AchievedDescribing:
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MeritExplaining:
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ExcellenceLinking:
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Biological ideas related to the control system includes the:
- purpose of the system
- components of the system
- mechanism of the system (how it responds to the normal range of environmental fluctuations, interaction and feedback mechanisms between parts of the system)
- potential effect of disruption to the system by internal or external influences
Homeostasis basics
Homeostasis is a term used for 'maintaining a constant internal environment' - for example, staying the right temperature even when it is cold outside.
3 System components are needed for homeostasis
and 2 communication systems are needed for the components to 'talk' to each other
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Component 1
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Component 2
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Component 3
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Comm. System 1
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Comm. System 2
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Receptor(s)
- detects a change in the environment (stimuli)
- i.e. thermoreceptors in the skin - these receptors can detect a change in temperature
Control centre
- processes the message sent from the receptors and coordinates a response
- i.e. the hypothalamus in the brain - this is the control centre for the release of hormones into the blood
Effector(s)
- produces an appropriate response to the stimuli
- i.e. glands and muscles - for example, our body may start to shiver when we detect cold temperatures
The nervous systemThe nervous system is a network of nerve cells which transmit information to each other using electrochemical impulses. When one receives an impulse, it sends it on to the next cell. The electrochemical impulses are called action potentials. They travel very fast throughout the body. They will travel from the nerve receptor cells (where they can detect a change in environment) through to the spinal cord and up to the brain.
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The endocrine systemThe endocrine system is the system in the body where hormones are created and released. Hormones are really important chemical messengers in the body and travel through the blood stream, rather via neurons. This means they take a little longer to communicate messages between different parts of the body.
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The nervous system and endocrine system work closely together - often the nerves pick up the stimuli and transmit that message to the brain via. the nervous system. The hypothalamus (a part of the brain - a control centre) can translate that electrochemical message and respond by releasing neurohormones from the pituitary gland, located nearby, into the bloodstream (if releasing hormones is an appropriate response). The hypothalamus, and other parts of the brain, can also transfer the message via nerves to a different gland in the body (i.e. pancreas) from which different hormones can be released, or to specific muscle cells which can then perform an appropriate response.
Nervous vs. hormonal control
Nervous control |
Hormonal control |
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Communication |
Electrochemical impulses between nerve cells - called synapses |
Hormones released into the bloodstream |
Action |
Tells muscles to contract, tells glands to secrete |
Causes a change in the metabolic activity (stops/slows/speeds up reactions) |
Speed |
Within a few seconds - very fast response |
Within minutes, hours or longer - quite a slow response |
Duration |
Short term, can be reversed |
Longer lasting effects |
Target pathway |
Message reaches specific cells through the nerves - message directly sent from one place to another |
Hormones are released into the blood stream so will go wherever the blood goes - broadcast to target cells everywhere |
Feedback loops
Think about this: once we cool down from being out in the sun, our body doesn't continue to keep cooling itself down... There will be a time when the response to the stimuli (such as warm temperatures) will stop. This can only happen if a signal is sent - a feedback loop.
Feedback can be either:
Feedback can be either:
NegativeWhen a stimulus takes the individual away from their steady state (i.e. they get too hot), the response is for the body to cool down. When the body is back at a 'steady' temperature, this acts as a signal for the body to stop cooling itself down. The feedback loop ends when the body returns to its steady state.
Basically, a negative feedback loop aims to create a response that reduces or stops the size/effect of the stimulus. This is really common in the human body. When discussing negative feedback for the two examples below, always remember to close the loop.
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PositiveWhen a stimulus takes the individual away from their steady state (i.e. they encounter a pathogen), the response is to amplify a physiological response in order to achieve some sort of result (i.e. increasing body temp so you get a fever). The feedback loop ends when a natural solution, such as the destruction of the pathogen, is reached. When this happens, the body will naturally return to homeostasis.
Basically, a positive feedback loop exaggerates the body's response to a stimulus until a particular result has been achieved. This is really uncommon in the human body. |
We will focus on two aspects of homeostasis in our bodies - maintaining an appropriate internal temperature and ensuring the level of glucose molecules in our blood is not too high or low
Normal body temperature in humans is 37°C - this is the optimum temperature for enzymes to work efficiently. Enzymes are involved in all the reactions that occur to keep our metabolism running - they are involved in digestion, respiration, etc. If they don't work, our body won't work! Temperature needs to be regulated so we don't become too hot (which would denature our enzymes) or too cold (which would mean they don't work fast enough).
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