SACE Biology: Homeostasis Summary

Tolerance Limits

  • Internal variables must remain within tolerance limits for survival and efficiency.

  • Key factors include:

    • Body temperature

    • Water availability

    • Blood glucose levels

    • Carbon dioxide concentration

Law of the Minimum

  • Formulated by Justus von Liebig.

  • States growth is limited by the scarcest resource (limiting factor).

Growth Factors Impacted by Tolerance Limits

  • Water Availability:

    • Critical for maintaining cell integrity.

    • Isotonic balance around 0.9% NaCl.

  • Blood Glucose Levels:

    • Normal range: 75-95 mg/dL.

    • Deviations can lead to hyperglycaemia or hypoglycaemia.

  • CO2 Concentration:

    • Normal range: 5-6% in blood.

    • Excessive CO2 leads to acidosis and toxicity.

Stimulus Response Model

  • Environmental factors (light, sound, touch, etc.) trigger changes.

  • Homeostatic responses counteract these changes.

Sensory Receptors

  • Types of receptors include:

    • Photoreceptors (light)

    • Chemoreceptors (chemicals)

    • Mechanoreceptors (pressure)

    • Thermoreceptors (temperature)

Effectors

  • Effectors (muscles/glands) respond to stimuli:

    • Examples: shivering, sweating, salivating.

Homeostatic Control

  • Involves negative feedback mechanisms.

  • Example: Thermostat analogy for temperature regulation.

Negative Feedback

  • Response diminishes or reverses the original stimulus.

  • Essential for maintaining homeostasis.

Positive Feedback

  • Less common; amplifies the initial stimulus.

  • Example: Breastfeeding triggers hormonal responses leading to milk production.

Nervous and Endocrine Systems

  • Critical for coordinating homeostasis; they influence each other.