The Positive Feedback Loop: An Emergency Response
Positive feedback is the second system that explains how homeostasis works. The loop is designed to exponentially speed up a process and address an issue. The way this system works is quite interesting; an initial stimulus triggers a reaction that produces a chemical. The chemical that is produced amplifies the signal that is causing it to be made. This process continues until the chemicals can no longer be produced and the original chemicals are naturally broken down by enzymes, or until another signal stops the process.
Clotting
Back to the example… when a blood vessel is cut open, the vessel wall releases warning chemicals. These chemicals signal platelets to stick to the damaged walls. As these platelets stick to the cut, they release more of the same chemicals, increasing how many platelets stick to the vessel. Eventually, the clot will cover up the injured site, initiating a negative feedback response to stop the platelets from clotting endlessly.
As you can imagine, this process is unique to only a few processes because they tend to escalate quickly. The only other well known example of positive feedback in humans is that of childbirth contractions in women.
Conclusion
These examples barely scrape the surface of how homeostasis works. There are countless examples of this kind of regulation all across nature, from the regulation of water uptake in plants to nucleotide concentrations in bacteria. All of this regulation is essential to the survival of life, especially when looking at organisms as an infinitely complex set of chemical reactions.
I challenge you to look around in your daily life and find examples of such phenomena. It is surprising how common these mechanisms are in all complex communities of living beings, from cells to civilizations.
For example, next time you hear a baby crying, instead of ignoring it, think about why it is crying and what will make it stop. When talking with another person, note their facial expressions and how you respond to their subtle emotional signals. Thinking like this will allow you to bring this topic to life. It will put homeostasis in context of your world and, ultimately, the universe itself.