Lesson video

Hi, I'm Mrs. Hudson, and today I'm going to be teaching you a lesson called "Adrenaline, thyroxine, and negative feedback, including TRH." 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 keywords that are frequently used during today's lesson and they are adrenaline, thyroxin, negative feedback, and gland.

Let's look a little bit closer 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 different parts.

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

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

And then finally we're going to look at thyroxin, TRH and TSH.

But let's get going with the first part of the lesson, "Adrenaline and its effect on the body." So you can see a picture here of the female endocrine glands.

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 pupil size is much larger.

Let's check our understanding 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 managed to get those right, 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 parts 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.

Now have a go at those now, give as much detail as possible, and then press play when you're 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 managed 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 change is 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 flowchart 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 increase 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 flowchart that 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 recognised that.

And then for part two, filling in these missing labels.

If the levels increase, then the receptors detect this change, the response is 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 response is to increase levels.

Fantastic job if you managed to get those right, well done.

Great job so far.

We know about adrenaline and its effects on the body, we've just talked about negative feedback, so let's look now at an example of negative feedback using thyroxine, TRH, and TSH.

So here we've got a diagram of the endocrine glands in a female.

Can you name the circled gland here? This is the thyroid gland.

Well done if you remembered 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 here the thyroid gland secretes the hormone thyroxin and that controls the metabolic rate of the body.

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

The regulation of thyroxine in adults is controlled by a negative feedback loop and it involves the hypothalamus, which is labelled here, and the pituitary gland.

Now both of these are found within the brain.

So the hypothalamus sits above the pituitary gland.

The hypothalamus secretes the hormone called TRH, thyrotropin-releasing hormone.

Now you can just remember the letters TRH, but it is useful to know what they stand for.

So the hypothalamus secretes TRH and the pituitary gland secretes the hormone called TSH, thyroid-stimulating hormone.

So the hypothalamus secretes TRH and the pituitary gland secretes TSH.

And then also another gland that is involved in the negative feedback loop is the thyroid gland located in the neck, and we already know, if you can remember, that the thyroid gland secretes thyroxine.

So those are the three parts of the body and the hormones that they secrete that are involved in the regulation of thyroxine.

When levels of thyroxine decrease, the hypothalamus is stimulated to secrete TRH, which causes the pituitary gland to secrete TSH, and then TSH causes thyroxin to be made in the thyroid gland, which will increase the levels of thyroxin.

So when thyroxin levels decrease, the body wants to respond to increase thyroxine levels, and this is done by the hypothalamus secreting TRH and then the pituitary gland secreting TSH.

If we look at this in a bit more detail, if thyroxin levels decrease, then the hypothalamus will secrete the hormone TRH, and then this stimulates the pituitary gland to secrete the hormone TSH, which acts on the thyroid gland to increase thyroxine production, and then it will bring thyroxine levels back to normal and to that ideal range.

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

So here, if we go through the process again, the thyroxin levels decrease, the hypothalamus will secrete TRH, which causes the pituitary gland to secrete TSH, which acts on the thyroid gland to increase the production of thyroxin.

So overall then what happens is that the thyroxin levels return back to normal and therefore TRH and TSH will stop being produced, so therefore the hypothalamus will not secrete TRH and the pituitary gland will therefore not secrete TSH.

When levels of thyroxin increase, the hypothalamus inhibits the production of TRH and this stops TSH being secreted from the pituitary gland.

So here, if the thyroxin level increases, the hypothalamus will inhibit TRH, which will then inhibit the production of TSH.

And if there's less TSH, that will mean that the thyroid gland is not stimulated to produce thyroxine and therefore it will decrease levels back to the ideal range.

This flowchart shows the negative feedback loop for thyroxine.

So if we start with the ideal level, first of all, there's a change to that level.

In this case, thyroxine levels increase.

This causes the inhibition of TRH and therefore TSH.

The thyroxine levels will decrease and they will return back to that ideal range.

And then, if from the ideal level thyroxine levels decrease, what happens is that the secretion of TRH and TSH is increased, so you get more TRH and TSH being secreted, and this will then increase thyroxine levels because the thyroid gland is stimulated to release thyroxine, and it will increase levels back to that ideal range.

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

So here we have a graph which is showing you thyroxine concentration in the blood against time and over time, and we can see that naturally there are increases and decreases throughout the day of thyroxine.

And this dotted line here is showing you what the normal concentration should be, so your body is always trying to reverse the change back to normal.

So at Point 1 here we can see that the thyroxine level is increasing, and the body's response then is that TRH and TSH are inhibited, which will cause thyroxin levels then to decrease.

And then at Point 4 we can see that the thyroxine level is decreasing and the body's response is to secrete TRH and TSH, which will then increase thyroxine levels back towards that normal concentration.

So our body detects the change and reverses the changes back to normal, and that is negative feedback.

Let's check our understanding of this so far.

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

This is C, the pituitary gland.

The thyroid and the adrenal glands are not located in the brain.

The only other part of the brain we've spoken about is the hypothalamus, but that secretes TRH.

Well done if you got that right.

And then a true or false question.

When thyroxine levels are too low, TRH is secreted from the hypothalamus.

True or false? And then explain why.

This is true.

So TRH is secreted from the hypothalamus when thyroxine levels are too low.

And the reason why, TRH causes the pituitary gland to secrete TSH, which then stimulates the thyroid gland to produce thyroxine to increase levels back to normal.

Really great job if you managed to get that right including the response of why.

We're 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, and these are the statements.

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

B, the pituitary gland secretes TSH.

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

And you've got a flowchart here which is showing you the hypothalamus, pituitary gland, thyroid gland and thyroxine, and then a dotted line going back up to the hypothalamus with change in thyroxine level.

So remember there to talk about increases and decreases in the level of thyroxine.

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

Pause the video and then press play when you're ready for me to go through the answers.

Let's see how we did.

So in part 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, TRH is inhibited when thyroxin levels are too low, this is also incorrect.

So well done if you managed to get those right.

For part two, correcting those incorrect statements.

The pituitary gland is an example of negative feedback because when levels change, the body either secretes or inhibits TRH and TSH to bring thyroxine levels back to normal.

And then the second statement was incorrect.

When thyroxine levels are too low, TRH will be secreted.

It won't be inhibited, it will be secreted.

And this causes the pituitary gland to secrete TSH, which then stimulates the thyroid gland to secrete thyroxine, increasing levels back to normal.

And then for part three, what's the role of the thyroid gland? The thyroid gland controls the metabolic rate of the body and secretes the hormone thyroxine.

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

Fantastic job if you managed to get those right.

Now moving on to part four.

Regulation of thyroxine is controlled by negative feedback.

When thyroxine levels increase, the hypothalamus inhibits the secretion of TRH and this causes the pituitary gland to stop producing TSH.

If there is no TSH, the thyroid gland will not produce thyroxin and levels will decrease back to normal.

Once thyroxin levels are back to normal, the hypothalamus will stop inhibiting TRH.

Well done if you managed to get that right about when thyroxin levels increase, we're going to move now to when thyroxine levels decrease.

When thyroxin levels decrease, the hypothalamus is stimulated to secrete TRH and this causes the pituitary gland to secrete TSH.

TSH causes the thyroid gland to produce thyroxine, increasing levels of thyroxine.

Once thyroxin levels are normal, the hypothalamus stops secreting TRH, and this is negative feedback.

There was an a lot of information in the feedback for this task, so if you need to pause the video and go back to check any of your answers and add in any detail, then please do, then we're gonna summarise what we've learned in the lesson in the next slide.

Great job on today's lesson about adrenaline, thyroxine, and negative feedback.

We started off the lesson by talking about adrenaline and we said that adrenaline is a hormone that is secreted by the adrenal glands during times of stress, fear, excitement, and anger.

Adrenaline causes increased breathing and heart rate, glycogen converted to glucose, and blood diverting to large muscles in the body, and also the pupils dilating, which means getting bigger in size.

We then spoke about negative feedback and we said 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.

And then we spoke specifically about the control of thyroxine being an example of negative feedback, and we said the regulation of thyroxine is controlled by negative feedback.

When thyroxine is low, the hypothalamus secretes TRH, causing the pituitary gland to secrete TSH.

This stimulates the thyroid to produce thyroxine and that will increase thyroxine levels back to normal.

We then said that when thyroxine level is too high, the hypothalamus inhibits TRH, which then inhibits TSH production in the pituitary gland, and this stops the thyroid gland secreting thyroxine and decreases those thyroxine levels back to normal, and an example of negative feedback.

I really enjoyed today's lesson, I hope you have too, and I look forward to seeing you next time.