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Embryonic Development and Parturition

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Embryonic Development and Parturition - Lesson Summary

The birth of a baby is an intricate and complex process that begins when the zygote undergoes cleavage and develops into a blastocyst – a hollow ball consisting of a trophoblast, an inner cell mass and a cavity called blastocoel. As the trophoblast grows outwards and penetrates the endometrial lining of the uterus, the blastocyst, with a developing embryo, gets implanted in the uterus and pregnancy is initiated.

After implantation, the trophoblast grows further, which causes the blastocyst to sink in and get covered by the cells of the uterus. As the blastocyst sinks further into the uterus finger-like projections called chorionic villi start appearing on the trophoblast. As the chorionic villi grow further, they interlock with uterine tissues to form the placenta – a structural and functional unit between the developing embryo and maternal body. Interestingly, when the placenta begins to form the inner cell mass moves downwards and differentiates to form an embryonic disc consisting of three germ layers – the outer ectoderm, middle mesoderm and inner endoderm. The placenta is an important structure that supplies the embryo with oxygen, nutrients and hormones as well as carries waste products from the embryo back to the mother. The embryo stays inside the uterus for nine months, which is called the gestation period.

The end of the gestation period, the foetus as well as the placenta starts secreting hormones that set in motion mild uterine contractions called the foetal ejection reflex. These contractions, in turn, act on the mother’s pituitary gland that now starts secreting oxytocin, a hormone that causes stronger uterine contractions. The simultaneous uterine contractions and oxytocin release makes the contractions stronger with every passing minute and ultimately results in the expulsion of the baby from the mother’s uterus. This process of delivery of the foetus is called parturition. Immediately, after the birth of the baby, the placenta is expelled from the uterus. Soon after birth, the baby needs to be breastfed by the mother as early as possible. This is because immediately after parturition, the mammary glands start secreting colostrum, a form of milk that is rich in antibodies and improves the immune system of the baby. Every baby thus begins its journey as a zygote, which develops into a foetus over nine months.

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