Download - Principles of Control System HB 14 Sep 2010
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Principles of control system
Dr. Isabel HwangTeaching and Learning Unit
School of Biomedical Sciences,Faculty of Medicine, CUHK
14 Sep 2010
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Email: [email protected] ID: [email protected]: Room 410C, BMSB, School of Biomedical Sciences, Faculty of MedicinePhone no: 2609 6795
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LECTURE OUTLINEDefinition of homeostasisComponents of a control systemFeedback control mechanisms 1.positive 2.negativeFeedforward mechanism
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Homeostasis
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Maintenance of a stable internal environment (dynamic constancy ) is called homeostasis.Homeostasis is regulated through control systems which have receptors 受容器 (sensors), a set point 設定點, integrating center 整合中心 and effectors 效應器 in common.
Examples include:a. Homeostatic mechanisms regulate body
temperature (thermoregulation) in a manner similar to the functioning of a home heating thermostat.
b. Another homeostatic mechanism employs pressure-sensitive receptors to regulate blood pressure.
Homeostasis 體內平衡
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Externalenvironment
Homeostaticmechanisms
Internalenvironment
Smallfluctuations
Largefluctuations
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Homeostasis continued
No physiological function is constant for very long, which is why we call them “variables”Normally, blood sugar (glucose) remains at fairly steady and predictable levels in any healthy individualAfter a meal the level of glucose in your blood can increase quicklyIf you skip a meal, your blood sugar level may drop slightlyHomeostatic mechanisms restore blood glucose to normal levels in the blood
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Homeostasis continued
Parameters are stabilized above and below a physiological set point
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By feedback mechanismsfundamental feature of homeostasistwo types: 1. Negative feedback (most
common) 負回饋
2. Positive feedback 正回饋
Methods of Homeostatic Regulation
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Negative Feedbackmost common the response of the effector opposesor eliminates the original stimulusrequires frequent monitoring and adjustmentdecrease in body temperature leads to responses that increase body temperaturemay occur at organ, cellular or molecular levelother e.g. blood pressure, blood sugar
Methods of Homeostatic Regulation
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Negative feedback loops
detects deviation from set point
Sensor/ receptor:
produces response
Integrating center:
determines response
Effector:
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Negative feedbackThe primary (major)mechanism for maintaining homeostasis
Has two components: sensor control center
The output of the system dampens the original stimulus
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Negative feedbackcontrol
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An example of negative feedback:
Body temperature:
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Thermoregulation
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Hormonal control of blood glucose
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Regulation of blood pressure
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A mechanism for increasing the change of the internal environment in one directionIs relatively less common because the response of the effector enhances or exaggerates the original stimulus The change that occurs reinforces the direction of the changeE.g. blood clotting,
labor contraction
Positive feedback
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The body maintains homeostasis using both negative and positive feedback control mechanisms
Most of the body's homeostatic controls are negative feedback mechanisms.
Each individual uses homeostatic mechanisms to keep body levels within a normal range; normal ranges can vary from one individual to the next.
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Human’s body begins preparing for a change in some variable before it occursAnticipatorySpeeds up homeostatic responses and minimizes deviations from the set pointMany result from or are modified by learning
Feedforward regulation
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Feedforward regulationFeedforward ≠ Feedback
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Feedforward control of breathing rate in horses trained for racing
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Homeostatic imbalances
Lack of homeostasis results in disease
and/or death
Decline in homeostasis normal aging process
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The end.