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Adrenaline And Thyroxine (Higher Tier Only)

Laura Armstrong & Joe Wolfensohn

Teachers

Laura Armstrong Joe Wolfensohn

Contents

Adrenaline and Thyroxine

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Recall Questions

This topic requires prior knowledge of the endocrine system and negative feedback.

What is negative feedback?

A control mechanism where a change from the normal level triggers a response to reverse the change

Which gland produces adrenaline?

The adrenal glands

What hormone is released by the thyroid gland?

Thyroxine

Topic Explainer Video

Check out this @JoeDoesBiology video that explains adrenaline and thyroxine, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!

Adrenaline and Thyroxine

What is the Role of Adrenaline?

  • Adrenaline is a hormone produced by the adrenal glands in response to fear or stress.
  • It prepares the body for ‘fight or flight’:
    • Increases heart rate and breathing rate.
    • Boosts delivery of oxygen and glucose to muscles and brain.
  • This allows rapid energy release for action.
    • It also increases blood pressure, causes pupils to dilate and leads to the breakdown of glycogen into glucose to increase blood glucose concentration.

Adrenaline is not controlled by negative feedback. It is a short-term, emergency hormone.

What is the Role of Thyroxine?

  • Thyroxine is released by the thyroid gland.
  • It controls the basal metabolic rate (rate of chemical reactions in the body at rest)

  • Thyroxine levels are controlled by negative feedback.

If thyroxine levels fall:

  • The pituitary gland releases TSH (Thyroid Stimulating Hormone).
  • TSH stimulates the thyroid gland to make more thyroxine.
  • This increases metabolic rate and therefore, the rate of respiration.
  • When thyroxine levels rise back to normal, TSH production is reduced from the pituitary gland.
  • The thyroid gland makes less thyroxine.
  • Thyroxine levels return to normal and metabolic rate is stable.

 

Key Terms

  • Adrenaline: Emergency hormone for fight or flight.
  • Thyroxine: Hormone that regulates metabolism.
  • Basal metabolic rate: The rate of chemical reactions in the body at rest.
  • TSH: Hormone from the pituitary gland that stimulates thyroxine release from the thyroid gland.
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Exam Tip

Don’t mix up the roles of adrenaline (short-term emergency response) and thyroxine (long-term metabolic control). Only thyroxine is regulated by negative feedback.

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Practice Question

Explain how the thyroid gland controls the response to a decrease in body temperature by negative feedback. (3)

Model Answer:

  • Decrease in body temperature stimulates the thyroid gland to produce more thyroxine.
  • increased / more thyroxine raises metabolic rate.
  • which increases rate of respiration, which increases body temperature (as more heat energy is released).

More Practice

Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!

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