What is an analogy?
The body
Before birth

Homeostasis is the name given to all the processes in the body which maintain a balanced internal environment so that all the cells can function normally. There is evidence that animal species evolved in the oceans before making the transition onto land about 400 million years ago, and to this day the internal environments of land animals resemble the wet and salty ocean environment from which they emerged.

Homeostasis is a dynamic equilibrium in the sense that it is influenced by our level of activity. For example, when we exercise our heart has to work harder to keep the muscles well supplied. However, when the changes occur they do so within closely controlled limits. This close control is essential to maintain good health because  many essential chemical events can only occur if the conditions are correct.

Key variables that require homeostatic control include body temperature, blood pressure, sugar levels in the blood, fluid and electrolyte levels, and the pH (acidity/alkalinity) of body fluids. If one or more homeostatic processes fails to maintain a suitable balance, then illness or even death may result.

In essence, homeostasis is about control systems. Some of the body’s control systems work very quickly, while others work over much longer time scales. Most of the control systems work in the following way:


a sensor monitors the output of a particular system


the level registered by the sensor is compared with a preset level


if the registered level is too high, the system is turned down


if the registered level is too low, the system is turned up

Because of this reciprocal relationship between the system and the regulator, the process is called ‘negative feedback’. This process of monitoring and adjustment continues to keep the value of the variable at the required level. Consider for example the level of blood sugar. The level of glucose in the blood rises after a meal rich in carbohydrates. This triggers the release of a pancreatic hormone  called insulin which enables cells around the body to take in glucose and use it as a source of energy. Any excess glucose can be taken in by liver and muscle cells and stored as glycogen. When blood glucose levels fall, another pancreatic hormone called glucagon raises blood glucose by mobilising the stored glycogen.

Our ability to regulate our internal environment changes during our lifespan. A young baby cannot shiver to generate more heat if it gets cold - however, it has a special tissue called brown fat that can generate heat. As we age, our body systems become less efficient and our internal environment becomes more easily disturbed.

All the homeostatic processes are closely interlinked and interdependent, and every system and every cell has some part to play in homeostasis. Homeostasis is a central concept in healthcare practice, so it is a worthwhile subject to study.

If you would like to see some questions and answers about homeostasis, please click here.

horizontal rule

Home What is an analogy? The body Before birth