Homeostasis [1]: Negative feedback (A Level Biology)


Uploaded by freeeschool on 01.09.2012

Transcript:
A Level Biology: Homeostasis 1 – Negative Feedback
Hi! Welcome to the first of our videos about Homeostasis. Today, we are going to be looking
primarily at how homeostasis works.
First of all, when I’m talking about homeostasis, you need to know that homeostasis is all about
balance. Basically, homeostasis means “staying the same”. It was a term introduced by this
guy, Claude Bernard. So when we are talking about homeostasis, we are basically defining
it as maintaining a constant internal environment. The internal environment can be anything from
the content of a unicellular organism to plants and also to animals.
What I would like you to do is I would like you to think about the last time you did some
exercise; or better yet, jog on the spot now for say,
roughly 60 seconds. I want you to make note of what processes or what experiences your
body goes through. Depending how fit you are, you should find that after a couple of seconds,
your breathing rates and also your skin temperature should start to increase. As your body begins
to work more, it is going to need more oxygen for respiration; likewise, it is going to
be producing more carbon dioxide which it needs to get off as well.
It is also going to be producing a lot more heat. When you stop exercising, you should
find that over time, your breathing rate gradually starts to fall again until you are right around
your normal breathing rate or your resting breathing rate.
Basically, it follows a simple loop. You’ve got a change in the environment which is detected
by a receptor. The receptor then sends a signal to the control center. The control center
then decides on a particular response. It then sends a signal to an effector. After
receiving the signal, it tries to correct the deviation from that stable internal environment
by either enhancing it via positive feedback or by depressing it via negative feedback.
We are going to focus primarily on negative feedback. Here’s our very simple negative
feedback loop. In the middle here, you have our normal; that’s our normal, stable internal
environment. For example, let’s say you suddenly get too hot. Receptors within the
skin detect that change from the stable internal environment. That information is sent to the
control center; that’s usually the hypothalamus. The hypothalamus then sends signals to an
effector; usually glands within the skin to produce sweat and therefore, your temperature
decreases. Likewise, if for some reason you start to feel cold, the receptors in the skin
detect that change; send information to the hypothalamus and your hypothalamus would then
send information to your muscles, for example, to get them to start shivering which will
increase your temperature.
You should be able to define homeostasis. That’s a stable internal environment. You
should also be able to define what I mean by negative feedback and give a simple example.
That concludes our short presentation. I hope you enjoyed it. Don’t forget to keep a lookout
for more videos coming up soon.
[end of audio – 04:21] A Level Biology: Homeostasis 1 – Negative
Feedback Page…1