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- [Voiceover] Here I'm
looking at different parts,

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different things in the
body, with feedback,

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so we talk about those body systems

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and the cavities that can fit with them,

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but how does your heart know

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to speed up or slow down?

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How does your body know to
sweat because you're hot?

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All these are feedback loops.

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Basically what a feedback loop is,

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there's either a positive
or a negative feedback loop.

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In this case we're looking
at the negative feedback.

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In the case of a negative
feedback, there's a stimulus.

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Something is happening
that is not to norm.

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For example, if you walk
outside in the middle of winter,

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and it's zero degrees out,
you're not going to feel warm,

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you're going to feel cold.

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It's that cold temperature

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that's going to trigger
receptors in your body,

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thermal receptors,

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so that's the stimulus.

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The stimulus with the cold.

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Then sensor are the receptors.

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They then will go and control an effector,

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which will be your body shivering,

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because you're going to want to warm up,

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so pretty much your body
is controlled mostly

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by negative feedback loops,

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and these negative feedback
loops are always the same way,

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they're always the same four basic parts,

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stimulus, a sensor that
picks up the stimulus,

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a control mechanism that will
make a change in your body,

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and that causes an effect
to put you back to normal.

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I've already used a great example

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is going to be temperature.

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It doesn't matter if it's hot or cold.

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I give you an example of
cold, on the screen here,

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you can see hot,

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but always something is
going away from the normal,

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and this whole negative feedback

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is trying to maintain homeostasis.

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Homeostasis is what your
body's trying to do.

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It' trying to stay at a set level,

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so you're not trying to
get too warm or too cold.

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You want to say at a comfortable level,

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but sometimes there's also
positive feedback loops

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in your body.

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The example shown here
is normal childbirth.

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When it's time for birth,

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the body will initiate
a positive feedback loop

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so what'll happen here,

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is as the body is getting
ready to give birth,

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oxytocin, a hormone is being
carried in the blood stream.

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The oxytocin will initiate
uterine contractions.

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As the uterine contractions continue

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and the baby's head pushes
against the cervix more,

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more and more oxytocin
keeps getting released.

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More oxytocin means more contractions,

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and it's like constant feedback.

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The stronger the contraction,
the more oxytocin.

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The more oxytocin, the
stronger the contraction.

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It'll eventually cease and
stop, once the baby is born.

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Then, after that's
done, it can return back

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to normal homeostasis, but as
long as the positive feedback

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is going, it'll keep changing
away from the normal,

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to cause this positive response.

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In this case you might say
contractions are positive,

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but the ultimate result
childbirth, is a positive response,

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but the body itself for all we know about,

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we know a lot and so much

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because of all the
different medical imaging,

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and technology we have.

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I mean X-Rays have come a long way.

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An X-Ray now can show hairline fractures.

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It can show great detail in the bones,

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but when they first started,

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it was a very rudimentary, very crude way

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of taking a radioactive isotope in a box,

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and putting a hand or a limb over it,

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with extra paper on the other side.

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It wasn't even.

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It wasn controlled.

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It wasn't anything like the
images you can see today,

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so medical imaging has come
a long way to help out.

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It's not just X-Rays, you have CT scans.

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You can go in for MRIs,

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you have even PET scans,

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and finally ultrasounds,

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can be used for a huge range of things.

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It's not just ultrasound for pregnancy,

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but ultrasound can be used for other

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different aspects as well.

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They can monitor different glands,

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like a thyroid gland can be
monitored through ultrasounds,

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so there's tons of various medical imaging

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that can help see different
aspects of our body,

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from the heart tissue, bone,
to the very soft tissue,

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blood flow, or brain tissue,

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so there's a lot of things that
are going on with our body,

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but also they've seen around society.