Homeostasis, Control Systems - Lecture 2

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D. Control systems--systems designed to maintain homeostasis

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Organism has many interdependencies among organs and tissues.

What is the basis for maintaining each system at the proper rate of operation.  In general terms, A CONTROL SYSTEM REGULATES SOMETHING.   To understand how different systems work, analyze components of a general system.   There are changes- body is dynamic - BP., temp., etc.

Components of generalized circuit -- from physics/engineering

1. feedback transducer: transduces or changes one form of energy to another: encodes information about where system actually is so that the controller can read it. i.e. change heat to electrical voltage.

2. reference point: the desired level of the controlled process-where the system should be.

3. controller: master area which directs or controls the system: compares the reference input to information relayed by the feedback transducer

4. error signal: if difference exists between ref. input and transducer output.

5. activator: produces a response or output when turned on by the controller.

6. Controlled output, response of the activator.

Analogy

Physical: keeping house warm in winter

also, eye sight; eyes-brain-too dark-dilate pupil

feedback transducer--thermometer

reference input--thermostat setting

controller--thermostat mechanism

error signal if temp. less than setting--trip switch to furnace

activator--furnace

controlled output--heat

When heat output causes room temp to rise above temp setting on thermostat, error signal is shut off by thermostat and furnace turns off-----body temp-hypothalamus.

Body systems: what is regulated - body temp, plasma (glucose), plasma (Na), arterial blood pressure, various hormones, etc.

 

--Baroreceptor

--medulla-increase HR, decrease HR

--blood vessels, heart

E. Types of feedback:

Negative system--stimulus causes a response which works to reduce the stimulus. i.e. air cooling down--heat generated to warm air back up, most physiological systems operate on negative feedback system. i.e. blood pressure

Positive feedback: stimulus causes a response which increases the stimulus, i.e. if decrease temp. caused mechanism to open window; as windows open, cool air moves in--further decreases in temp.--causes more windows to open. This system pushes the conditions to an extreme.

Physiological example--Na+ channels during action potential formation; loss of blood - causing irreversible shock--capillary pressure increases, causing further loss of blood volume; increased body temp when in desert--lose water; sweat-lose water.

Homeostasis-process of keeping body around desired level for many different characteristics: a tendency toward maintenance of a relatively stable internal environment in the face of stress from the external and internal environments

When system fails - pathophysiology - abnormal suffering

abnormal functioning of body - disease; if severe - death.

REVIEW QUESTIONS

1. Which of the following is an example of negative feedback?
   1. The heart rate increases when there is a decrease in blood pressure.
   2. You began to sweat when it's cold outside.
   3. Your body craves sweeps when your glucose levels are elevated.
   4. Your respiration increases when you are resting.
2. Which of the following factors is not homeostatically controlled?
   1. The blood pH.
   2. Body temperature.
   3. Nitrogen levels.
   4. Oxygen and carbon dioxide levels
   5. Glucose concentration.
3. What type of control is responsible for maintaining body temperature relatively constant?
   1. Negative feedback.
   2. Homeostatic feedback.
   3. Positive feedback.
   4. Biofeedback.
   5. Nervous feedback.
4. What feedback mechanism is designed so that the output works to increase the input?
   1. Negative feedback.
   2. Homeostatic feedback.
   3. Positive feedback.
   4. Biofeedback.
   5. Nervous feedback.
5. The heart is an example of a
   1. receptor
   2. controller
   3. activator
   4. controlled output
   5. transducer

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