Feedback Loops: Negative Feedback - Online Tutor, Practice Problems & Exam Prep

Negative feedback loops are essential for maintaining homeostasis by returning physiological variables to their set points. Key components include receptors that detect changes, control centers that process information, and effectors that enact responses. For example, in thermoregulation, temperature-sensitive cells in the hypothalamus act as both receptors and control centers, signaling sweat glands to cool the body or skeletal muscles to generate heat when cold. This dynamic process involves vasodilation and vasoconstriction to regulate blood flow, ensuring optimal body temperature is maintained.

Negative Feedback Loops

Now, we're going to take a look at negative feedback loops in a little bit more detail. So remember that negative feedback loops return the body to a set point, and by doing this they oppose the direction of the stimulus. So if you have some variable in the body and it moves off its set point, a negative feedback loop is going to push back and push it back to where it started. Now, the nervous and endocrine systems control many feedback loops in the body both positive and negative, but we're focusing on the negative now. Now that's going to be important going forward, so keep that in mind.

So let's now break down these different components. There are going to be 3 main components to a negative feedback loop. First up, we have the receptor. The receptor is going to measure the stimulus. And by stimulus, we just mean whatever variable we're talking about; it's going to change, and that's going to be the change in the internal environment that will be measured by the receptor.

The receptor will then send a signal to the control center or integration center. The control center, sometimes called the integration center, is going to process that information and signal some sort of response. Now, it's the nervous and endocrine systems that so often play the role of the control center. Now, of course, the control center doesn't do the response itself; it sends a signal to the effector, and the effector carries out the action to restore the set point. Okay.

So we have an example here to see this in action, and we have a diagram of a man and it's zoomed in on his parathyroid glands here, these four little glands in the neck, and it shows an arrow going down to his bones here. It should go down to his collarbone. Let's see what's going on. So first off, it says parathyroid gland detects low blood calcium. Well, it sounds like the parathyroid gland in this case is acting as the receptor.

It's measuring a physiological variable, in this case, the calcium level in the blood, and it recognizes the blood calcium is too low. So it's going to send a signal. It's going to here it says the parathyroid gland then integrates low blood calcium signal and releases parathyroid hormone. So in this case, both the parathyroid gland is acting as both the receptor and it's acting as the control center. The control center, again sometimes called the integration center, is going to process that signal from the receptor, figure out what needs to happen, and send a signal out so the body can respond.

That signal is going to go to well, let's see what happens. The bone tissue is stimulated by the parathyroid hormone to increase blood calcium. So in this case, and this is why we have this arrow coming down from the parathyroid gland to the bone, the bone tissue is acting as the effector. The hormone from the parathyroid gland is recognized by the bone tissue. The bone tissue takes some calcium for the bone, puts it back in the blood, and that's going to push that blood calcium levels back up.

Okay. So that is the overall general idea of how a negative feedback loop works. You do not need to know these details, but you should be able to see a negative feedback loop and break it down into its different components, like we just did here. We're going to practice that some more going forward, and I'll see you there.

Feedback Loops: Negative Feedback Example 1

This example asks us to identify the components of a negative feedback loop. Alright. So you stand up quickly, causing your blood pressure to fall, and you feel light-headed. Your pulse begins to increase, raising your blood pressure. After a moment, you feel fine.

Using a diagram below, first identify the stimulus and the response, then label the receptor, control center, and effector. Okay. So it shows this picture of a woman here. We can see her blood vessels, her heart, and her brain, and it looks like there is a loop going. It starts at the heart, and an arrow goes up to the brain stem and then back down to the heart.

So first off, it says to identify the stimulus and the response. So take a second thinking about what it said in that paragraph above. What do you think the stimulus is? Well, what started this whole thing off? It started off because the blood pressure fell.

Right? That stimulus is a thing that moves out of the range of the normal physiological range, one under homeostasis. So my stimulus is going to be blood pressure falls. Alright. Now think what is the response?

Well, in a negative feedback loop, the response is going to push in the other direction, and sure enough, we're going to raise the blood pressure. So that response is going to be blood pressure rises. Okay. Let's look at the different components of the feedback loop over here. Remember, we have a receptor, a control center, sometimes called the integration center, and an effector.

So let's read each one and think how they match up. First up, we have the medulla processes low blood pressure signal and sends a message to the heart. Think what that sounds like. Well to me, it's processing low blood pressure and sending a message to the heart. That sounds like a control center.

We said the control center is often part of the nervous or endocrine systems, and it's going to integrate that response and tell the body what to do and how to respond. So the control center, I'm actually just going to draw a line to the medulla and the brain stem right there. The next one we have, it says after standing up quickly, baroreceptors above the heart, measure a drop in blood pressure. Alright. What do you think that sounds like?

Well, right there in the name baroreceptors. They are measuring a drop in blood pressure when it measures something. That is a receptor. And I'm just going to go ahead and draw a line to the heart. And then finally, we have the heart rate increases to increase blood pressure.

What does that sound like? That's going to be the effector. The effector is the thing that goes ahead and pushes back and changes the physiological condition to push it back to the original condition. So again, I'll draw an arrow back up to the heart for that one. Okay.

With that, we have some more practice problems below. I'll see you in the next video.

What is the role of the effector in a negative feedback loop?

• A. The effector works to restore conditions in the original tissue.
• B. The effector is another name for the stimulus in a feedback loop. 
• C. The effector measures changes in a tissue to initiate a response.
• D. The effector integrates stimuli and sends messages for how the body should respond.

An increase in blood solute concentration, as measured by the osmoreceptors of the hypothalamus, indicates a net loss of water in the body. The hypothalamus responds by both stimulating a thirst response and releasing antidiuretic hormone. Antidiuretic hormone directs the kidneys to recover more water during urine production. In this case, what two parts of a feedback loop are occurring in the hypothalamus?

• A. The control center and the response.
• B. The receptor and the control center.
• C. The control center and the effector.
• D. The receptor and the effector.

Negative Feedback Loops: Temperature

We've been talking about negative feedback loops, and up until now, I said don't worry about the specifics for any one negative feedback loop. Here, we're going to worry about the specifics for one negative feedback loop. We're going to talk about temperature. Now don't worry too much. You probably know a lot of the details about thermal regulation already.

We just need to map them onto the context that we've been talking about. So thermoregulation follows a negative feedback mechanism, and we can break it down into components like we've been practicing. We have first the receptors. The receptors, in this case, are going to be the temperature-sensitive cells of the hypothalamus. The hypothalamus is a region in your brain.

As blood goes up into your head, the hypothalamus or the temperature-sensitive cells in your hypothalamus measure the temperature of that blood. And if it's outside that narrow range that's acceptable, it's going to send a signal to the control center. Remember, sometimes that's called the integration center. In this case, the control center is the thermal regulatory center in the hypothalamus. So the hypothalamus both has the receptors and the control center in this case.

The control center is then going to integrate that information and send out the appropriate response to the effectors. For thermal regulation, the first type of effector is going to be the sweat glands. The sweat glands of the skin are going to respond when the body is too hot. And to remind you of that, we have this picture of this man in the sun, and he is dripping sweat because it's hot outside. Our next effector is going to be the skeletal muscles, and they respond by shivering when the body is too cold.

And to remind you of that, we have this picture of a woman and she is shivering all bundled up with snow around her because she's, well, obviously quite chilly. And then finally, we have smooth muscles controlling blood flow. They respond to both hot and cold, but they're going to respond differently depending on what the temperature is. So to look at this in a little bit more detail, we have this little diagram here, and on the left, we have too cold, and on the right, we have too hot. So we have our little meter here, and you can imagine that if the temperature meter goes too cold, well, the receptors and the thermoreceptors in the brain are going to recognize that.

They're going to send a message to the control center, the hypothalamus. The control center is going to integrate that information and send a message to the effectors, and the effectors are going to respond, the skeletal muscles and the smooth muscles. The skeletal muscles are going to start shivering. And when you shiver, the movement of muscles generates heat. So that shivering, those muscle contractions are going to increase your body temperature.

The blood flow to the skin is going to decrease, and we're going to call this vasoconstriction. So 'vaso' refers to a blood vessel and 'to constrict' means to get smaller or tighter. So the blood vessels to the skin are going to get smaller. That means less blood is going to the skin. That means more blood is at the body core.

Close to the skin is going to be cold because it's cold outside, so you want to keep that blood on the inside of your body, deep inside your body. That also is going to raise your body temperature. So those two things together are going to push back against the stimulus and return your body temperature to normal. Now when your body gets too hot, the same thing happens. You can imagine our meter here.

It's going off into the red. Well, the receptors in the brain, the thermoreceptors in the brain are going to recognize that. They're going to send a message to the control center in the hypothalamus. The hypothalamus is going to respond by sending a message to the effectors, in this case, the sweat glands and the smooth muscles. So sweating. You cover your body with a layer of water and that water evaporates. That's evaporative cooling, and that will cool the body. That will cause your temperature to go down. Blood flow to the skin is going to increase. We're going to call this vasodilation.

The blood vessels to the skin, 'vaso' blood vessels, are going to dilate. They're going to get bigger around, meaning more blood is going to go to the skin. As the blood is close to the skin, it's going to get cooled by that evaporative cooling from the sweat and your temperature, again, is going to go down. That's why if you exercise on a hot day, you get really flushed. It's trying to cool down the body, more blood vest more blood in the blood vessels close to the skin.

All of that together is going to push back against the original stimulus, and it's going to cool the body. Okay. With that, we have some practice problems below, and I'll see you in the next video.

Feedback Loops: Negative Feedback Example 2

This example tells us that after exercising outdoors on a summer day, you find that your face is flushed and red, your clothes are drenched in sweat. What variable is your body controlling for? What is the stimulus that initiates the negative feedback loop? And in your own words, how do both a red face and sweaty clothes relate to the negative feedback loop in this example? All right.

So let's take these one by one. What is the variable that your body is controlling for? Take a second. You know what it is. Sounds to me like the variable is temperature.

The responses there are classic responses to a change in body temperature. All right. And specifically, what is the stimulus? How is the temperature changing? Well, the stimulus to me sounds like the body is too hot.

The body is too warm. So an increase in body temperature is going to cause these responses. And now let's think specifically how do both these responses relate to the body getting too warm and the negative feedback loop. So we'll start with the red face. All right.

Why do you get a red face when you get too hot? Well, a red face, you're shunting blood to the skin, and we call that vasodilation of the blood vessels to the skin. And that specific word vasodilation, you might need to know it. Check your notes to be sure. So more blood to the skin means that that blood can take the warm body heat and radiate it out, and that will help cool off your body.

Okay. So why do you get sweaty clothes? Well, sweat equals evaporative cooling. When the water in the sweat evaporates off your body, that cools down your body and both the blood to the skin and the sweat that you produce, the evaporative cooling, is going to cool down your body and return the body temperature back to its set position. There we go.

When the body temperature rises above the set point, how will the body respond?

• A. Shivering
• B. Increased glucagon signaling
• C. Sweating
• D. Reducing blood flow to the skin

While waiting for a bus on a very cold winter day, your body temperature starts to drop. Specialized cells in your preoptic area (POA) of the hypothalamus register a drop in your internal body temperature. Cells in the hypothalamus integrate that information and activate nerve cells that cause muscles around the blood vessels leading to the skin and extremities to contract. When these muscles contract, less blood flows to the skin and extremities. What is the effector in this scenario?

• A. The specialized cells in the POA of the hypothalamus that detected the change.
• B. The muscles of the blood vessels that limited blood flow to the skin and extremities. 
• C. The internal body temperature as measure by the cells of the POA.
• D. The hypothalamus that integrated input and output.

Here’s what students ask on this topic:

What is a negative feedback loop in physiology?

A negative feedback loop in physiology is a mechanism that helps maintain homeostasis by returning a physiological variable to its set point. It involves three main components: receptors, control centers, and effectors. Receptors detect changes in the internal environment, such as temperature or blood calcium levels. The control center, often part of the nervous or endocrine system, processes this information and sends signals to effectors. Effectors then enact responses to counteract the initial change, thereby restoring the variable to its set point. This process opposes the direction of the stimulus, ensuring stability within the body.

How does thermoregulation work as a negative feedback loop?

Thermoregulation is a negative feedback loop that maintains body temperature. Temperature-sensitive cells in the hypothalamus act as receptors, detecting changes in blood temperature. If the body is too hot, the hypothalamus signals sweat glands to produce sweat, which cools the body through evaporation. It also causes vasodilation, increasing blood flow to the skin to release heat. If the body is too cold, the hypothalamus triggers shivering in skeletal muscles to generate heat and causes vasoconstriction, reducing blood flow to the skin to retain heat. These responses help return body temperature to its set point.

What are the components of a negative feedback loop?

A negative feedback loop consists of three main components: receptors, control centers, and effectors. Receptors detect changes in a physiological variable and send this information to the control center. The control center, often part of the nervous or endocrine system, processes the information and determines the appropriate response. It then sends signals to effectors, which carry out actions to counteract the initial change and restore the variable to its set point. This mechanism helps maintain homeostasis by opposing the direction of the stimulus.

Can you provide an example of a negative feedback loop involving blood calcium levels?

An example of a negative feedback loop involving blood calcium levels includes the parathyroid glands. When blood calcium levels are low, the parathyroid glands act as receptors and control centers. They detect the low calcium levels and release parathyroid hormone (PTH). PTH acts on bone tissue, the effector, stimulating it to release calcium into the bloodstream. This increases blood calcium levels, restoring them to the set point. Once the levels are normalized, the release of PTH decreases, completing the negative feedback loop.

What role do the nervous and endocrine systems play in negative feedback loops?

The nervous and endocrine systems play crucial roles in negative feedback loops by acting as control centers. The nervous system quickly processes information and sends rapid signals to effectors, making it ideal for immediate responses, such as thermoregulation. The endocrine system, on the other hand, releases hormones that travel through the bloodstream to target organs, providing longer-lasting effects. Both systems work together to maintain homeostasis by processing information from receptors and coordinating appropriate responses through effectors.