Feedback Loops: Negative Feedback - Video Tutorials & Practice Problems
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Negative Feedback Loops
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Now we're gonna 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 gonna 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 gonna be important going forward. So keep that in mind. So let's now break down these different components. So there's gonna be three main components to a negative feedback loop. First up, we have the receptor, the receptor is gonna measure the stimulus and by stimulus, we just mean whatever variable we're talking about it's gonna change. And that's gonna be that 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. Ok. 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 going down to his collar bone. 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, measuring a physiological variable. In this case, the calcium level in the blood and it recognizes that blood calcium is too low. So it's gonna 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 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 gonna 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 gonna 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. Ok. 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 gonna practice that some more going forward and I'll see you there.
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example
Feedback Loops: Negative Feedback Example 1
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This example asks us to identify the components of a negative feedback loop. All right. So you stand up quickly causing your blood pressure to fall and you feel lightheaded, 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 an effector. OK. 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 uh loop going, it starts at the heart and an arrow goes up to the brain stem and then down back 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 gonna be blood pressure falls. All right. Now think what is the response Well, in a negative feedback loop, the response is gonna push in the other direction. And sure enough, we're gonna raise the blood pressure. So that response is gonna be blood pressure rises. OK. Let's look at the different components of the feedback loop over here. Remember we have a receptor control center sometimes called the integration center and the effector. So let's read each one and think how they match up. First up, we have the mela 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 gonna integrate that response and tell the body what to do and how to respond. So the control center, I'm actually just gonna draw a line to the mela and the brain stem right there. Uh The next one we have, it says after standing up quickly barrow receptors above the heart measure a drop in blood pressure. All right. What do you think that sounds like? Well, right there in the name barrow receptors, they are measuring a drop in blood pressure when it measures something that is a receptor. And I'm just gonna 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 gonna 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 uh arrow back up to the heart for that one. OK. With that, we have some more practice problems below and I'll see you in the next video.
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Problem
Problem
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.
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Problem
Problem
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.
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concept
Negative Feedback Loops: Temperature
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4m
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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 gonna worry about the specific for one negative feedback loop. We're gonna talk about temperature. Now, don't worry too much. You probably know a lot of the details about thermoregulation 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 to the components. Like we've been practicing, we have first the receptors, the receptors in this case are gonna be the temperature sensitive cells of the hypothalamus. The hypothalamus is a region in your brain. As blood goes up in 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 gonna 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 gonna 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 gonna 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 a dripping sweat because it's hot outside. Our next effector is gonna 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 gonna 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 the thermo receptors in the brain are gonna recognize that they're gonna send a message to the control center, the hypothalamus, the control center is gonna integrate that information and send a message to the effectors and the effectors are gonna respond the skeletal muscles and the smooth muscles, the skeletal muscles are gonna start shivering. And when you shiver, the movement of muscles generates heat. So that shivering, those muscle contractions are gonna increase your body temperature. The blood flow to the skin is gonna decrease and we're gonna 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, skin are gonna 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 gonna be cold because it's cold outside. So you want to keep that, that blood on the inside of your body deep inside your body, that also is gonna raise your body temper. So those two things together are gonna push back against the stimulus and return your body temperature to normal. Now, when your body gets too hot, same thing you can imagine our meter here, it's going off into the red. While the receptors in the brain, the thermo receptors in the brain are gonna recognize that they're gonna send a message to the control center. And the hypothalamus, hypothalamus is gonna 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 gonna call this vaso dilation. The blood vessels to the skin baso blood vessels are gonna dilate, they're gonna get bigger around. Meaning more blood is gonna go to the skin as the blood is close to the skin, it's gonna get cooled by that evaporative cooling from the sweat and your temperature again is gonna 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 vessel, more blood in the blood vessels close to the skin. All of that together is gonna push back against the original stimulus and it's gonna cool the body. Ok? With that, we have some practice problems below and I'll see you in the next video.
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example
Feedback Loops: Negative Feedback Example 2
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2m
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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 when 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 gonna 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, right? Why do you get a red face when you get too hot? A red face, you're shunting blood to the skin and we call that vaso dilation of the blood vessels to the skin. And that specific word vasodilation. Uh 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. Ok. 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 gonna cool down your body and return the body temperature back to its set position. There we go.
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Problem
Problem
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
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Problem
Problem
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.
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