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.