Homeostasis

Homeostasis is the process of keeping everything in the body functioning at normal levels. Put another way, it is regulating the internal environment in response to changes in the external environment. This implies two main ideas:

There are normal "levels" for body processes.
- Body temperature is around 98.6 degrees F.
- Blood sugar is around 90 mg/dL
- You have enough muscle tissue to perform all of your daily activities.
You have a control system that monitors, processes and responds when these levels are out of the normal range.
- The nervous system can detect body temp above 98.6 and turn on sweat glands to cool it down.
- The pancreas can detect low blood sugar and release a hormone called glucagon to bring it back up.
- If you start to work out regularly, your nervous system gains greater control of your muscles and hormones can stimulate the formation of new blood vessels and muscle tissue.

No matter which system is used, maintaining homeostasis involves the use of Feedback.

Negative is Good, Positive is...

Feedback is a way to evaluate and respond to a stimulus. There are two general types of feedback that occur in the body: Negative and Positive.

Negative Feedback produces a response that is opposite to the change in the stimulus so that it stays within a normal range.

Body Temperature

When the body is hot, one starts to sweat which cools the body down.
When the body is cold, one starts to shiver which burns energy and warms the body.

Blood Sugar

When blood sugar is high, insulin is released that causes the liver to build glycogen, thus removing it from the blood.
When blood sugar is too low, glucagon is released that causes the liver to break glycogen down and release glucose into the blood.

Positive Feedback amplifies the change until a critical point is reached, which is usually, but not always, a good thing.

Blood Clotting

A broken blood vessel stimulates platelets to stick to each other at the site of the injury.
Sticky platelets cause other platelets to become sticky, which then signal other platelets to become sticky and so on.
When the bleeding is stopped (critical point) the platelets stop signaling others to become sticky.

Childbirth

When a fetus reaches full term, it creates pressure on the wall of the uterus which stimulates the hypothalamus to release the hormone oxytocin.
Oxytocin causes the uterus to contract, creating more pressure which stimulates the release of more oxytocin causing greater contractions, more pressure and more oxytocin.
Once the baby is born (critical point), there is no more pressure, no more release of oxytocin, and no more contractions.

Psychology - behaviors in a positive feedback loop can often lead to negative consequences.

Anxiety about a test can lead to more worrying and wasting time instead of preparing or studying, thus increasing the anxiety. Eventually, the test happens (critical point) and there is no more need to worry about that event.