2.6 Parturition and lactation

. Parturition and lactation Parturition is the completion of pregnancy and giving birth to the baby. The series of events that expels the infant from the uterus is collectively called “labour”. Throughout pregnancy the uterus undergoes periodic episodes of weak and strong contractions. These contractions called Braxton-Hick’s contractions lead to false labour. As the pregnancy progresses, increase in the oestrogen concentration promotes uterine contractions. These uterine contractions facilitate moulding of the foetus and downward movement of the foetus. The descent of the foetus causes dilation of cervix of the uterus and vaginal canal resulting in a neurohumoral reflex called Foetal ejection reflex or Ferguson reflex . This initiates the secretion of oxytocin from the neurohypophysis which in turn brings about the powerful contraction of the uterine muscles and leads to the expulsion of the baby through the birth canal. This sequence of events is called as parturition or childbirth . XII Std Biology-Zoology Chapter- XII Std Biology-Zoology Chapter- Human Reproduction Weeks Formation of foregut, midgut and hindgut. Heart starts functioning. Forebrain is most prominent. Upper limbs appears as paddle-shaped buds Weeks Limbs and digits fully formed. Movements start taking place. Neck appears between head and thorax. External genitalia show sex differences Weeks Eyes and ears are well defined. Ossification of long bones are seen Urine formation begins Weeks Lower limbs reach final development. Movements are seen Weeks Length of foetus increases Hair on the head and eyebrows. Skin becomes covered with sebaceous gland Weeks Lungs are well developed Rapid eye movements begin. Foetus starts gaining weight Weeks Immune system starts developing. Central nervous system developed. Retina is well developed Weeks Body weight increases rapidly. Skin is smooth due to deposition of subcutaneous fat Weeks Blood vessels are completely developed. Baby is positioned into the pelvis in head down position