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HOMEOSTASIS. DR ROBERT RYAN BUENAVENTURA MEDICAL GROUP APRIL 24, 2006. Homeostasis. From the Greek roots Homo: alike or the same Stasis: to stand or posture Term coined by Walter Cannon in 1932. Homeostasis.

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homeostasis

HOMEOSTASIS

DR ROBERT RYAN

BUENAVENTURA MEDICAL GROUP

APRIL 24, 2006

homeostasis1
Homeostasis
  • From the Greek roots
    • Homo: alike or the same
    • Stasis: to stand or posture
  • Term coined by Walter Cannon in 1932
homeostasis2
Homeostasis
  • Ability or tendency of an organism/cell to maintain internal equilibrium by adjusting its physiological processes
    • e.g., temp, pH, blood pressure, PCO2, etc.
  • Negative or Positive Feedback
feedback
Feedback
  • Negative Feedback
    • Slows down process to return to equilibrium
  • Positive Feedback
    • Accelerates process away from equilibrium
feedback cont d
Feedback (cont’d)
  • Stock Market
  • Aircraft autopilot
  • Computer modeling
  • Biological systems
  • Genes
feedback cont d1
Feedback (cont’d)
  • Control triangle preprogrammed with desired ranges
  • Input arrives and acted upon in control triangle to provide an output
  • Output sampled and fed back to control triangle
  • Output modified to make sure output stays within programmed range for center
types of feedback
Types of Feedback
  • Negative Feedback: change in an environment causes response that returns conditions to original state
    • Thermostat
  • Positive Feedback: response of the system is to change that variable even more in the same direction
    • “Sim City”
    • Two in human body
nervous system
Nervous System
  • Body’s surveillance system
    • Blood pressure, temperature, pH, etc.
  • Sensory centers
    • Brain or spinal cord
    • Barrage of input integrated and response generated
  • Organs convert signal into some form of action
    • E.g., movement, changes in heart rate, release of hormones, etc.
  • Reflex arc
cardio respiratory system
Cardio-Respiratory System
  • Maintain homeostasis and deliver oxygenated blood to cells
  • Negative Feedback
    • Blood Pressure
    • pH
    • PCO2
  • Hyperventilation example
endocrine system
Endocrine System
  • Elegant feedback networks
  • Affects activities of cells, tissues, and organs throughout the body
  • Controls slower, longer lasting responses to internal stimuli
  • Self-Regulating Negative Feedback Mechanism
    • Hypothalamus
    • Anterior Pituitary
    • Other Endocrine End Organs
endocrine system cont d3
Endocrine System (cont’d)
  • Positive Feedback Loop
    • Childbirth
      • Increased rate of contractions causes increased rate of stretch receptor stimulus (feedback)
      • Continues positive feedback loop until baby is delivered
endocrine system cont d4
Endocrine System (cont’d)
  • Positive Feedback Loop
    • Name the other positive system found in mammals
endocrine system cont d5
Endocrine System (cont’d)
  • Blood clotting
    • Self-catalytic, self-accelerating effect
    • Clotting process begins
      • Runs faster and faster
      • Until bleeding stops
    • Positive feedback loop is part of a larger negative feedback loop
      • Activated by bleeding
      • Ultimately works to stop the bleeding
summary
Summary
  • Homeostasis is achieved by
    • Mainly negative feedback
    • Infrequent cases positive feedback
  • Negative feedback’s goal is to maintain equilibrium
  • Positive feedback’s goal is to accelerate away from equilibrium
  • Endocrine, Nervous and Cardio-Respiratory systems all use feedback to maintain life
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