Hi. It’s Mr. Andersen and today I’m going
to go a little bit deeper into feedback loops and talk about the elements of a feedback
loop. You hopefully know the difference between negative and positive feedback loops. And
you could list a few like thermoregulation and blood glucose. We’ll add blood calcium
as we go throughout the year. And there’s a number of feedback loops that control both
inside of us and the outside of us. But I want to talk about the elements. The important
elements of a feedback loop so you’re comfortable with them. And so if we think of us as a system
we’re constantly getting input. And we’re constantly giving output. But that’s not a
feedback loop. A feedback loop doesn’t really exist until we take that output and that actually
feed backs into the system. And so until we have a loop then we really don’t have a feedback
loop. So what we’re looking for are loops. Now the terms should also be familiar with.
In other words you should understand what a receptor is and what an effector is. What
a stimulus is and what a response is. And if you’ve looked at any of the feedback loops
in our book, you’ll start to realize that they have a similar pattern. In other words
the receptor is always going to be in the middle. And then you’re going to kind of have
a figure eight like this. So we’re going to have a figure eight. What happens if it goes
up to high? What happens if it goes too low? And so the receptor will always sit in the
middle. And then the effector is going to sit at the top. And the other effector is
going to sit at the bottom. And so if we look at these definitions, receptor and effector,
they’re organs. And so those are things. Physical things. So the receptors and the effectors
are going to be the top and the bottom of the figure eight. And then these are actions.
And so the stimulus and the response and the stimulus and the response. So let’s put some
arrows like this. Those are going to be actions on either side. In other words what it does
or what it sends or what it’s doing. And so those are the elements of the feedback loop.
And so not only should you know negative – positive. You should be able to say what’s the receptor.
What’s the effector? What’s it doing? How’s it working. And so let’s try that with a little
bit of practice. And so the example I give you as far as feedback loops go is one of
these speed signs. And so when you see a speed sign, then if you’re going to fast you may
slow down. And if you’re going to slow you may speed up. And so let’s define some of
the receptor and the effector. And so let’s do our little, let me get a color here. And
so I’m going to put a receptor in the middle. Now I could do a couple of feedback loops.
But let’s just deal with the person. And so what’s the receptor? Let’s say the receptor
is going to be your eye. It’s going to be in the middle. What is an effector? Let’s
say a foot up at the top and let’s say your foot down here below. So if I say those are
the organs. So we’re going to put an eye, a foot and a foot at the bottom. So this is
going to be my receptor and this is going to be my effector on either side. And so if
we talk about specifically what the stimulus is, well let’s say the stimulus is that you’re
going, I don’t know, we’ll say 38 miles an hour, what’s going to be your response. Your
response is going to be slow down. Let’s say that you’re all of a sudden going 22 miles
an hour. So that’s going to be the stimulus. What’s going to be the response? You’re going
to speed up. And so that will feedback to the eye. And so what we’re going to have is
a feedback loop that’s constantly going up here and then down here and then up here.
But it’s kind of keeping you close to that set point of that speed that we want it to
be. And so we have a negative feedback, negative feedback and it’s kind of keeping you in that
little center point. The example that your book constantly talks about or all science
books talk about is a thermostat. And it’s a great example. And so if we talk about how
a thermostat keeps a room warm, well the thermostat, so what are the nouns? What are the organs
in this case? The thermostat is going to be the receptor. So we’re going to put that right
in the middle. We’re going to have a furnace which is going to be an effector. And then
we’d have another furnace up here. So let’s say that the temperature goes to high. So
if the temperature goes to high, what is the furnace going to do? The furnace is going
to turn off. Let’s say the temperature goes too low. So that’s an action, or a stimulus.
What’s our response going to be? Then it’s going to turn on. And so those are just analogies.
Ways that you can understand how a feedback loop works. But remember we’re going to put
the receptors and the effector and the top, the bottom and right in the middle. And so
that keeps us close to a set point. Now let’s try to do some real ones in biology. So let’s
try and do thermoregulation. So thermoregulation. So we’ve got rid of their definitions over
here. So we’re going to put the receptor in the middle. So the receptor in this case is
called the hypothalamus. Hypothalamus is going to be an organ. It’s actually it a little
bottom part of the brain that drips down from the brain. A lower portion of the brain. It’s
connected to the pituitary. But the hypothalamus is going to sense your temperature. So it’s
a organ. And so let’s start with a receptor right here in the middle. And you may want
to start with temperature. Okay. So let’s say we get too hot. So let’s say that our
stimulus is the hypothalamus is getting too hot. What are some effectors that we could
put at the top? Well one example would be like sweat glands. What’s another one? Capillaries,
like that. My handwriting is not great. So let’s say the temperature goes too high. Our
organs at the top could be sweat glands, capillaries. So if it goes too hot what are the sweat glands
going to do, what’s their response? Well they’re going to sweat. And that through evaporative
cooling is going to lower our temperature. What are the capillaries going to do? If they
get too hot then they’re going to dilate. So there’s more blood going by the surface
of your body. And so that’s going to release more heat. And so that’s going to lower our
temperature as well. And so our response is going to depend on what the effector is. Let’s
say that our temperature goes too low. What are some things that could act down here.
Well capillaries again. So if capillaries before were dilating when we get too cold
then they’re going to constrict. And so what that’s going to do is hold more of your temperature
close to the body. What’s another one? Your muscles for example. Our muscles could eventually
start to shiver. And that’s going to generate a little bit of heat. We could have goose
bumps where it holds our hair up on end which doesn’t really do much if you don’t have a
lot of hair. It’s not like a dog. But it does kind of pull your skin in tight like a coat
pulling it tight. It’s going to hold more of that heat. And so this is our characteristic
feedback loop where if it goes too high we do these things. If it goes too low we do
these things. And so that keeps our body temperature near that set point right in the middle. Another
example is blood glucose. So blood glucose, if we think about that we should maybe set
up the organs first. And so what would the organ be in the middle? Well the organ is
going to be the pancreas. So the pancreas, let’s put that right in the middle. What are
we going to have if our blood glucose goes too high? Well remember, the way I always
do it is that we’ve got beta cells at the top. And alpha cells at the bottom. Now what
are those? Well inside the pancreas, if we say the pancreas looks, it doesn’t look anything
like that. But the beta cells are going to be speckled over the surface of the pancreas.
They’re parts of what are called the islet of langerhans. And then we’re going to have
alpha cells as well speckled around here. So they’re sensing the blood glucose level.
If the blood glucose level goes too high, then what is our response? Well the beta cells
are going to secrete insulin. And so what does the insulin do? Insulin is going to hit
insulin receptors on your cells. It’s going to open up these glucose transports. And glucose
is going to start coming into the cell. Let’s say it goes too low, so if it goes too low,
so this would be our stimulus. What’s going to happen? We’re going to release something
called glucagon. And what glucagon is going to do is it’s going to trigger the liver to
breakdown glycogen into glucose and then release that into the cells. And so we’ve got this
great feedback loop which is going to keep our blood glucose levels about perfect. Why
is it important that we keep our blood glucose levels perfect? It’s because glucose is the
fuel. And if we can’t get that fuel to our cells, or if we use too much of it too quickly,
then we’re out of luck. And so the whole thing is built on this feedback loop where we constantly
are keeping ourselves close to that set point as far as blood glucose level goes. But remember
the whole thing, let’s find a different color, is tied around these organs in the middle.
So the receptors and the effecters. And then the stimulus and the response. And so when
you ever see one of these figure eight diagrams in a book or anywhere, always be thinking
back to the wonderful elements of a feedback loop. Nouns. Actions. Organs. Actions. And
I hope that’s helpful.