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.
Always graph time on the horizontal (X) axis. Label your axes
Problem 1: A patient’s body temperature was recorded over a 24-hour period; the temperature at each hour is listed in the table below. Graph the data in the space provided and state whether it indicates negative or positive feedback.
TIME TEMP, °F 12 am 98.30 3 am 98.10 6 am 98.40 9 am 98.90 12 pm 98.70 3 pm 98.50 6 pm 98.60 9 pm 98.80
TYPE OF FEEDBACK _____________negative____________________________________
Problem 2: A man with heart disease has his blood pressure monitored closely.
TIME BP mm Hg 7 am 200 8 am 190 9 am 170 10 am 150 11 am 130 12 noon 110 1 pm 70
TYPE OF FEEDBACK __________________positive_______________________________
Recognize normal parameters:
The normal range for blood glucose is 70-110 m/dl
The normal range for blood pH is 7.35-7.45
Problem 3: A woman is being tested for diabetes mellitus. Her blood glucose is measured over a period of time.
Blood Glucose m/dl 0 100 1 hour later 120 2 hours later 110 3 hours later 90 4 hours later 80 5 hours later 85
TYPE OF FEEDBACK _________________negative_____________________________
Does the patient always remain within the normal range ____no_____________
Does the patient have any apparent problems with glucose regulation? _______yes________
Problem 4: A man with kidney problems is being watched for acid base imbalance.
TIME pH 7 am 7.45 9 am 7.46 12 pm 7.44 1 pm 7.42 6 pm 7.39 8 pm 7.37 10 pm 7.38 12 am 7.40 3 am 7.42
TYPE OF FEEDBACK ____________positive__________________________________
Does the patient always remain within the normal range __________yes_______
Does the patient have any apparent problems with acid base balance? ____no___________