Positive and Negative Feedback Loops

Negative Example 4

*Body temperature increases - cooling mechanism activated (sweating) - body temperature decreases *Body temperature decreases - Heating mechanism activated (shivering) - body temperature increases

Positive

Amplification (away from target) - fruit ripening, child birth, blood clotting The response strengthens the change in a controlled condition.

Positive Example 2

During childbirth stretching of the uterus triggers the secretion of the hormone Oxycontin, which stimulates uterine contractions and speeds up labor.

Negative Example 1

If blood temperature rises too high, specialized neurons in the hypothalamus of the brain sense the change. These neurons signal the nerve centers, which in turn send signals to the blood vessels of the skin. As these blood vessels dilate, more blood flows close to the body surface and excess heat radiates from the body.

Negative Example 2

If the blood temperature falls too low, specialized neurons in the hypothalamus of the brain sense the change and signals are sent to the cutaneous arteries (those supplying the skin) to constrict them. Warm blood is then retained deeper in the body and less heat is lost from the surface.

Positive Example 1

Part of the complex biochemical pathway of blood clotting is the production of an enzyme that forms the matrix of the blood clot. This has a self-catalytic, or self-accelerating effect, so that once the clotting process begins, it runs faster and faster until, ideally, bleeding stops.

Negative

Stabilization (keep at target) - Temperature regulation The response reverses a change in a controlled condition

Homeostasis

Stable internal balance

Negative Example 3

The walls of arteries stretch in the presence of high blood pressure. Baroreceptors located in these walls also stretch and as a result, a signal is sent to the brain which in turn slows down the body's heart rate. This slows the flow of blood though the arteries causing less pressure. As BP drops the baroreceptors become flaccid and a signal is sent to speed up the heart rate.

Feedback Loop

cause and effect body system(s) respond