Homeostasis and Feedback Mechanisms

Introduction

  • First lecture conducted online

  • Opportunity to see lecture format

  • Topic focus: Homeostasis

Learning Objectives

  1. Describe the concept of homeostasis

  2. Understand feedback systems and their role in homeostasis

  3. Compare aspects of feedback systems: Negative vs. Positive feedback

Homeostasis Explained

  • Definition: The human body must maintain variables within a narrow range despite environmental challenges.

  • Examples:

    • Cold Environment: In winter in Utah, the body must retain heat

    • Hot Environment: In summer in Utah, the body must cool down

    • Elevation Changes: ascending Mount Timpanogos requires physiological adaptations

Body Temperature Regulation

  • Body reaction to cold: Shivering to generate heat

  • Body reaction to heat: Sweating to cool down via evaporation

  • Regulation involves various physiological components, including:

    • Buffer mechanisms for arterial pH

    • Concentration of ions

    • Blood glucose levels

Blood Glucose Regulation

  • Total blood glucose in a healthy human: 4 grams

    • Consideration of a 40-gram chocolate bar (10x normal): Dangerous spike in blood glucose

  • Consequences: Too much glucose can be lethal

  • Insulin's Role: A hormone that decreases blood glucose by facilitating cellular uptake of glucose

    • Insulin acts when blood glucose spikes outside normal range

    • This mechanism illustrates negative feedback: deviation from normal prompts an action to return to homeostasis

Feedback Mechanisms

Negative Feedback

  • Definition: A response to bring a variable back to normal levels after it has ventured outside the set range

  • Example: Thermostat in an apartment

    • Low temperature activates thermostat

    • Furnace generates heat to restore temperature to set point

  • Biological constant adjustments demonstrating negative feedback principles

Components of a Negative Feedback System

  1. Sensor: Monitors physiological variable (e.g., thermometer in thermostat)

  2. Control Center: Processes information to determine if action is needed (e.g., thermostat)

  3. Effector: Executes change to return variable to normal (e.g., furnace)

Physiology Example of Negative Feedback

  • Body temperature regulation during exercise:

    • Sensor: Thermoregulation center in hypothalamus

    • Control Center: Compares current body temperature to normal levels

    • Effector: Sympathetic nervous system = activates sweat glands

  • Evaporation aids in cooling body down

Complications of Sweating

  • Issues arise in high humidity environments (e.g., Singapore):

    • Sweating becomes less effective due to insufficient evaporation

    • Prolonged exposure can cause heat stroke as body overheats and blood pressure lowers

Positive Feedback Mechanisms

  • Definition: Amplifying a response until a specific event occurs

  • Example: Childbirth

    • Baby's pressure on cervix activates stretch receptors, sending signals to hypothalamus

    • Hypothalamus releases Oxytocin: causes uterine contractions

    • Further contractions increase pressure against cervix, creating a loop until delivery occurs

    • Process characteristics: Temporary and controlled to prevent continuous amplification

Feedback vs. Feedforward Systems

  • Feedback: Reaction to a stimulus

    • Negative Feedback: Restores normalcy after deviation

    • Positive Feedback: Increases response until event completion

  • Feedforward: Anticipatory response to stimuli

    • Example: Salivation response in dogs when they hear a bell (Pavlov's dog experiment)

    • Physiological reactions begin before the actual stimulus (e.g., anxiety increasing heart rate before public speaking)

Conclusion and Final Notes

  • Encourage students to participate in breakout session for review

  • Importance of mastering material for future assessments

  • Emphasis on preparation for upcoming quizzes and midterms.