Feedback Loops - Online Tutor, Practice Problems & Exam Prep

Feedback loops are essential for maintaining homeostasis in the body. Negative feedback mechanisms counteract changes by moving the system towards a set point, promoting stability. For example, if body temperature rises, mechanisms activate to cool it down. In contrast, positive feedback amplifies changes, moving the system away from the set point, like in childbirth where contractions intensify. Understanding these loops is crucial for grasping physiological processes, as they illustrate how the body self-regulates and responds to stimuli, ensuring balance and function.

Introduction to Feedback Loops

Now we're going to talk about feedback loops in the body. We're going to do this because homeostasis is largely controlled through feedback loops. A feedback loop is going to occur when a change to the internal environment causes a response, and that response is the feedback part. And the response is going to alter the internal environment. So if you remember where we started, we started with a change to the internal environment.

We're back at the beginning. That's the loop. There are going to be 2 types of feedback loops that we're going to talk about. The first is negative. Negative feedback loops move the system in the opposite direction to the original stimulus.

In contrast, positive feedback loops move the system in the same direction as the original stimulus. Alright. We're going to look at both of these in a little bit more detail here. Let's start with negative feedback. Negative feedback moves the system towards the set point and that maintains homeostasis.

That's why we're talking about this one first and we're going to go into it in a lot more detail in upcoming videos. We are concerned with maintaining homeostasis because that's going to be one of the major things that happens in physiology in the body. So if we see our set point here on this little dial, we have a little dial and an arrow pointing up, and it looks like it has fallen off to the right here. Well, negative feedback is going to move the system towards the set point in the opposite direction of the stimulus, so it is going to push this dial back up to where it started. I like to think of this as a person balancing on one leg, and so we have a little image of someone balancing on one leg here to remind you of that.

Homeostasis, we said, is standing still in one place, but it is a dynamic process. If you're standing on one leg, you might look kind of stable, but there is all sorts of negative feedback going on. If you lean forward, your body pushes a little bit back. As you lean one way, you stick your arms out to fix your balance and you come back to the center. All of your movements are going to be opposite the stimulus, so that you return to your set point.

This means that negative feedback is kind of self-regulating. It turns itself off. It gets back to the set point and it's all set. It also means it's going to be more common in the body. Again, we're trying to maintain homeostasis.

We're trying to stay at set points. Negative feedback is really good at that. In contrast, we have positive feedback. Positive feedback moves the system away from the set point. So we have our little dial here, and we have our set point up the middle.

And you can imagine if the set point falls off to one side, what positive feedback is going to do is just going to keep pushing it farther and farther in the same direction. I like to think of this with the analogy of a fire. When you start a fire, you light some paper, it generates heat. The more heat it generates, the more things catch on fire. The more things that catch on fire, the more heat it generates, and the fire just gets bigger and bigger, just like positive feedback.

Now importantly, this requires sort of an off switch in the body. You don't want these positive feedback systems getting out of control and they have the potential to. It also means they're going to be a little bit less common, well, rather a lot less common because moving away from the set point, well, that's not what we want to do if we're maintaining homeostasis. The last thing that I want to note here is that a misconception some people have when we say negative, we often think on, like, a number line.

It means going less than. Negative feedback could push something in a positive or negative direction. It just depends on what the original stimulus was. Negative, in this case, means opposite. Same thing for positive.

Normally, you think on a number line, positive means more. Well, positive feedback just means in the same direction. It could be that something's getting less, and then positive feedback just makes it get less and less and less continually. Alright. With that in mind, as I said, we're going to look at negative feedback in a lot of detail, and we'll look at positive feedback in some detail as well coming up.

And I'll see you there.

Feedback Loops Example 1

This example gives us two feedback loops and asks us to identify them as either positive or negative feedback. So let's take a look. First up, we have oxytocin, a hormone that stimulates labor contractions. Labor contractions force the head of the baby downward, resulting in pressure on the cervix. Pressure on the cervix is a signal to the pituitary gland to release more oxytocin.

Alright. Give yourself a second. Does that sound more like positive feedback or negative feedback? Well, our original stimulus is oxytocin. That causes labor contractions, which is pressure on the cervix, which is a signal to release more oxytocin.

This oxytocin is going to increase labor contractions, increase pressure on the cervix, which is going to increase oxytocin release. Right? So we're getting more and more. We are moving further away from the starting point. So that, to me, sounds like positive feedback.

Next, we have the process when body temperature rises, causing the skin to produce sweat. The evaporation of sweat will cool the body. If body temperature falls, the body will shiver. The action of shivering generates heat to warm the body. Now, think about that one for a second.

Okay. Sweat cools the body when you're too hot. So the temperature goes up, sweat cools the body, it pushes back against the original stimulus. Shivering warms the body when the temperature falls. Shivering is going to push back against the original stimulus.

When you're pushing back against the stimulus towards the starting point, that is going to be negative feedback. We are going to go into more detail on both of these specific feedback loops in future videos. I'll see you there.

Which type of feedback begins as a response to a change in the internal environment?

• A. Positive feedback mechanisms.
• B. Negative feedback mechanisms.
• C. Both positive and negative feedback begin this way.
• D. Neither positive nor negative feedback begin this way.

Which statement about positive and negative feedback loops is correct?

• A. Negative feedback always lowers the value of the original stimulus, while positive feedback always increases it.
• B. Positive feedback loops tend return a system to a set-point, negative tend to move the system away. 
• C. Negative feedback loops tend return a system to a set-point, positive tend to move the system away. 
• D. Negative feedback always increases the value of the original stimulus, while positive feedback always lowers it.

Glucagon is a hormone that is released by the pancreas in response to falling blood glucose levels. The release of glucagon is part of a negative feedback mechanism. Based on that information, what effect would you expect glucagon to have on the body?

• A. Glucagon signals the liver to break down glycogen and release the resulting glucose into the bloodstream.
• B. Glucagon signals the liver to stop all glycogen breakdown and synthesis to try to maintain glucose levels. 
• C. Glucagon signals the liver to remove glucose from the bloodstream and store it as glycogen.
• D. Glucagon signals the small intestine to reduce absorption of glucose into the blood.

Here’s what students ask on this topic:

What is a feedback loop in the context of homeostasis?

A feedback loop in the context of homeostasis is a biological mechanism where a change in the internal environment triggers a response that influences that change. This loop helps maintain stability within the body. There are two main types of feedback loops: negative and positive. Negative feedback loops counteract changes by moving the system towards a set point, promoting stability. For example, if body temperature rises, mechanisms activate to cool it down. Positive feedback loops, on the other hand, amplify changes, moving the system away from the set point. An example is the intensification of contractions during childbirth. Understanding these loops is crucial for grasping physiological processes and how the body self-regulates to ensure balance and function.

How does a negative feedback loop work in the body?

A negative feedback loop works by detecting a change in the internal environment and initiating a response that counteracts that change, moving the system back towards a set point. For instance, if the body temperature rises above the set point, sensors in the skin and brain detect this change. The hypothalamus then triggers mechanisms such as sweating and vasodilation to cool the body down. Once the temperature returns to the set point, these mechanisms are turned off. This self-regulating process is crucial for maintaining homeostasis, as it ensures that physiological parameters remain within a narrow, stable range.

Can you provide an example of a positive feedback loop in the human body?

An example of a positive feedback loop in the human body is the process of childbirth. During labor, the release of oxytocin causes uterine contractions. These contractions push the baby towards the cervix, which stretches and sends signals to the brain to release more oxytocin. This increase in oxytocin intensifies the contractions, pushing the baby further down the birth canal. This loop continues until childbirth is complete. Positive feedback loops amplify the initial stimulus, moving the system away from the set point, and typically require an external 'off switch' to stop the process.

Why are negative feedback loops more common in the body than positive feedback loops?

Negative feedback loops are more common in the body because they promote stability and help maintain homeostasis. These loops counteract changes by moving the system back towards a set point, ensuring that physiological parameters remain within a narrow, stable range. This is essential for the proper functioning of the body. In contrast, positive feedback loops amplify changes and move the system away from the set point, which can lead to instability if not properly regulated. Therefore, while positive feedback loops are important for certain processes like childbirth, they are less common because they do not contribute to maintaining homeostasis.

What is the role of the hypothalamus in feedback loops?

The hypothalamus plays a crucial role in feedback loops, particularly in regulating homeostasis. It acts as a control center that receives input from various sensors in the body and initiates appropriate responses. For example, in a negative feedback loop regulating body temperature, the hypothalamus detects changes in temperature through sensors in the skin and brain. If the temperature rises, the hypothalamus triggers mechanisms such as sweating and vasodilation to cool the body down. Conversely, if the temperature drops, it initiates shivering and vasoconstriction to generate and retain heat. By coordinating these responses, the hypothalamus helps maintain a stable internal environment.