Homeostasis

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Homeostasis

• Chapter 1
• Mr. Knowles
• Anatomy and Physiology
• Liberty Senior High School

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Homeostasis is a balancing act!
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Homeostasis

• Homeo- same.
• -stasis- standing or status.
• To maintain a relatively constant internal
  environment.
• External environment has many variables-temp.,
  pH, amount of energy, etc.

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What is a stimulus and a response?

• Stimulus- an environmental change that signals
  the body in some way.
• Response- the change in cellular activity the
  body makes in order to maintain homeostasis.

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Homeostasis is a Balancing Act!

• Chemical reactions within cells work most
  effectively within a certain range of conditions
  (temp., pH, salt, energy).
• Organ systems work together to maintain this
  stable internal environment.

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Homeostatic Regulation

• Two Mechanisms
• 1. Autoregulation- activities of a cell, tissue
  or organ change automatically when faced with
  environmental variation.
• Ex. Cells in a certain tissue need more O2.
  Cells?release chemicals?dilate (open) blood
  vessels nearby?local cells receive more O2 .
  Only localized changes.

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Homeostatic Regulation

• Two Mechanisms
• 2. Extrinsic Regulation-activities of several
  systems, such as the nervous and endocrine, work
  together to adjust or change the internal
  environment.
• Ex. Touching a hot stove ?nervous system
  responds?processes information?muscle contraction
  .
• Ex. Endocrine system? releases chemical
  messengers (hormones) ? affect many systems for a
  long period, last for hours, days.

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Homeostasis Has Three Parts

• Receptor- a sensor that is sensitive to a
  particular environmental change or stimulus.
• Control Center- receives and process the
  information supplied by the receptor.
• Effector- a cell or organ that responds to the
  commands of the control center and whose activity
  opposes or enhances the original stimulus.

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Homeostasis in Your House!
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Two Types of Feedback

• 1. Negative Feedback- when the effector(s)
  activated by the control center oppose or
  eliminate stimulus. Most common feedback system
  thermoregulation, salt, energy, pH, etc.

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Another Perspective!
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Negative Feedback-Ignores Minor Changes
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Homeostasis and Negative Feedback

• It is range in which there is a set point.
• The set point is not a fixed value.
• The set point is dynamic and can change for the
  time of day or the individual.

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Blood Sugar Regulation
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Osmoregulation
Water Increase
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The Second Kind of Feedback

• Positive Feedback- initial stimulus produces a
  response that exaggerates or enhances its
  effects. Less common.
• Ex. Labor contractions, Blood clotting

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Positive Feedback
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A Physiological Example
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When positive feedback doesnt stop
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Prolapsed Uterus in a Horse
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Homeostasis is a Balancing Act!

• Organ systems work together to keep within the
  range around the set point.
• The systems are interdependent.
• All are necessary for survival.

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Show Me an Example of Homeostasis!

• The New Living Body-Homeostasis, 1995, VT 574.1
  HOM

Push Here for Another Example