Question

Name and describe very briefly, the stages in the development of human embryo.

Answer 1

1. Fertilisation: 
   1. The fertilised egg divides into a solid mass of cells called the Morula.
2. Morula to Blastocyst:
   1. The Morula transforms into a fluid-filled structure called the blastocyst.
   2. The blastocyst's outer layer, known as the trophoblast, has a nutritional purpose.
3. Implantation:
   1. The blastocyst, now a fluid-filled embryo, enters the uterus approximately 4-6 days after fertilisation.
   2. The trophoblast digests and embeds into the uterine endometrium, a process called implantation.
   3. Implantation initiates pregnancy and delivers oxygen and nutrients to the developing fetus.
4. Early embryonic development:
   1. During the first three weeks, the embryo is roughly the size of a large pea.
   2. By the 5th week, the embryo has developed the heart and blood vessels but lacks limbs.
5. Formation of the Foetus:
   1. During the 8th week of pregnancy, the foetus develops limbs similar to those of humans.
6. Role of the Placenta and Umbilical Cord:
   1. The placenta supplies materials through diffusion.
   2. The umbilical cord connects the placenta to the foetus.
7. Embryonic Membranes:
   1. The embryo is surrounded by three membranes: the amnion (which contains amniotic fluid), the chorion, and the allantois.
8. Gestation Period:
   1. The gestation period lasts around 280 days, from implantation to birth.
9. Childbirth:
   1. The baby is usually delivered head first due to strong uterine muscular contractions.
   2. The umbilical cord is cut, and the placenta is ejected after birth.