Thyroxine
Biology: AQA GCSE Higher, topic 5.3.3
Thyroxine
Thyroxine is the main hormone secreted (released) by the thyroid gland. It increases the basal (resting) metabolic rate.
Purpose
- Thyroxine is responsible for regulating the growth and brain development of young animals.
Regulation
- Production is regulated by a negative feedback loop. This allows the body to maintain a fairly constant concentration of thyroxine in the blood.
- When the concentration of thyroid hormones, such as thyroxine, in the blood is low, the production of thyroid-stimulating hormone (TSH) is increased. This stimulates the secretion of thyroxine by the thyroid gland.
- When the concentration of thyroid hormones in the blood is high, TSH production is decreased.
Test yourself on Thyroxine
Why is the secretion of thyroxine controlled by negative feedback?
What happens if there is too little thyroxine in the blood?
What happens if there is too much thyroxine in the blood?
What would you expect to be most affected in a young animal with very little thyroxine in its blood?
What can be concluded if the production of thyroid-stimulating hormone (TSH) is low