Negative Feedback (AQA GCSE Biology): Revision Note

Negative feedback mechanisms in homeostasis help to maintain conditions in the body within an optimal narrow range; any movement away from ideal conditions results in changes occurring which bring them back

This involves detecting that the level of a substance or a condition has gone above or below normal levels, which triggers a response to bring the level back to normal again

Blood glucose level and core body temperature control are examples of negative feedback

Adrenaline is produced by the adrenal glands in times of fear or stress

• The adrenal glands are located just above the kidneys

In response to stressful or scary situations, the brain triggers the release of adrenaline from the adrenal glands

Adrenaline increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’

• Increased glucose and oxygen are needed by the cells for respiration to release energy; the delivery of more enables more energy to be released (to fuel the muscles to move/run away for example!)

Thyroxine is secreted into the blood by the thyroid gland

Thyroxine is involved with:

• stimulation of basal metabolic rate (BMR) – the rate of the chemical reactions in cells at rest; more thyroxine means more respiration, which releases more energy (some as heat), so thyroxine can raise body temperature

• control of growth and development

Thyroxine levels in the blood are also regulated by negative feedback

• If the level of thyroxine falls below a normal level, the pituitary gland releases TSH (thyroid-stimulating hormone); this increases release of thyroxine from the thyroid gland

• If the level of thyroxine is normal, or too high, the release of TSH is inhibited, reducing thyroxine production