Control System😊

Control System

  • Homeostasis:
    • Maintaining a constant internal body environment.
    • Achieved by control systems.

Prioritization of Parameters

  • Priority of order of correction: pH > BP > Temperature.
  • Types of Control Systems:
    • Feedback control system
    • Feed forward control system

Feedback Control System

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  • Divided into:
    • Positive feedback
    • Negative feedback

Positive Feedback Control System:

  • Also called: Vicious cycle.
  • Process: Substance A stimulates B → B stimulates C → C then stimulates B or A.
  • Outcome: Continuous, escalating cycle
  • Effect: Generally tries to destabilize the system

Beneficial Positive Feedback: CLAPS

  • Blood clotting
  • LH surge
  • Action potential generation:
    • Sodium channel opening → more sodium channel opening (depolarization).
  • Parturition / Lactation:
    • Ferguson reflex/parturition
      • Fetal head → pressure on cervix → oxytocin release → uterine contraction → pushes fetal head further down
    • Lactation → "sucking of baby."
  • Calcium release (ryanodine receptor):
    • Cytoplasmic calcium release → ryanodine receptors → more calcium release.

NOT BENIFICIAL

  • Hemorrhage shock
    • Hemorrhage shock → Irreversible shock → death

Negative Feedback Control System:

  • Process: Substance A stimulates B → B stimulates C → C then inhibits B or A.
  • Negative >> Positive feedback in body
  • Effect: Tries to stabilize the system.
  • Example: 
    • Baroreceptor control system
      • ↓↓ blood pressure if it rises (e.g., due to anxiety).

Feedforward Control System

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  • Aka: Anticipatory control system.
  • Can predict changes ahead of time.
    • Takes precautions to adjust before changes occurs
Examples:
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Thermoregulatory system
Uses both feed forward and feedback systems
Exercise anticipation
• Psychic stimulation
• ↑ in HR and RR before starting exercise
Cephalic phase of gastric secretion
• Food is in the mouth
• Stomach secretes acid
Receptive relaxation of the stomach
• Food is in the mouth
• Stomach relaxes
Cerebellar action in motor coordination
FEEDFORWARD INHIBITION
• One-way control system
• Granular cells -> stimulate basket cells
• Basket cells -> inhibit Purkinje cells
• No feedback from Purkinje cells

Thermoregulatory system:

  • Note: Thermoregulation uses both feed forward and feedback systems.
    • Feedforward system:
      • Predictive control.
      • Based on skin temperature changes.
      • Hypothalamus raises core body temperature before it actually falls.
      • Activates heat conservation/generation mechanisms early by hypothalamus
      • Example: shivering, vasoconstriction.
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    • Feedback system:
      • Responds to actual changes like ↑↑ metabolic rate, behavioral changes like seeking warmth

Cerebellar inhibitions

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Gain of the Control System

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  • Gain = How much corrected
    Residual Error
  • Example Calculation:
    • Anxiety causes BP rise (disturbance): 10 mm Hg.
    • Baroreceptor corrects (correction): 8 mm Hg decrease.
    • Residual error: 10 mm Hg - 8 mm Hg = 2 mm Hg.
    • Gain = 8 / 2 = 4.
  • Normal baroreceptor gain: - 2.
    • Correction is opposite to disturbance
  • Thermoregulatory gain: - 33
    • Very powerful
      • Sensation
      TRP Channels
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      For Heat
      • TRP V1 (Vanilloid)
      V1 A1 M2 M3
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      • TRP M2
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      • TRP M3
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      For Cold
      • TRP M8 (Menthol)
      8 → snowman → cold
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      • TRP A1
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  • Renal control of blood pressure and blood volume
    • Infinite gain:
      • 100% correction of BP/volume to normal
      • Gain = Correction / 0 = Infinity.
      • NO RESIDUAL ERROR
      • Slow system, takes time
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