Homeostasis

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1

Homeostasis

The body’s ability to detect change, activate mechanisms that oppose it, and thereby maintain relatively stable internal conditions.

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Dynamic Equilibrium

State of the body fluctuates within limited range around a set point

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The changes in our environmental conditions are called ______ because their values are not constant.

Variables

(i.e. hot or cold outdoor temp)

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Control Center

The part of the feedback mechanism that:

  • Receives and processes information
  • Relates it to other information
  • Makes a decision of action to be carried out by the effector.
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Receptor

A structure, molecule or cell that detects a stimulus (or change in body variable)

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Effector

The organ that carries out a response that changes the value of the variable

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Set point

Ideal normal value of body temperature.

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Negative feedback

  • Maintains homeostasis.
  • Response to the original stimulus decreases.
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Positive Feedback

  • The response to the original stimulus INCREASES
  • Mechanism that represents a cycle where physiological change leads to an even greater change in the same direction
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Positive Feedback Example

Birth:

  1. Head of fetus pushes againts cervix
  2. Nerve impulses from cervix transmitted to brain
  3. Brain stimulates pituitary gland to secrete oxytocin.
  4. Oxytocin stimulates uterine contractions and pushes fetus towards cervix.
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Harmful Positive Feedback

Fever > 104°F

  • Metabolic rate increases
  • Body produces heat even faster
  • Body temperature continues to rise
  • Further increasing metabolic rate
  • Cycle continues to reinforce itself
  • Becomes fatal at 113°F