Question

Case:
The average duration of human pregnancy is about 9 months. Parturition in humans is induced by a complex neuroendocrine mechanism. Rekha has completed her 9 months of pregnancy and her expected delivery date has passed but she has not undergone labor. Both her and family got worried and went to the hospital to consult her obstetrician. A complete blood work was done and the doctor observed extremely low levels of certain hormones and high levels of hPL, estrogen, thyroxine, etc.
On further examination, the doctor revealed that her uterus is not showing vigorous contractions which are extremely needed for delivery of the foetus. The doctor took consent from Rekha and injected her with a medicine to promote uterine contractions. Also, her obstetrician counselled her about benefits of breast feeding and good practices for postnatal care of herself and the baby.

During parturition, the hormone released from maternal pituitary acts on uterus and causes strong uterine contractions which in turn stimulate further secretion of this hormone. This is a type of:
[0.7 mark]

• A. Positive feedback mechanism
• B. Negative feedback mechanism
• C. Allosteric modulation
• D. Competitive inhibition

Answer 1

The correct option is A Positive feedback mechanism

The release of oxytocin from the maternal pituitary gland during labor is an example of positive feedback mechanism. Parturition is induced by a complex neuroendocrine mechanism. The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin.