Feedback Systems

Negative Feedback

The human body must maintain certain internal conditions in order to function correctly; this is called homeostasis.

Many bodily conditions are controlled by negative feedback cycles. They work by detecting and counteracting changes in bodily conditions, returning levels back to their optimum. This happens automatically in the body.

Effectors continue producing responses as long as they are stimulated by coordination centres which means it is common for the level to be increased/decreased too much. In these cases, negative feedback begins again in the opposite direction.

Effectors can produce nervous responses or hormonal responses.

Thyroxine

Thyroxine is a hormone that controls metabolism. It has many uses within the body such as regulating the speed of chemical reactions when at rest (basal metabolic rate) and controlling growth and development by stimulating protein synthesis.

Thyroxine levels are monitored and optimum levels are maintained using a negative feedback cycle, to keep the body functioning correctly.

Thyroid stimulating hormone (TSH) is released from the pituitary gland and stimulates the thyroid gland to release thyroxine. 

• When thyroxine levels are too high, the secretion of TSH is inhibited, subsequently reducing the amount of thyroxine released from the thyroid gland. This allows thyroxine levels to fall back to the normal amount. 
• When thyroxine levels become too low, the secretion of TSH is increased, increasing the amount of thyroxine released from the thyroid gland.

Adrenaline

In scary and stressful situations, the hormone adrenaline is released which prepares the body for ‘fight or flight‘.

Fear and stress are detected by the brain which sends nervous impulses to the adrenal glands which start secreting adrenaline. 

Adrenaline triggers systems that will increase the delivery of oxygen and glucose to the brain and muscles, e.g. increasing heart rate, increasing breathing rate, increasing break down of glycogen. This prepares the body so it is able to respond quickly in dangerous situations.