Endocrine Glands (More Detail)


Thyroid Gland (Thyroxine)

Thyroxine is the main hormone released by the thyroid gland. Increases the basal (resting) metabolic rate. 

Responsible for regulating the growth and brain development of young animals.

Production of thyroxine is regulated by a negative feedback loop.

Levels are too low:

  • The production of TSH is increased. This stiumaltes the release of thyroxine 

Levels are too high: 

  • The production of TSH is decreased. This relaxes the stimulation of the release of thyroxine

(TSH = thyroid-stimulating hormone)

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Adrenal Glands (Adrenaline)

Adreneline is a hormone released by adrenal glands. It has different functions/ purposes. 


  • Enlargers the air passages of the lungs and alters metabolism to boost the delivery of oxygen and glucose to the brain and muscles 

'Fight' or 'Flight'

  • When in a time of fear/ stress adrenaline prepares the body to move and think quickly in response to danger

Heart rate and blood pressure 

  • Increases the heart rate and blood pressure. It also dilates the pupils in our eyes.
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Blood Glucose

The optimal blood glucose level for humans is 6-8 mmol/ dm³. 

Too little glucose:

  • Cannot produce enough energy for the organism/ cells (due to no energy released due to little respiration) 

Too much glucose:

  • Can have a negative impact on osmosis (movement of water between cells) by affecting concentration gradients
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