Negative Feedback: The Simplest Regulation
When something in the body is not at ideal conditions, a signalling response is triggered by a group of cells. This signalling response then triggers “worker cells” that will fix the problem. The beautiful part of this cycle is that the signal will stay active until those “worker cells” solve the problem. Once the signalling cells detect that the conditions have been restored, the signal stops and, as a result, the “worker cells” do not get the stimulus to continue working.
That may sound more confusing than it really is so let’s work through a well known example: the insulin response. Here is how homeostasis works in a normal person’s digestive system:
Diabetes and the Regulation of Insulin
The function of insulin is to signal to the cells of the body to take in sugar from the bloodstream. These sugar levels are detected by certain cells in the pancreas (beta cells). These beta cells are also responsible for releasing insulin.
Normal Function of Insulin
After a meal, the intestines absorb sugar and push it into the bloodstream. As a result, the cells in the pancreas detect high sugar levels in the blood. They respond by secreting insulin, sending a signal to the body to absorb more glucose. As the cells take in the sugars, the blood levels of sugar lower until the initial levels are reached. At this point, the cells in the pancreas realize that blood sugar is normal again and stop secreting insulin. Once they stop secreting insulin, the body cells do not receive the signal to take in sugar so they stop. The cycle restarts when the person eats again.
Now, let us focus on what happens when these mechanisms fail in the cases of type 2 and type 1 diabetes.
Type 2 Diabetes
Type 2 diabetes occurs in people that often have a lot of sugar in their blood. In an attempt to keep these levels down, the beta cells constantly release massive amounts of insulin to signal cells to take in the sugar. Unfortunately, the cells of the body begin to gain a tolerance to insulin since it is always around (just like alcohol tolerance). This means even more insulin needs to be released for the same effect. Thus, the cells gain even more resistance to it.
Think of it as ignoring the most important alarm of your life except the alarm gets louder every the longer you ignore it. At the worst case scenario, the incredibly loud alarm would have made you go deaf and so you will sleep soundly forever.
Ultimately, the beta cells have a maximum amount of insulin they can secrete so the blood sugar levels remain high all the time, and spike even higher every time the person eats something. Eventually, the body cells grow so resistant to insulin that they can’t absorb sugar at all. This causes the cells to die off, literally starving while surrounded by food. This is why diabetics lose limbs: the nerves and muscles slowly starve to death and the person does not feel their body decay. As you can see, interfering with how homeostasis works in nature leads to dire consequences for the individual. This modern disease is one of the most prevalent conditions in the world.
Type 1 Diabetes
In the case of type 1 diabetes, the immune system accidentally identifies the beta cells of the pancreas as foreign. As a result, the white blood cells destroy the cells, leaving the body with no way to release insulin or monitor blood sugar. This is why type 1 diabetics have to ingest insulin with a meal or have an insulin pump monitoring their blood sugar for them, acting as artificial beta cells.
This is just one simplified example of negative feedback. In reality, there is a parallel system in charge of making sure the blood sugar does not fall below desired amounts, a key system involved in weight loss (glucagon). However, it serves the purpose of explaining how homeostasis works in organisms.
What about crisis situations? For example, what if you cut yourself and are bleeding heavily? It is important that the bleeding stops as fast as possible. Organisms have developed another system of regulation for time sensitive situations. This system is called positive feedback.