Homeostasis and Feedback Mechanisms Vocabulary

Introduction to Homeostasis and Feedback Mechanisms

  • Definition of Homeostasis: Homeostasis is described as a "balancing act" within the body to maintain a stable internal environment.

  • Types of Feedback Systems: There are two primary mechanisms or systems by which homeostasis is maintained:

    • Negative Feedback: The most common form of homeostatic mechanism in the human body.

    • Positive Feedback: Rare at the organ system level, though it does occur at the cellular level.

The Negative Feedback Mechanism: Household Analogy

  • The Household Model: A common way to understand negative feedback is through the heating and cooling system used to control the temperature in a home or apartment.

  • The Control Center: An essential component of every negative feedback system. In a home, the thermostat serves as the control center.

  • The Set Point: This is the specific value at which the system is intended to stay (e.g., the specific temperature you pick for the room).

  • The Receptor (Sensor): In order for the system to function, there must be a component that measures the current state of the variable. In a household, this is a thermometer.

  • The Process of Regulation:

    • Stimulus: In the summertime, the room temperature increases.

    • Information Relay: The thermometer measures this increase and relays the data to the control center (thermostat).

    • Comparison: The control center compares the measured temperature against the established set point.

    • Effector Action: If the temperature rises above the set point, the control center sends a signal to an effector—in this case, an air conditioner.

    • Response: The air conditioner blows cool air into the room, and the temperature returns to its set point.

    • Prevention of Over-cooling: The thermometer continues to measure the temperature. If the temperature falls below the set point, the control center sends a signal to turn the air conditioner off.

  • The Oscillating Graph: Because the system is constantly adjusting, the actual temperature does not stay perfectly flat at the set point. Instead, it creates an oscillating graph that moves slightly above and below the set point depending on the sensitivity of the system.

  • Additional Analogy: The same principle of negative feedback applies to the cruise control system in an automobile.

Human Body Temperature Regulation

  • The Physiological Application: The human body uses negative feedback to regulate internal body temperature.

  • The Stimulus: External environmental factors, such as summer heat or physical exertion (working outside), cause the body to build up heat.

  • The Control Center: The control center for human body temperature is located in the hypothalamus of the brain.

  • Human Set Points: The hypothalamus maintains a set point of approximately 98.6∘F98.6^{\circ}\text{F} or 37∘C37^{\circ}\text{C}.

  • Disturbance of Homeostasis: When body temperature increases beyond the set point, homeostasis is disturbed.

  • The Role of Receptors: Receptors located throughout the body monitor and measure temperature, relaying this information to the hypothalamus.

  • The Body's Response (Cooling):

    • If the measured temperature exceeds 37∘C37^{\circ}\text{C}, the hypothalamus sends signals to structures called effectors.

    • Arteriole Response: Smooth muscle in the arterioles dilates (vasodilation), bringing warm blood to the surface of the skin.

    • Glandular Response: Sweat glands are activated to increase sweat production.

    • Evaporation: The evaporation of sweat from the skin surface cools the blood, allowing body temperature to return to the set point.

  • The Body's Response (Conserving Heat):

    • If the body temperature gets too low, sweating stops.

    • Blood vessels (arterioles) constrict to keep warm blood concentrated toward the center of the body.

  • Resulting Oscillation: Human body temperature follows an oscillating graph around the normal range of 37∘C37^{\circ}\text{C}.

Specific Components of a Feedback System

  • The Stimulus: Defined as a change in a variable within the body.

  • The Receptor (Sensor): The component that monitors the variable and detects changes.

  • The Control Center: The location where the set point is stored and where the determination is made whether a variable has risen above or fallen below that set point.

  • The Effector: Structures in the body that act and respond to signals from the control center to maintain the normal set point.

  • The Four Physiological Effectors: In physiology, there are specifically four types of effectors (composed of specific cells) that respond to the control center:

    1. Skeletal muscle.

    2. Cardiac muscle.

    3. Smooth muscle.

    4. Glands.