thyroid, B, the adrenal, or C, the pituitary.

This is C, the pituitary gland.

That's the only gland here that's located in the brain.

That adrenal glands sit on top of the kidneys and the thyroid glands secretes thyroxine and is in the neck region.

So well done if you got that right.

True or false, when thyroxine levels are too low, TSH is secreted from the pituitary gland? Is that true or false? And then say why.

This is true.

So when thyroxin levels are low, TSH is secreted from the pituitary gland, and this is because TSH stimulates the thyroid gland to secrete thyroxine to increase levels back to normal.

Fantastic job if you remembered that and got that right.

We've ready now to move on to the final task of our lesson, task C.

And in part one, you need to say which statements about the control of thyroxine are correct.

A, regulation of thyroxine is not an example of negative feedback.

B, the pituitary gland secretes TSH.

And C, TSH is inhibited when thyroxine levels are too low.

Then in part two you need to correct the incorrect statements from task C part one and explain why the statements are incorrect.

And then part three, what is the role of the thyroid gland? And then finally in part four, you need to use the diagram to explain how the body responds to increases and decreases in the level of thyroxine.

And you've got a flow chart here, which is showing you the pituitary gland to the thyroid gland, to thyroxine, and then changing thyroxine level back up to the pituitary gland.

So you need to give us much detail as possible here to explain how the body responds to increases and decreases in the level of thyroxine.

I'm sure you're gonna do a fabulous job.

Pause the video and then press Play when you are ready for me to go through the answers.

Let's see how we did.

So in A, regulation of thyroxine is not an example of negative feedback.

This is incorrect.

For B, the pituitary gland secretes TSH, this is correct.

And for C, TSH is inhibited when thyroxine levels are too low, this is incorrect.

So moving on to part two where we had to correct those incorrect statements.

So first of all, the pituitary gland is an example of negative feedback, because when levels change, the body either secretes or inhibits TSH to bring thyroxin levels back to normal.

And then second incorrect statement, when thyroxine levels are too low, TSH will be secreted, as this stimulates the thyroid gland to secrete thyroxine increasing levels back to normal.

And then part three, what is the role of the thyroid gland? The thyroid gland controls the metabolic rate of the body and secretes the hormone thyroxin.

Metabolic rate is the rate of all the chemical reactions in the body.

Fantastic job if you manage to get those right.

And then moving on to part four, so explain how the body responds to increases and decreases in the level of thyroxin.

Regulation of thyroxine is controlled by negative feedback.

When thyroxine levels increase, the pituitary gland inhibits the production of TSH, it stops the thyroid gland from secreting thyroxine and levels decrease back to normal.

When levels of thyroxine are back to normal, the pituitary gland will stop inhibiting TSH.

This is negative feedback.

And then looking now at when thyroxine levels decrease, the pituitary gland secretes TSH, which stimulates the thyroid gland to produce thyroxine increasing levels back to normal.

Once thyroxine levels are back to normal, the pituitary gland will stop secreting TSH, and this is negative feedback.

There's a lot of information in the final task, so if you want to pause the video to check for your answers and add in any extra detail, then please do.

But on the next slide, we're going to summarise everything that we've learned so far in today's lesson.

So today's lesson is all about adrenaline, thyroxine, and negative feedback.

And at the beginning of the lesson we spoke about adrenaline and we said adrenaline as a hormone that is secreted by the adrenal glands during times of stress, fear, excitement, and anger.

Adrenaline brings about a number of responses in the body, such as increased breathing rate and heart rate, glycogen converting into glucose, blood diverting to large muscles, and pupils dilating.

Negative feedback is a mechanism where the body responds to change and brings about an effect to reverse the change bringing levels back to normal.

The regulation of thyroxine is controlled by negative feedback.

When thyroxine is low, the pituitary gland secretes TSH, that stimulates the thyroid to produce thyroxin.

And when thyroxine is too high, the pituitary gland inhibits TSH, which stops the thyroid gland secreting thyroxine.

And then, will bring those levels back to normal again.

I've really enjoyed today's lesson.

I hope you have to, and I look forward to seeing you next time.