principles of control system hb 14 sep 2010

Principles of control system

Dr. Isabel HwangTeaching and Learning Unit

School of Biomedical Sciences,Faculty of Medicine, CUHK

14 Sep 2010

Email: isabelss@cuhk.edu.hkMsn ID: isabelhwang@hotmail.comOffice: 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

Homeostasis

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

Externalenvironment

Homeostaticmechanisms

Internalenvironment

Smallfluctuations

Largefluctuations

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

Homeostasis continued

Parameters are stabilized above and below a physiological set point

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

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

Negative feedback loops

detects deviation from set point

Sensor/ receptor:

produces response

Integrating center:

determines response

Effector:

Negative feedbackThe primary (major)mechanism for maintaining homeostasis

Has two components: sensor control center

The output of the system dampens the original stimulus

Negative feedbackcontrol

An example of negative feedback:

Body temperature:

Thermoregulation

Hormonal control of blood glucose

Regulation of blood pressure

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

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.

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

Feedforward regulationFeedforward ≠ Feedback

Feedforward control of breathing rate in horses trained for racing

Homeostatic imbalances

Lack of homeostasis results in disease

and/or death

Decline in homeostasis normal aging process

The end.