Homeostasis is a process that keeps the internal conditions stable inside our bodies. This includes changes in the external environment, such as going from hot to cold. It relates to several topics in the GCSE Biology curriculum, including enzymes, hormones, and the nervous system. Homeostasis keeps the body efficient by regulating our body temperature, water levels, and blood glucose.
If we didn't have this process, the systems in our bodies would quickly be affected. Enzymes would stop working, chemical reactions would change speed, and vital processes could fail. Homeostasis is always monitoring and adjusting the internal conditions using control systems to maintain optimum conditions.
This article will explain homeostasis, including how it works, why it matters, and key examples of the process. Quiz questions are included to test your understanding. It is suitable for all major exam boards, including AQA GCSE Biology, and can be used for GCSE combined science.
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What is Homeostasis?
Homeostasis is the regulation of the internal conditions of a cell or organism. The aim is to keep optimum conditions for internal functions, and this includes a response to internal and external changes.
There are three conditions controlled by this process:
- Body temperature - kept to approximately 37 degrees. It allows enzymes to work at their optimum.
- Blood glucose levels - the sugar level in the blood is maintained, so there's a constant supply of energy for respiration.
- Water levels - this is balanced to stop cells from overly gaining or losing water.
There is a particular target level for these conditions, which is called the set point. It's normal for there to be small ranges within an accepted range. If any one condition moves too far from the set point, the body will work to bring it back into range.
The processes in our bodies depend on stable conditions. Enzymes become less effective when the temperature is too low, while they denature (the molecular structure will change) if it is too high.
Homeostasis is automated and ongoing. The body is always tracking the internal conditions and adjusting when needed.
1
Which option isn't controlled by homeostasis?
Importance of Homeostasis
Cells and enzymes only work effectively in a narrow range of conditions. When the internal environment moves beyond this range, key biological processes can slow down or stop completely.
Enzymes are particularly vulnerable to change. There is an optimum temperature and pH for every enzyme. If the body temperature is too hot, enzymes will start to change and stop functioning. If the temperature drops too much, the enzyme activity slows down, reducing the rate of crucial reactions, such as breathing.
The glucose level needs to be stable in our blood. Glucose is needed for respiration, which releases energy for cells. If the sugar level falls, there won't be enough energy for important processes. If it's too high, this can damage cells and tissues over a sustained period of time.
Cells need the correct amount of water to keep their shape and functionality. If there's too much water, the cells may swell and burst. If there's not enough water, the cells can shrink and stop working.
2
Why does our body need to maintain a stable temperature?
The process - Homeostasis and response
Several stages detect changes and respond when needed. Their performance can be thought of like a control system that is always running to keep conditions within a certain range.
Stimulus
This is a change to the internal environment that moves a condition from the set point. For example, an increase in body temperature when exercising, or a rise in blood glucose after eating or drinking.
Stimuli can be from inside the body or due to external changes. These changes can affect the internal balance, and the body has to detect them quickly so the conditions don't stray too far from the set point.
Receptors
These are specialised cells that track changes in the internal environment. There are different types of receptors, and they respond to different stimuli. For example, thermoreceptors spot changes in temperature, while chemoreceptors track changes in chemical levels, like glucose or carbon dioxide.
Receptors are found in various parts of the body. This includes the skin, brain, spinal cord and organs. When a change is detected, receptors send signals to the coordination centre.
Coordination centre
This is where all the information is processed from receptors. It looks at the detected condition and compares it to the set point. It then decides what actions need to happen so the conditions return to the set point.
There are two main coordination centres:
- The brain is our nervous system, which has millions of neurons and uses electrical impulses to communicate.
- The pancreas is the hormonal system. It releases hormones into the bloodstream to control glucose.
Effectors
The effectors are muscles or glands. They act on signals from the coordination centre and are responsible for making the response that will bring the condition back within range.
For example, the muscles can contract to generate heat, such as shivering when it's cold. The glands can release substances, such as the sweat glands releasing sweat to regulate body temperature.
Response
The response is the action by the effectors to return the condition towards the set point. It isn't guaranteed to return the condition to normal immediately, but it reduces the difference in range. For example, insulin is released when the glucose levels in the blood are too high. If the glucose remains high, more is added incrementally until the level is approximately 4.0 to 5 mmol.
This is part of the negative feedback process, which reduces the original change. When the condition is in an acceptable range, the response is lowered or stopped completely.
3
Which stage in homeostasis corrects a change in the body?
Negative feedback with examples
This is the mechanism to reverse a condition change away from the set point. The aim is to keep internal conditions stable.
When a condition moves away from the set point, this is detected by the body and a response is triggered to reduce the difference. Eventually, the condition is brought back to the original level.
Let's say our body temperature rises above 37 degrees Celsius:
- The increase is detected by receptors.
- The coordination centre processes the information.
- Effectors increase the amount we sweat and widen our blood vessels.
- Heat is lost from the body, and our temperature returns to normal.
Similarly, if the temperature drops too low, our muscles will contract to cause shivering. The blood vessels will narrow to reduce heat loss, and the body temperature will start to rise.
Negative feedback aims to reverse the original change in condition, rather than continue it. These systems are constantly active and will adjust the strength of a response depending on how far the condition is from the set point. When the condition is back to a normal range, the response is reduced or stopped altogether to avoid overcorrection.
4
Why is negative feedback important in homeostasis?
Body temperature regulation
The temperature of our body needs to stay close to 37 degrees. Enzymes work best at this temperature. If the body temperature moves too far from this set point, enzyme activity is affected, and the key processes in the body will suffer.
The hypothalamus controls temperature regulation, which is the thermoregulatory centre in the brain. It is the coordination centre, receiving information from temperature receptors in the skin and the brain:
- Body temperature is high - the body works to lose heat. Sweating increases, which evaporates from the skin. Vasodilation also occurs, which is when the blood vessels widen near the skin. This increases blood flow and allows more heat to be lost.
- Body temperature is low - the body stores and creates heat. The person will shiver, which causes the muscles to contract rapidly, generating heat through respiration. Vasoconstriction also occurs, which is the opposite of vasodilation: the blood vessels narrow near the skin, reducing the loss of heat.
5
What can reduce body temperature?
Blood glucose regulation
There needs to be a certain level of glucose in the bloodstream to give energy to cells that they can use to release energy needed for respiration. The process is controlled by the pancreas, which is the coordination centre. It keeps track of the blood glucose levels, releasing hormones to adjust them when needed. This includes the hormone called insulin:
- Blood glucose is high - the sugar level in the blood rises after eating or drinking. The pancreas releases the hormone insulin, which causes glucose to move from the blood into cells. It also converts excess glucose into glycogen in the liver and muscles. These actions bring the glucose level in the blood back towards the set point.
- Blood glucose is low - this can happen between meals or during exercise, such as going for a run. The pancreas releases the hormone glucagon. This converts glycogen (excess glucose) to be converted back into glucose, which is then released into the bloodstream. The result is an increased blood glucose level.
This system operates using negative feedback. The release of insulin or glucagon is reduced when the blood glucose level is back to normal. A stable blood glucose level is essential. Without this control, complications can arise, such as diabetes, which means the body can't regulate glucose.
6
What hormone is released when the glucose level in the blood is too low?
Final thoughts - Control of Homeostasis
The homeostasis process keeps the body's internal condition stable, even if the external environment changes, such as getting warmer or colder. Keeping the internal conditions at a set point is crucial for our survival, due to enzyme activity and chemical reactions.
There are control systems that use receptors, coordination centres and effectors. They all work together using negative feedback to return conditions gradually back to their set points. This includes body temperature and blood glucose.
If you are interested in further reading, you can learn about the nervous system with this link from BBC Bitesize. You can also test yourself with past exam questions from Physics and Maths Tutor.
If you need help learning this topic, TeachTutti has top GCSE Biology tutors who can support you as you revise online or in-person. Every tutor has an enhanced DBS check and will tailor lessons to your specific needs.
