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BTEC applied science unit 9B- homeostatic control of body systems
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Aliya HussainUnit 9.2: homeostatic control of body systems
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,Aliya Hussain
P2: Describe how homeostatic mechanisms maintain normal functions
Homeostasis the process by which the body maintains a constant internal
environment. This includes things such as body temperature, blood glucose
levels and pH levels.
The body's requirement to maintain homeostasis is the constant monitoring of
internal factors and their changes in response to external factors. This constant
monitoring is done through two processes:
- Positive feedback
- Negative feedback
Feedback mechanism
The feedback mechanism is the physiological regulatory system in a living body
that works to return the body to the normal internal state. ………
The Thermostat Analogy
The thermostat analogy is an example of a feedback mechanism. When the
temperature of the room falls the thermostat detects the change and switches
the radiator on so that the temperature of the room increases. When the room
gets too warm, the thermostat detects the increase in the temperature and
switches the radiator off to allow the temperature of the room to decrease. In
conclusion the radiators are switched an or off depending on the temperature
of the room detected by the thermostat.
Negative feedback
Negative feedback brings a system back to its level of normal functioning.
Adjustments of blood pressure, metabolism, osmoregulation, and body
temperature are all negative feedback.
Maintenance of homeostasis usually involves negative feedback loops. These
loops act to oppose the stimulus, or cue, that triggers them. It responds when
conditions change from the ideal or set point and returns them to their set
point. The negative feedback follows the thermostat analogy.
All negative feedback systems have similar components:
-An output (the factor that needs to be controlled, such as temperature, blood
pH, glucose)
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, Aliya Hussain
-A set point, which is the standard for the factor.
Detectors (sensory receptors) monitor the output and coordinators/ regulators
compare the actual output with the set point and send out an error signal
when they output falls outside the set point range.
[figure 1]
Positive feedback
Positive feedback involves a response that reinforces the change detected. A
change is detected by a receptor and an effector is activated to induce the
same effect; this promotes further change. Positive feedback loops will
continue to increase the initial change until the stimulus is removed.
Positive feedback can be harmful because it can create unstable conditions,
however, in some circumstances positive feedback is useful. An example of a
useful positive feedback is the release of oxytocin from the posterior pituitary
gland during labor. Oxytocin stimulates the muscle contractions that push the
baby through the birth canal. The release of oxytocin result in stronger or
augmented contractions during labor. The contractions intensify and increase
until the baby is outside the birth canal. When the stimulus to the pressure
receptors ends, oxytocin production stops, and labor contractions cease.
Positive feedback mechanisms control self-perpetuating events that can be out
of control and do not require continuous adjustment.
[Figure 2]
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