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. _______________Negative_________________ 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. _____________Negative___________________ 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. ___________Positive_____________________ 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. ___________Positive_____________________ During childbirth stretching of the uterus triggers the
secretion of the hormone oxytocin, which stimulates uterine contractions and speeds up labor.
5. ________Negative________________________ 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 through the arteries
causing less pressure. As BP drops the baroreceptors become flaccid and a signal is sent to speed up the
heart rate.
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. _______________Negative_________________ 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. _____________Negative___________________ 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. ___________Positive_____________________ 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. ___________Positive_____________________ During childbirth stretching of the uterus triggers the
secretion of the hormone oxytocin, which stimulates uterine contractions and speeds up labor.
5. ________Negative________________________ 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 through the arteries
causing less pressure. As BP drops the baroreceptors become flaccid and a signal is sent to speed up the
heart rate.
