For each scenario in the attached handout write down whether the scenario is positive or negative feedback.

1. If blood temperature rises too high,

specialized neurons in the hypothalamus of the brain sense the change. These

neurons signal other 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.

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.

3. 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.

4. During childbirth stretching of the uterus

triggers the secretion of the hormone oxytocin, which stimulates uterine

contractions and speeds up labor.

5. The walls of arteries stretch in the

presence of high blood pressure. Baroreceptors located in these walls also

stretch and as a result, asignal is sent to the brain which in turn slows down the

body’s heart rate. This slows the flow of blood through the arteries causing less

pressure. As BP drops the baroreceptors become flaccid and a signal is sent to

speed up the heart rate.