HOMEOSTASIS (Negative and Positive Feedback)
Homeostasis is the maintenance of your internal environment. It is the
reason why you can be outside when it's below freezing, and also when
it's 100 degrees out. Your body uses control mechanisms and feedback
to keep your internal systems functioning.
Feedback loops are a big part of maintaining homeostasis as well.
Negative feedback loops- counteracts change
Positive feedback loops- increases change
Positive feedback works with a stimulus while negative feedback
works against a stimulus.
An example of positive feedback is oxytocin being released as a mother
gives birth. The hormone increases the contraction of the cervix until
the baby is born.
Negative feedback is your body shivering when you are cold. It is
working against the cold by producing more heat.
For example, when it's hot outside, you start to sweat. Why? Sensors in
your body "discover" a change in temperature. These sensors alert
your control center, or your brain. Your brain compares your current
temperature to where your temperature should be (set values) to
survive. If your temperature falls above (or below ) these set values, it
sends a message to your communication system (your nervous and
endocrine system). Your communication then sends a message (a nerve
impulse or hormone) in response to counteract (or increase in
positive feedback) the change. A target muscle or organ receives the
message and reacts to it.
When your body temperature rises, your skin (the target organ)
receives a message from your communication system telling it to open
its pores and allow sweat to be released. Sweat cools your body
temperature down, or COUNTERACTS the change in temperature. A
person sweating when it's hot out is an example of negative feedback.
POSITIVE FEEDBACK LOOP: [ "A causes B, and B causes A"]
Let's use a dumb analogy as an example. Let's say (A) your brother, who
lives in the next room, is listening to really loud music, I mean the walls
are shaking from the bass, and it's just unreasonably loud. You, who live
in the next room, are trying to study. You (B) react to your brother's loud
music by turning your own loud music up to drown his out. In response,
he turns his up even higher to drown yours out. And this goes on and
on, with each of your responses "driving" or "enhancing" the other.
This is an example of a positive feedback loop. "A causes B, then B
causes A". And the cycle just keeps repeating and the results (e.g.,
volume of music) keep getting more and more amplified. Keep in mind
that the loop does not necessarily have to be composed of only 2 events
(A and B). It is totally possible that A causes B, B causes C, C causes D,
etc., but somewhere down the line "E" or "F" or "G" or "Z" will enhance
"A", thus the cycle will start all over again. This is still a positive
feedback loop.
I'm sure you can think of a good example of how this might happen in
environmental science.
NEGATIVE FEEDBACK LOOP: "A causes B, and B prevents A"
Do you see the difference from Positive Feedback Loop? Instead of
"causing" or "enhancing" a previous event, "B" (or "C" or "D" or "E" or
"Z") is actually inhibiting/preventing the earlier event "A". As an
example, you can think about what happens in your body when you're
hungry and you eat a meal. (A) Your brain tells you that you are totally
starving, so (B) you pour a bowl of cereal and eat it. In response, (C)
your blood sugar rises and sends signals to your brain that you are no
longer hungry (A). In this case, the end of the chain of events acts to
"turn off" the signal at the beginning of the chain of events.
Negative Feedback Loop
What type of Feedback is shown below?
Describe 3 types of Negative Feedback and 3 types of
Positive Feedback not mentioned in the above reading.
Negative Feedback:
1)
2)
3)
Positive Feedback:
1)_____________________________________________________
2)_____________________________________________________
3)_____________________________________________________