Captions are on! Click CC at bottom right to turn off. You can follow the Amoebas on Twitter (@AmoebaSisters) and Facebook. Did you know, just sitting here right now,
you’re doing something absolutely remarkable? Well you…your cells, tissues, organs, organ
systems---yep we just leveled up those biological levels of organization--- they’re all working
towards something called homeostasis. It’s a state of balance. Yes, homeostasis means many things in your
body: for example, that your blood stays within a certain pH level range. It means your blood glucose remains within
a certain range. It means your internal body temperature stays
within a certain range. See, we’ve mentioned the major body systems
before, and that they work together---and today we’re going to talk about HOW they
work together---using something called positive and negative feedback. And, also, how this relates to homeostasis. So many years ago, I had a pet bearded dragon. Her name was Debbie and she was the best lizard
ever. Debbie used to sit on our couch with me when
I’d watch TV. And she loved to have her chin scratched. I even got her a bearded dragon leash so I
could take her outside…yeah, they make those…anyway, Debbie loved her heat lamp. She would sit under the heat lamp on her rock. And when she got too hot, she would get off
her rock and out of the heat lamp range and go somewhere else. She had a huge enclosure too because, I wanted
Debbie to be a happy lizard, so she could find an ideal temperature. Well why all this talk about Debbie? Well, Debbie is an example of an animal that
some people refer to as cold-blooded. Or a fancier term, ectotherm. We actually like the fancier term a bit better
though, because her blood isn’t necessarily cold. Her body temperature can fluctuate with the
environment But not you. You are warm-blooded, or the fancier term,
an endotherm. Your body works hard to keep the internal
temperature it keeps. It’s also a beautiful example of something
called negative feedback. Before we define it---let us show you this
example. Say you are in an environment that is very
hot. Like…being outside in the Texas summer heat. That’s typically hot. Thanks to nerves which can act as sensors,
the brain notices this. It will send signals to couneract this variable. Sweat glands do what they do best: sweat! Heat is lost as that sweat evaporates off
of your skin. You may have some redness too---that’s because
of your blood vessels are getting wider (dilating)---in order to help get rid of that heat. The result, whether you realize it or not,
helps you lower your body temperature. But wait! What if you now go inside and the AC is blasting. You will stop sweating. You may even shiver. The muscle contractions of shivering can generate
heat. And those blood vessels will now decrease
in diameter size (constrict) to help you conserve the heat because that makes it harder for heat
to escape. Your body temperature can increase then. This is negative feedback. So a simplified definition: negative feedback
is when some variable triggers a counteracting response---in order to come back to some set
point. If we consider that this whole thing is actually
a negative feedback loop, we can see that the negative feedback brings the body back
to the set point, which in this case, is a stable temperature. Keeping homeostasis. Negative feedback is also going on in the
regulation of your glucose (your blood sugar). Ok we’re really simplifiying this here,
as we often do, but when glucose (blood sugar) is too high, one hormone that is released
is insulin. I always imagine insulin as this hormone that
makes the cells say, “FEED ME!” because it has the ability to make cells take in glucose. On the flip side, if glucose is too low in
the blood, a hormone called glucagon can be released. This hormone can have many effects and one
of them is that it can cause the liver to release glucose into the blood. There’s more to the regulation of blood
sugar than this but you can see how that’s negative feedback---you have counteracting
responses here in order to keep homeostasis. So what about positive feedback? Positive feedback is when, instead of getting
a counteracting response to some variable, you instead intensify the variable. Positive feedback can be like “more more
more” instead of “let’s counteract this.” The example that always stuck with me when
I was a student is the example about the human human baby being born. In biology classrooms everywhere, it’s a
classic example. When a human baby is ready to be born, there
is pressure on the cervix. And that pressure and the hormones involved
cause contractions of the uterus---because that’s a big part about how the baby is
going to be born. More release of hormones will equal more contractions
and pressure which will cause more release of hormones. And more release of hormones will mean more contractions
and pressure. Contractions help get the baby out, but it’s
also part of a beautiful illustration of what positive feedback can do. So why do we care about feedback? Other then, you know, the importance of negative
feedback in maintaining homeostasis and the role of positive feedback in many body processes? Well we also need to understand feedback so we can understand what is happening when there is a problem in the feedback systems. One example: perhaps you’ve heard of Type
1 diabetes. It’s a disorder that can mean that your
pancreas, which is an organ that is involved with making some hormones like insulin, is
not working correctly. Insulin is not produced and, because of that,
one issue is that you are not going to be able to get glucose (the blood sugar) into your cells. Glucose outside of the cells cannot be used
in cellular respiration---the cells need to take the glucose IN to make ATP energy in cellular respiration. Therefore, your cells need to be able to take
IN the glucose to survive. So, many Type 1 diabetics need to give themselves
insulin and monitor their blood sugar because the negative feedback may not work as it should. Well, that’s it for the Amoeba Sisters and
we remind you to stay curious!
