02 Reproduction in Lower and Higher Animals - part 13 - Parturition and Lactation

02 Reproduction in Lower and Higher Animals - part 13 - Parturition and Lactation


Parturition: 
  • Humans are viviparous, as they give birth to their young ones. 
  • Parturition is the process of giving birth to a baby. 
  • The physical activities involved in parturition like uterine and abdominal contractions, dilation of cervix and passage of baby are collectively called labour. 
  • Labour is accompanied by localised sensation of discomfort or agony called labour pains. 
  • Parturition is controlled by a complex neuroendocrine mechanism. Signals arise from the fully formed foetus and placenta cause mild uterine contractions. 
  • It is acompanied by rise in estrogen- progesterone ratio, increase in oxytocin receptors in uterine muscles.
  • They cause vigorous contractions of myometrium of uterus at the end of pregnancy. 
  • The fully developed foetus gives signals for the uterine contractions by secreting Adrenocorticotropic Hormone (ACTH) from pituitary and corticosteroids from adrenal gland. 
  • This triggers release of oxytocin from mother's pituitary gland, which acts on uterine muscles of mother and causes vigourous uterine contractions. 
  • This leads to expulsion of the baby from the uterus. 
  • It involves the following three steps : 
1. Dilation stage :

  •  Uterine contractions begin from top, forcing the baby towards the cervix. 
  • Contractions are accompanied by pain caused by compression of blood vessels. 
  • Oxytocin induced uterine contractions become stronger and stronger due to stimulatory reflex. 
  • As the baby is pushed down in the uterus, its head comes to lie against cervix. 
  • Cervix gets dilated. 
  • The vagina also shows similar dilation. 
  • This stage of labour can normally last upto few hours. It ends inrupturing of amniotic membrane of foetus.

2. Expulsion stage : 

  • The uterine and abdominal contractions become stronger. 
  • In normal delivery, the foetus passes out through cervix and vagina with head in forward direction. 
  • It takes 20 to 60 min. The umbilical cord is tied and cut off close to the baby's navel. 
3. After birth : 

  • After the delivery of the baby the placenta separates from the uterus and is expelled out as "after birth", due to severe contractions of the uterus. 
  • This process happens within 10 to 45 minutes of delivery.


Lactation: 

  • The mammary glands of the female start producing milk at the end of pregnancy by the process of lactation. 
  • Prolactin is the hormone which is responsible for production of milk. 
  • Lactation helps the mother in feeding the new born baby. 
  • The fluid secreted by the mammary glands soon after child birth is called colostrum. 
Colostrum: 

  • It is the sticky and yellow fluid secreted by the mammary glands soon after child birth. 
  • It contains proteins, lactose and mother's antibodies e.g. IgA. 
  • The fat content in colostrum is low. 
  • The antibodies present in it helps in developing resistance for the new born baby at a time when its own immune response is not fully developed.



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