Lecture Notes: Homeostasis and Feedback

Introduction

• Homeostasis is essential for life; loss results in disease.
• Defined as the dynamic constancy of the internal environment despite changes in the external environment.

Internal and External Environment

• Internal environment: Inside the body.
• External environment: Outside the body.
• The body maintains a relatively constant internal environment despite external changes.

Dynamic Constancy

• Dynamic implies change; constancy implies stability.
• Variables maintained within limits, not static but not too variable.
• Example: Heart rate fluctuates even at rest; reflects dynamic constancy around a set point value.

Feedback and Homeostasis

• Feedback: System where outputs are used to adjust inputs.
• Feedback loop components:
  • Sensor: Measures outputs and collects data.
  • Integrator: Usually part of the nervous or endocrine system; compares current data to set point.
  • Effectors: Enact changes to bring variables back to set point.

Types of Feedback

Negative Feedback

• Main type used to maintain homeostasis.
• Effectors oppose changes, keeping variables close to set point.
• Example: Thermoregulation
  • Set point 37°C; sensors in skin and hypothalamus monitor temperature.
  • Effectors include vasoconstriction, shivering, metabolic rate adjustment.

Positive Feedback

• Used for extreme responses; destabilizing.
• Effectors enhance changes, pushing variables further from set point.
• Example: Childbirth
  • Stretching cervix increases oxytocin release, increasing uterine contraction.
• Other examples: Blood clotting, immune response.

Summary

• Homeostasis is maintained by negative feedback loops.
• Dynamic constancy involves oscillation around set point.
• Positive feedback loops are used for significant body processes.
• Negative feedback: "The more you have, the less you get."
• Positive feedback: "The more you have, the more you get."