5.3.7 - Negative Feedback

What is negative feedback?

A type of control where the body responds to an increase or decrease in a factor by returning it to the optimum level.

What is thyroxine?

• A hormone released by the thyroid gland.

• Its release is triggered by the thyroid stimulating hormone (TSH).

• Thyroxine controls the body’s metabolic rate, growth, and development.

How is the release of thyroxine controlled by negative feedback?

• Levels of blood thyroxine falls - detected by receptors in the brain.

• Pituitary gland releases more TSH.

• More thyroxine produced and released by the thyroid gland.

• Blood thyroxine level returns to normal.

What is adrenaline?

A hormone secreted by the adrenal gland in times of stress. It is responsible for the “fight or flight” response.

What are the effects of adrenaline?

• Increase in heart and breathing rate - delivers oxygen and glucose to the body.

• Stored glycogen converted to glucose.

• Dilation of pupils.

• Increased mental awareness.

• Blood diverted away from digestive system to muscles.