L1.8: Homeostasis

• • Self-regulating process
  • Maintenance of relatively stable internal conditions
  • Dynamic state of equilibrium: internal conditions change and vary but always within relatively narrow limits.
  • Maintains internal stability while adjusting to external conditions
  • Necessary for normal body functioning and to sustain life.
  • “Homeo” = similar, “Stasis” = standing still


  Homeostasis
• Main controlling systems of homeostasis

  • nervous system
  • endocrine system

  Homeostatic imbalance

  • a disturbance in homeostasis results in disease.
• Control mechanisms

  • receptor
  • control center
  • effector
• • Type of sensor that monitors and responds to changes in the environment called stimuli, by sending information (input) to the second component, the control center.
  • uses the afferent pathway


  receptor
• • Determines the level (set point) at which a variable is to be maintained.
  • This component analyzes the information it receives
  • Then, it determines the appropriate response or course of action.
  • integration center


  control center
• • Provides the means for the control center’s response (output) to the stimulus.
  • Information flows from the control center to the effector along the efferent pathway.
  • The results of the response and then feedback to influence the stimulus (the original change).


  effector
• Homeostasis is so important that most diseases can be

  regarded as being the result of its disturbance, a condition

  called homeostatic imbalance. As we age, our body organs

  become less efficient, and our internal conditions become less

  and less stable. These events place us at an increasing risk

  for illness and produce the changes we associate with aging.

  homeostatic imbalance
• Feedback mechanism

  • negative feedback
  • positive feedback
• • Includes most homeostatic control mechanisms.
  • The net effect of the response to the stimulus is to either shut off the original stimulus or reduce its intensity.
  • Works like a household thermostat

  negative feedback
• • Rare in the human body
  • Increases the original stimulus (disturbance) to push the variable farther.from its original value.
  • Reaction occurs at a faster rate
  • In the body, positive feedback occurs in blood clotting and during the birth of a baby.


  Positive feedback