Say whether each loop is a negative feedback or a positive feedback…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Say whether each loop is a negative feedback or a positive feedback.
- A high level of thyroid hormones switches down the release of TSH.
- Oxytocin makes the uterus contract, and the contractions release more oxytocin.
- A high blood glucose releases insulin, which lowers the glucose.
- A low blood calcium releases PTH, which raises the calcium.
- Which of these loops is ended by an event outside the loop, and what is the event?
Need a reminder? The key ideaShow
Negative feedback keeps a level near a set point. Positive feedback drives a process to its end, as oxytocin does in childbirth. Insulin and glucagon, and PTH and thyrocalcitonin, work in opposite ways. The hypothalamus joins the nervous system to the endocrine system.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Negative.
Step 2. (b) Positive.
Step 3. (c) Negative.
Step 4. (d) Negative.
Step 5. (e) Loop (b). The contractions and the oxytocin grow until the birth of the baby ends the loop.
Answer: (a), (c) and (d) are negative; (b) is positive; (e) the labour loop, ended by the birth.
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