Negative feedback is a type of regulatory system that helps to maintain conditions in the body within an ideal range. Some conditions that are kept constant in humans are:
Most control systems use negative feedback to maintain homeostasis. A negative feedback mechanism detects when conditions rise above or fall below the ideal range. This triggers a response which brings them back to normal levels.
The adrenal glands are located just above the kidneys. During times of fear or stress, the hypothalamus triggers the adrenal glands to produce the hormone adrenaline (and cortisol). This prepares the body for ‘flight or fight’. Adrenaline is not controlled by negative feedback
Adrenaline increases the heart rate. As the heart is beating faster, more oxygen and glucose are delivered to the brain and muscles through the blood. Oxygen and glucose are required for aerobic respiration.
Some other effects are:
These responses help the body to respond quickly when it is essential.
Thyroxine is a hormone in the body that is secreted by the thyroid gland, which is located in the neck. Thyroxine has two main roles in the body:
Unlike adrenaline, thyroxine is controlled by negative feedback:
1. When the thyroxine levels fall too low, the hypothalamus releases the hormone TRH
2. TRH acts on the pituitary gland, causing it to release the hormone TSH
3. TSH stimulates the thyroid gland to release more thyroxine
4. At normal thyroxine levels, the release of TRH from the hypothalamus is inhibited
5. This inhibits the release of TSH, so thyroxine levels will be maintained