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GCSE biology notes: Introduction to Homeostasis - negative feedback mechanisms

Introduction to HOMEOSTASIS

Doc Brown's Biology Revision Notes

Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent

1. What is homeostasis? What is its function?

 Negative feedback systems explained

 Homeostasis is the maintenance of a stable and constant internal environment in an organism.

 Homeostasis is crucial to the regulation of an internal environments and enables organisms to adapt to change, both internally and externally. Internal temperature, blood sugar levels, water level and osmotic balance are regulated by a number of organs and systems working together.



(a) Homeostasis

The conditions inside your body need to be kept as steady as possible even if the external conditions change.

This 'steadiness' or 'regulation' of the 'right conditions' is vitally important for your cells to function properly eg the action of enzymes which control most of your bodies chemistry.

Homeostasis is how the conditions inside the body are regulated to maintain a stable internal environment in response to changes in both internal and external conditions and usually involve a negative feedback system.

Your body also needs to monitor and balance material entering your body e.g food or oxygen and output materials e.g. waste products like urine or carbon dioxide.

Your body has numerous automatic control systems that help regulate your internal environment.

These include nerve responses and hormone response communication systems.

The body controls itself by means of negative feedback systems which constantly help keep conditions right for healthy sustainable life for what you might call 'normal conditions'.

Basically if something in the changes beyond a certain limit e.g. above or below a normal level, then the change is detected and the body automatically responds to balance things up again i.e. restore the of concentration of a substance in the bloodstream, body temperature, pH or water content to 'normal'.

Cells in the body can only survive within narrow physical and chemical limits.

They require a constant temperature and pH as well as a constant supply of dissolved food and water to function properly, including the right conditions for enzymes to perform their multiple catalytic functions.

This is why the body requires control systems that constantly monitor and adjust the composition of the blood.

It is bad for your health if conditions vary too much from 'normal'.

These control systems include receptors which sense changes and effectors that bring about changes.

Within these limits your body is as healthy as it can be!

For particular examples of homeostasis see:

Homeostasis - control of blood sugar level - insulin - diabetes  gcse biology revision notes

Homeostasis - water control, urea and kidney function  gcse biology revision notes

Homeostasis - thermoregulation, control of temperature  gcse biology revision notes

See also Hormone system - Introduction to the endocrine system - role of thyroxine  gcse biology


(b) How do negative feedback systems work?

There are many automatic control systems in your body that control and regulate your internal environment

e.g. the nervous system, hormone molecule communication.

Other control systems 'monitor' things such as your body temperature, water content and blood glucose levels.

The table below illustrates the general principles of maintaining the ideal 'level' of something e.g. temperature, pH, carbon dioxide, blood glucose, and water via three 'components' working in conjunction with one another to keep conditions steady.

All your automatic control systems consist of three components which work together to maintain you in a steady condition:

receptor cells which sense the state of the level of something changing in the environment and produce a stimulus,

coordination centre cells in the brain, spinal cord and pancreas, that receive and process information the receptors,

and effector cells that produce the response from e.g. muscles or glands secreting hormones.

Your automatic control systems keep your internal environment stable by means of a negative feedback mechanism so that the functions of the three sets of cells are all co-ordinated.

If your body detects a significant change from 'normal', an appropriate response is triggered.

This is outlined below and the word 'level' means the level of anything being controlled e.g. temperature, pH, blood sugar, water contents.

A general description of a body's homeostasis negative feedback system

The negative feedback in action for a 'level' too high The negative feedback in action for a 'level' too low
1. Receptor detects a stimulus that a level is too high 1. Receptor detects a stimulus that a level is too low
2. The coordination centre receives and processes the stimulus information and then organises a response by the effectors. 2. The coordination centre receives and processes the stimulus information and then organises a response by the effectors.
3. The effector produces a response which counteracts the change and restores the optimum level by reducing the level back to the required optimum level. 3. The effector produces a response which counteracts the change and restores the optimum level by increasing the level back to the required optimum level.
4. The effector will carry on producing the 'reducing' response as long as the coordination centre is stimulated by the receptors. 4. The effector will carry on producing the 'increasing' response as long as the coordination centre is stimulated by the receptors.
5. The effector response might be more than required, and the level becomes too low, if too far below the 'ideal', the receptors will detect this, and the negative feedback will stimulate the effectors to increase the level (1. - 3. on the right). 5. The effector response might be more than required, and the level becomes too high, if too far above the 'ideal' the receptors will detect this and the negative feedback will stimulate the effectors to decrease the level (1. - 3. on the left).
This is all automatically done by the organism's complex control systems and enables the organism e.g. your body, to maintain as near as possible the 'ideal' conditions for life!

Note: The coordination centre = control centre, just different phrases meaning the same thing!

This negative feedback detection system process is continuous so that there is always a small fluctuation from the 'NORMAL', illustrated by the graph below (green line ~normal).

The graphs shows the decrease and increase of a 'level' as the negative feedback system clicks into action.

Our negative feedback systems work well if external or internal changes are small, i.e. within certain limits, BUT, if the environment (ambient conditions) change too much, then our body might not be able to counteract the enforced change.


 

Homeostasis notes index:

Homeostasis - introduction to how it functions (negative feedback systems explained) gcse biology revision notes

Homeostasis - control of blood sugar level - insulin and diabetes gcse biology revision notes

Homeostasis - osmoregulation, ADH, water control, urea and ion concentrations and kidney function, dialysis

Homeostasis - thermoregulation, control of temperature gcse biology revision notes

and also Hormone systems - Introduction to the endocrine system - action of thyroxine hormone gcse biology revision


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General HUMAN BIOLOGY revision notes

Introduction to the organisation of cells => tissues => organs => organ systems (e.g. in humans)

Examples of surfaces for the exchange of substances in animal organisms   gcse biology revision notes

See also Enzymes - section on digestion and synthesis  gcse biology revision notes

The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

The brain - what the different parts do and the dangers if damaged gcse biology revision notes

An introduction to the nervous system including the reflex arc  gcse biology revision notes

Hormone systems - Introduction to the endocrine system - adrenaline & thyroxine hormones  gcse biology revision

Hormone systems - menstrual cycle, contraception, fertility treatments  gcse biology revision notes

Respiration - aerobic and anaerobic in plants and animals.  gcse biology revision notes

Keeping healthy - communicable diseases - pathogen infections   gcse biology revision notes

Keeping healthy - non-communicable diseases - risk factors for e.g. cancers   gcse biology revision notes

Keeping healthy - diet and exercise  gcse biology revision notes

Keeping healthy - defence against pathogens, infectious diseases, vaccination, drugs, monoclonal antibodies

See also Culturing microorganisms like bacteria - testing antibiotics/antiseptics  gcse biology revision

Food tests for reducing sugars, starch, proteins and lipids  gcse biology revision notes

The eye - structure and function - correction of vision defects  gcse biology revision notes

Optics - lens types (convex, concave, uses), experiments, ray diagrams, correction of eye defects (gcse physics)


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