Not Rocket Surgery

Negative feedback is a naturally occurring / automatic off-switch in the body.

Image via Wikipedia

Imagine you are boiling water in a modern electric kettle.

• Your aim is to heat the water up to boiling temperature to, say, make a cup of tea.
• When you switch the kettle on, this has the effect of heating an element in the kettle and heat is gradually transferred to the water causing it to boil.
• If you keep the element on permanently, the water will gradually become steam, there will be no water left for your cup of tea and your will have wasted a lot of energy.
• Instead, as the water becomes steam, it passes through vents at the top of the kettle – the steam heats up a thermostat and when it reaches the set temperature, the kettle switches off.

This is negative feedback because the very water which you were heating, once at the required temperature, causes the heating process to switch off.

So, relating that to processes which occur in nature (of which there are many), here’s an example of biological negative feedback:

• If an animal’s blood glucose begins to rise, cells in the pancreas (called Beta Cells) detect this increase and release insulin.
• The effect of insulin is to allow glucose to be taken from the blood, into the cells, so that the cells can use it for energy.
• As the cells take up glucose, the glucose levels in the blood begin to fall.
• Falling levels of glucose are detected by the Beta Cells in the pancreas and – this is the Negative Feedback part – insulin release is switched off.
• This helps to prevent glucose levels falling to dangerously low levels.

Other examples of negative feedback include, temperature regulation (under central nervous influence), blood pressure control (by the Renin-Angiotensin-Aldosterone System), blood calcium control and many others.