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Explain the process of parturition. - Biology

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Answer in Brief

Explain the process of parturition.

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Process of Parturition:

1. First Stage (Dilation):

  1. It lasts for about 12 hours.
  2. Regular peristaltic contractions of the uterine wall begin, passing from its top downward.
  3. These contractions move the foetus down towards the cervix which expands fully.
  4. Amnion and chorion rupture.
  5. The amniotic fluid passes out, lubricating the vagina.
  6. The foetal placenta is pulled out from the uterine wall, making the baby free.

2. Second Stage (Expulsion):

  1. It lasts for about 20 minutes to one hour. The uterine contractions become more powerful and are accompanied by contractions of the abdominal wall.
  2. With these contractions, the baby is gradually pushed outward through the dilated cervix and vagina, with the head foremost, and is finally “delivered” (born) out of the cervix.
  3. The umbilical cord is ligatured at two places close to the baby and cut between the ligatures. This frees the baby totally from the mother. Cervix and vagina are dilated and the ligaments of the pelvic girdle are relaxed by the hormone relaxin from the corpus luteum for easy birth of the baby.

3. Third (Placental) Stage:

  1. It lasts for just 10-45 minutes after the infant’s birth. Now, the placenta, umbilical cord and foetal membrane are expelled by a series of uterine contractions. These structures are referred to as the “after birth”.
  2. Further contractions of the uterus close the cervix and prevent excessive bleeding. Bleeding, throughout the process, is kept low by the contraction of smooth muscle fibres of uterine blood vessels supplying the placenta.
Concept: Parturition (Birth) in Human
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