Keeping Healthy - Keeping a Healthy Balance

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Our bodies need to control things like body temperature and water level to keep them constant. The process of keeping things the same is called homeostasis.


Cells in the body need certain conditions to work properly. Homeostasis is how the body keeps internal conditions the same. Two examples of things that the body keeps the same are: body temperature at 37 degrees celcius and the amount of water inside our body. Keeping these two the same is not always easy when the outside environment is changing constantly. But it is important so that all our cells function properly. Strenuous exercise, or living in a hot or cold environment, affect our body temperature and water balance. 

Body Systems

We have control systems in our bodies to maintain a steady state. First we need receptors to detect when things such as temperature change. Then we need a processing centre to recieve this information and coordinate our response. 


The blood in veins is under lower pressure than the blood in the arteries. The veins have: thin walls, thin layers of muscle and elastic fibres. Finally, we need effectors to produce a response that ensures our body temperature stays at 37 degrees celcius. 

Negative Feedback - Higher Tier

Negative feedback ensures that, in any control system, changes are reversed and returned back to the set level. For example, negative feedback keeps our body temperature at a constant 37°C. If we get too hot, blood vessels in our skin become larger and we lose heat and cool down. If we get too cold blood vessels in our skin become smaller, we lose less heat and our body warms up. Negative feedback  makes sure this happens.The other factors also controlled in the body by negative feedback are: blood oxygen levels and salt levels.

Water Balance

The kidneys maintain our body's water balance by controlling the water concentration of blood plasma. The kidneys also control salt levels and the excretion of urea. Water that is not put back into the


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