Question

Describe, in detail, the events that will occur from the time that the zygote formed until that embryo achieves maternal recognition of pregnancy.

Answer 1

Zygote is formed by the fusion of male and female gamete. The zygote develops into embryo.The zygote starts to divide and multiply. As it travels toward the uterus it divides to become a blastocyst, which will burrow into the uterine wall.

2. The Zygote Becomes an Embryo: This is the Development Prior to and During Implantation

The initially formed zygote , takes about five days to reach the uterus from the uterine tube. As it moves, the zygote divides and develops into a blastocyst, with an inner mass of cells and a protective outer ring. The blastocyst attaches to the wall of the uterus and gradually implants itself into the uterine lining. During implantation, its cells differentiate further. At day 15 after conception, the cells that will form the embryo become an embryonic disc. Other cells begin to form support structures. The yolk sac, on one side of the disc, will become part of the digestive tract. On the other side, the amnion fills with fluid and will surround the embryo as it develops. Other cell groups initiate the placenta and umbilical cord, which will bring in nutrients and eliminate waste.

3. In 8 Weeks, the Embryo Develops; By the End of Week 10 It Becomes a Featus

Fifteen days after conception marks the beginning of the embryonic period. The embryo contains a flat embryonic disc that now differentiates into three layers: the endoderm, the mesoderm, and the ectoderm. All organs of the human body derive from these three tissues. They begin to curve and fold and to form an oblong body. By week 4, the embryo has a distinct head and tail and a beating heart. Over the next six weeks, limbs, eyes, brain regions, and vertebrae form. Primitive versions of all body systems appear. By the end of week 10, the embryo is a fetus.

• Embryo’s heart is formed after one month of pregnancy. The heart-beat of the fetus can be heard at this stage; with the help of stethoscope. This is the first sign of the growing fetus.
• By the end of the second month, the fetus develops limbs and digits.
• By the end of 12 weeks (first trimester), most of the major organ systems are formed. Limbs and external genital organs are well developed at this stage.
• By the end of the 24 weeks (second trimester), the body is covered with fine hair, eyelids separate, and eyelashes are formed.
• By the end of nine months, the foetus is fully developed and is ready for delivery.

4. Fetal Development Ends with Labor, a Three-Stage Process

From week 10 of pregnancy, the fetus grows inside the uterus, fueled by nutrient-rich blood supplied by the umbilical cord. The placenta provides oxygen and nutrients to the fetus and removes waste products from the fetus’ blood. Bones, muscles, skin, and connective tissues form. Body systems develop. Limbs and facial features take shape. Around week 36 the process of labor begins. In the first stage, dilation, hormones stimulate downward contractions of the uterine walls. The contractions push the head of the fetus against the cervix at the lower end of the uterus. The cervix dilates. In the second stage, expulsion, powerful contractions push the head and the rest of the body through the dilated cervix, . The baby is born. Further contractions expel the placenta to complete the placental stage.