Overview
This lecture explains the key elements of feedback loops, including their structure and biological examples, to help you understand how systems maintain stable conditions.
Components of a Feedback Loop
- A feedback loop exists when system output is fed back as input, forming a loop.
- Key elements: receptor (detects change), effector (acts to correct change), stimulus (change detected), and response (action taken).
- Receptors and effectors are organs; stimulus and response are actions.
Structure and Pattern of Feedback Loops
- Feedback loops are often illustrated as figure-eights, with receptors in the center and effectors at the top and bottom.
- Negative feedback loops keep variables near a set point, correcting deviations.
- Positive feedback loops amplify changes, moving the system away from a set point.
Feedback Loop Analogy Examples
- Speed sign example:
- Eye is the receptor (detects speed); foot is the effector (presses brake or gas).
- Going too fast (stimulus): slow down (response); going too slow: speed up.
- Thermostat example:
- Thermostat is the receptor (senses temperature); furnace is the effector.
- Room too hot: furnace turns off; room too cold: furnace turns on.
Biological Feedback Loops
- Thermoregulation:
- Receptor: hypothalamus in the brain detects body temperature.
- Effectors when too hot: sweat glands (sweat), capillaries (dilate).
- Effectors when too cold: capillaries (constrict), muscles (shiver), goosebumps.
- Blood glucose regulation:
- Receptor: pancreas monitors blood glucose.
- If too high: beta cells release insulin (enables cells to absorb glucose).
- If too low: alpha cells release glucagon (liver releases glucose into blood).
Key Terms & Definitions
- Feedback Loop — System where output is recycled as input to maintain stability.
- Receptor — Organ that detects changes in a condition (stimulus).
- Effector — Organ that acts to correct the change (response).
- Stimulus — Change detected by the receptor.
- Response — Action carried out by the effector to restore balance.
- Negative Feedback — Counteracts change to maintain a set point.
- Positive Feedback — Amplifies change away from a set point.
Action Items / Next Steps
- Be able to identify receptors, effectors, stimuli, and responses in feedback loops.
- Practice drawing and labeling feedback loop diagrams for biological processes.
- Review textbook examples of feedback loops (e.g., thermoregulation, blood glucose).