Read the given passage and answer the following questions :
The average duration of human pregnancy is about 9 months which is called the gestation period. Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus. This process of delivery of the foetus (childbirth) is called parturition. 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. The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions. This leads to expulsion of the baby out of the uterus through the birth canal – parturition. Soon after the infant is delivered, the placenta is also expelled out of the uterus. The mammary glands of the female undergo differentiation during pregnancy and starts producing milk towards the end of pregnancy by the process called lactation. This helps the mother in feeding the new- born. The milk produced during the initial few days of lactation is called colostrum which contains several antibodies absolutely essential to develop resistance for the new-born babies. Breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.
The complex neuroendocrine mechanism that induces parturition involves which of the following hormones?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Cortisol, estrogens and oxytocin
Parturition (childbirth) is started by signals from the fully developed foetus and the placenta. These signals act through a neuroendocrine mechanism, in which nerve signals and hormones work together. NCERT names three hormones in it: cortisol, estrogens and oxytocin. Oxytocin causes the strong uterine contractions that push the baby out.
Option (1) Estrogens, prolactin and oxytocin — Incorrect. Estrogens and oxytocin are part of the mechanism, but prolactin is not. Prolactin is linked with the growth of the mammary glands and the formation of milk, not with starting childbirth.
Option (2) Cortisol, hPL and oxytocin — Incorrect. Cortisol and oxytocin are correct, but hPL (human placental lactogen) is a hormone of the placenta that supports pregnancy. The book does not name it in the mechanism of parturition.
Option (3) Cortisol, estrogens and oxytocin — Correct. The mechanism that induces parturition involves cortisol, estrogens and oxytocin. All three hormones of this option are the ones NCERT lists.
Option (4) Cortisol, progestogens and thyroxine — Incorrect. Progestogens and thyroxine rise during pregnancy and help maintain it, but they do not induce parturition. This set also leaves out oxytocin, the hormone of the uterine contractions.
Note: The full list of hormones for parturition sits in the chapter Summary, not in the main paragraph. The Summary is short, so there is no excuse to skip it.
NCERT Extract:
Summary – “… The zygote undergoes repeated mitotic division to form a blastocyst, which is implanted in the uterus resulting in pregnancy. After nine months of pregnancy, the fully developed foetus is ready for delivery. The process of childbirth is called parturition which is induced by a complex neuroendocrine mechanism involving cortisol, estrogens and oxytocin. Mammary glands differentiate during pregnancy and secrete milk after child-birth.”