Homeostasis Worksheet
In negative feedback systems, the response reverses a change in a controlled condition
In positive feedback systems, the response strengthens the change in a controlled condition.
State whether each of the following indicates negative or positive 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, a
signalissenttothebrainwhichinturnslowsdownthebody’sheartrate. 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.
