Answer these questions about the control of birth…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Answer these questions about the control of birth.
- What sends the first signals?
- What name is given to the first mild contractions of the uterus?
- Which gland of the mother releases oxytocin?
- Why is the control a positive feedback and not a negative feedback?
- What happens to the loop after the baby is born?
Need a reminder? The key ideaShow
Parturition: the fully developed foetus and the placenta send signals, the uterus contracts mildly (the foetal ejection reflex), the pituitary releases oxytocin, the contractions become stronger, and more oxytocin is released. This is positive feedback. In a model with a first strength and a gain , the strength after rounds is . The first milk is the colostrum, rich in antibodies. Prolactin makes milk, and oxytocin ejects it.
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) The fully developed foetus and the placenta.
Step 2. (b) The foetal ejection reflex.
Step 3. (c) The pituitary gland.
Step 4. (d) The contractions cause more oxytocin to be released, and the oxytocin makes the contractions stronger. The result makes the cause stronger, so it is a positive feedback.
Step 5. (e) The baby leaves the uterus, the stimulus is gone, and the loop stops. The placenta is expelled soon after.
Answer: (a) the foetus and the placenta; (b) the foetal ejection reflex; (c) the pituitary; (d) the result strengthens the cause; (e) the loop stops.
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