1. FIRST WEEK OF PREGNANCY Segmentation Dr. Sherif Fahmy

2. START OF CLEAVAGE Fertilization leads to formation of a zygote which is a fertilized ovum surrounded with zona pellucida. Fertilization leads to formation of a zygote which is a fertilized ovum surrounded with zona pellucida. Zygote divides by mitotic division to form 2-cell stage- ---- 4-cell stage -------- 8-cell stage ------- 16-cell stage --------- 32-cell stage ------ 64-cell stage (morula). Zygote divides by mitotic division to form 2-cell stage- ---- 4-cell stage -------- 8-cell stage ------- 16-cell stage --------- 32-cell stage ------ 64-cell stage (morula). Cells of morula are called blastomere. Cells of morula are called blastomere. Formation of morula takes 3 days through which it is transmitted through the uterine tube. Formation of morula takes 3 days through which it is transmitted through the uterine tube. Zona pellucida prevents adhesion of zygote to uterine tube and prevents separation of cells. Zona pellucida prevents adhesion of zygote to uterine tube and prevents separation of cells. Dr. Sherif Fahmy

3. Formation of Morula By the end of 4 th day, zona pellucida ruptures due to increase in number of blastomeres. By the end of 4 th day, zona pellucida ruptures due to increase in number of blastomeres. The blastomeres that remain after rupture of zona is called morula. The blastomeres that remain after rupture of zona is called morula. Fluid enters between cells and forms acavity (blastocele) which separates cells into outer cell mass (trophoblast) and inner cell mass (embryoblast). This stage is called blastocyst which is formed at the 6 th day. Fluid enters between cells and forms acavity (blastocele) which separates cells into outer cell mass (trophoblast) and inner cell mass (embryoblast). This stage is called blastocyst which is formed at the 6 th day. Embryoblast forms fetus while trophoblast form placenta, amniotic cavity and umbilical cord. Embryoblast forms fetus while trophoblast form placenta, amniotic cavity and umbilical cord. Dr. Sherif Fahmy

12. BLASTOCYST It is formed at the 6 th day from morula which a cavity develop a cavity (blastocele). It is formed at the 6 th day from morula which a cavity develop a cavity (blastocele). Cells of blastocyts separates into outer cell mass and inner cell mass. Cells of blastocyts separates into outer cell mass and inner cell mass. Outer cell mass (trophoblast) is responsible for absorption of nutritive material which is uterine fluid (uterine milk). Outer cell mass (trophoblast) is responsible for absorption of nutritive material which is uterine fluid (uterine milk). Inner cell mass (embryoblast) will form the embryo Inner cell mass (embryoblast) will form the embryo Dr. Sherif Fahmy