Homeostasis

Maintaining stable internal conditions via feedback loops

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Chapter Summary

Homeostasis is the dynamic equilibrium organisms maintain. Feedback loops—negative and positive—detect deviations and trigger physiological responses to restore or amplify change.

What Is Homeostasis?

Homeostasis refers to the processes that keep internal variables (temperature, pH, glucose levels, fluid balance) within a narrow, healthy range despite external fluctuations.

  • Receptor: senses change
  • Control Center: processes signal (e.g., hypothalamus)
  • Effector: carries out response (e.g., sweat glands, muscles)

Blood Glucose Regulation

Blood sugar regulation diagram

Insulin (lowers sugar) and glucagon (raises sugar) form a classic negative‐feedback loop to maintain ~90 mg/dL blood glucose.

Negative Feedback

Negative feedback reverses a deviation from a set point:

  • Thermoregulation: >37 °C → sweat; <37 °C → shiver
  • Glucose Control: ↑ blood sugar → insulin; ↓ sugar → glucagon

Thermoregulation Simulator

Body Temperature: 37°C

Positive Feedback

Positive feedback amplifies a change rather than reversing it:

  • Childbirth: uterine contractions → oxytocin → stronger contractions
  • Blood Clotting: platelet activation → more platelet recruitment

Contraction Simulator

Contraction Intensity: 1

Key Terms

Quiz Yourself

1. Which is positive feedback?

2. Which hormone raises blood sugar?