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Explain Homeostasis

Worksheet Overview

QUESTION 1 of 10

Did you know that even when you’re fast asleep your body is still using energy? 

 

 Image of a boy sleeping

 

 

Even when you're fast asleep, dreaming of not having to wake up early for school, the body still uses so much energy! That's because it has to keep a constant internal environment.

This process of keeping things the same is called homeostasis.  

 

Image of types of homeostasis

 

A series of automatic control systems ensures that the body maintains a constant temperature, steady levels of water and balanced blood sugar levels. It also ensures that levels of particular hormones are kept in check, such as adrenaline and thyroxine.

Homeostasis allows the body’s cells to work at their optimum, meaning that conditions allow them to work at their best. 

The conditions of the environment are always changing. Our body has to respond to these changes, but at the same time ensure that certain internal conditions don't vary too much, otherwise, damage could be caused.

One example is temperature. Environmental temperature is constantly changing - part of a day can be very hot, the next,  very cold. Even slight changes in body temperature can have a major effect on health. If body temperature falls too low, reactions become too slow for cells to survive; too high, and the body’s enzymes are at risk of denaturing. Our organs, such as the heart, liver and kidneys, are maintained at 37°C. This is the core body temperature - our body has to maintain this temperature. This is done by negative feedback

Negative feedback is how the body maintains normal levels. If the level of something rises, control systems will come into place to reduce levels again and if the level of something falls, control systems raise it again.

Negative feedback can be summarised in the flow diagram below:

 

Image of negative feedback loop

 

Adrenaline is a hormone produced by the adrenal glands, located above the kidneys.

Adrenaline triggers the body’s fight-or-flight response. What is the fight or flight response? Let’s find out more below:

In stressful situations, you will find that your heart beats fast and your hands may start to sweat. This is caused by adrenaline. Adrenaline will travel into the blood and act on vital organs such as the heart and brain, and certain muscles. Your heart rate increases and your breathing becomes more rapid, delivering oxygen and glucose at a faster rate for respiration. This gives the body the energy it needs to run away (imagine facing a lion!) or to stand your ground and fight in a stressful and dangerous situation. 

 

Image of fight or flight response

 

 

When adrenaline is released into the bloodstream, it creates many effects:

The pulse rate increases and an increased volume of blood is pumped by the heart. 
There is an increase in the depth of breathing.
Blood vessels supplying the muscles dilate, allowing more blood to pass.

 

These effects allow the body to get ready for a quick response to a situation that could potentially be life-threatening.

In everyday terms, it could be when you have to give a presentation to your class. You might start to feel nervous and your heart could begin to race. Your body will react by delivering more glucose to your cells for respiration, and this will give you the energy you need to present to the class (fight), or you might leave the class deciding not to present (flight). Not exactly life-threatening but still important!

 

Adrenaline is an example of positive feedback. Positive feedback amplifies a change rather than returning it to normal conditions, as in negative feedback.

 

Image of adrenaline positive feedback loop

 

 

Thyroxine is the name of another hormone. It is produced by the thyroid gland. It controls the rate of reactions that occur in your body. It controls the speed at which oxygen reacts with glucose to produce energy for the body -  this is called the metabolic rate.

The amount of thyroxine in the blood is controlled by negative feedback.

 

Image of thyroid gland

 

If the levels of thyroxine are low in the blood, the hypothalamus in your brain releases TRH (thyrotropin-releasing hormone). This causes the pituitary gland to release TSH (thyroid-stimulating hormone), which causes the thyroid to release more thyroxine - the levels of thyroxine go back to normal.

 

Image of thyroid, thyroxine and negative feedback cycle

 

In the following activity, you will explain the role that negative feedback plays in homeostasis.

Why is homeostasis important for the human body? 

 

There are two main systems involved in homeostasis.

 

What are the names of these two systems?

Circulatory system

Nervous system

Endocrine system

Immune system

 

The image below shows the negative feedback cycle in homeostasis.

 

What is X?

 

Image of negative feedback fill in

Body doesn't respond to change

Body activates mechanisms to correct change

Body responds to one change at a time

The graph below shows the body regulating its temperature over time.

 

Describe how the graph is showing negative feedback. 

 

Image of graph showing regulation of body temperature

The temperature of the body has to remain below 37°C

The temperature of the body is low at 36.6°C and continues to rise to 37°C

The body tries to maintain a temperature of 37°C which is the body's optimum temperature

The body doesn't need a specific temperature to function

Which gland is responsible for producing adrenaline? 

 

Image of glands in human body

What are some of the effects of adrenaline when released into the blood? 

Increase in muscle size

Increase in heart rate

Increase in the depth of breathing

Decrease in heart rate

What are thyroxine and adrenaline? 

Neurotransmitters

Blood vessels

Hormones

 

Thyroxine plays an important role in controlling our metabolic rate. The levels of thyroxine are maintained using a negative feedback cycle.

 

Fill in X and Y in the negative feedback cycle below.

 

Image of negative feedback cycle of thyroxine

Column A

Column B

X
Thyroid Gland
Y
Pituitary Gland

Adrenaline is released by the adrenal glands.

 

Complete the positive feedback loop by filling in X. 

 

Image of adrenaline feedback loop

Fight or flight response

Reflex response

Hormonal response

 

The correct levels of thyroxine in the blood have to be maintained. This is an example of a negative feedback loop. 

 

Describe what's happening at A and B in the graph below.

 

Image of graph of thyroxine levels

A: Low thyroxine levels, more TRH and TSH released

A: High thyroxine levels, TRH and TSH release inhibited

B: Thyroxine levels return to normal

B: Thyroxine levels remain high

The sentences below describe homeostasis.

 

Place these sentences in order. 

  • Question 1

Why is homeostasis important for the human body? 

CORRECT ANSWER
EDDIE SAYS
Did you get all the blanks filled in correctly? Were you caught out by that important word in the second blank - optimum? The environment is always changing, so our body needs to work hard to keep conditions the same and at their best. When conditions are at their best for a particular cell in the body, it means that they are optimum conditions for that cell or enzyme to be working.
  • Question 2

 

There are two main systems involved in homeostasis.

 

What are the names of these two systems?

CORRECT ANSWER
Nervous system
Endocrine system
EDDIE SAYS
This was a tricky question, so well done if you got this one correct. The nervous system is important for homeostasis - receptors on neurones will pick up stimuli and pass the message to the central nervous system, which will cause effectors to produce a response to return conditions to their optimum state. The endocrine system is also vital - it is the system that controls the different hormones in your body, like insulin or adrenaline, for example.
  • Question 3

 

The image below shows the negative feedback cycle in homeostasis.

 

What is X?

 

Image of negative feedback fill in

CORRECT ANSWER
Body activates mechanisms to correct change
EDDIE SAYS
Negative feedback is used to maintain a constant internal environment. When a change is detected that upsets the body's natural balance, a response is made that activates mechanisms to correct this and restore things to their optimum level.
  • Question 4

The graph below shows the body regulating its temperature over time.

 

Describe how the graph is showing negative feedback. 

 

Image of graph showing regulation of body temperature

CORRECT ANSWER
The temperature of the body is low at 36.6°C and continues to rise to 37°C
The body tries to maintain a temperature of 37°C which is the body's optimum temperature
EDDIE SAYS
37°C is the optimum temperature for the body's processes and reactions - negative feedback ensures this temperature is maintained.
  • Question 5

Which gland is responsible for producing adrenaline? 

 

Image of glands in human body

CORRECT ANSWER
adrenal glands
adrenal
EDDIE SAYS
The image was a useful visual aid here! To help you remember: adrenal glands → adrenaline Both start with the letter 'A' and contain the word adrenal.
  • Question 6

What are some of the effects of adrenaline when released into the blood? 

CORRECT ANSWER
Increase in heart rate
Increase in the depth of breathing
EDDIE SAYS
Adrenaline does affect strength in the short term, but doesn't necessarily make your muscles bigger! It's why you'll often hear in life-saving emergencies, of people doing incredible things like lifting heavy objects. Adrenaline does increase your heart rate and the depth of your breathing to prepare your body for fight or flight.
  • Question 7

What are thyroxine and adrenaline? 

CORRECT ANSWER
Hormones
EDDIE SAYS
Hopefully, this didn't catch you out! There are many types of hormones and they all play different roles in the body. These ones are two of the most important so find out what you can about them.
  • Question 8

 

Thyroxine plays an important role in controlling our metabolic rate. The levels of thyroxine are maintained using a negative feedback cycle.

 

Fill in X and Y in the negative feedback cycle below.

 

Image of negative feedback cycle of thyroxine

CORRECT ANSWER

Column A

Column B

X
Pituitary Gland
Y
Thyroid Gland
EDDIE SAYS
Well done if you got this one correct - it is quite tricky to remember which way round these should go. To help you remember: Thyroid produces Thyroxine They both begin with a Thy! No easy way to remember the other one, but you can get it from a process of eliminating the other one! The pituitary gland produces TSH or thyroid-stimulating hormone.
  • Question 9

Adrenaline is released by the adrenal glands.

 

Complete the positive feedback loop by filling in X. 

 

Image of adrenaline feedback loop

CORRECT ANSWER
Fight or flight response
EDDIE SAYS
Adrenaline is most commonly associated with the fight or flight response. It's an example of a positive feedback loop as responses are magnified.
  • Question 10

 

The correct levels of thyroxine in the blood have to be maintained. This is an example of a negative feedback loop. 

 

Describe what's happening at A and B in the graph below.

 

Image of graph of thyroxine levels

CORRECT ANSWER
A: High thyroxine levels, TRH and TSH release inhibited
B: Thyroxine levels return to normal
EDDIE SAYS
If you study the graph carefully, you can see that at point A the thyroxine levels are high. This means that the body needs to bring this level down by inhibiting the release of TRH and TSH. Point B shows the thyroxine levels have returned to normal. A negative feedback cycle is where conditions return to normal after being either too high or too low.
  • Question 11

The sentences below describe homeostasis.

 

Place these sentences in order. 

CORRECT ANSWER
EDDIE SAYS
How did you do? If you found this hard, why not have a few tries at this activity to consolidate your knowledge of homeostasis and negative feedback. You've completed another activity - you're flying through these!
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