FIRST WEEK OF PREGNANCY

Segmentation

Dr. Sherif Fahmy

START OF CLEAVAGE 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).

Cells of morula are called blastomere. 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.Dr. Sherif Fahmy

Formation of Morula By the end of 4th day, zona pellucida

ruptures due to increase in number of blastomeres.

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 6th day.

Embryoblast forms fetus while trophoblast form placenta, amniotic cavity and umbilical cord.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

BLASTOCYST

It is formed at the 6th day from morula which a cavity develop a cavity (blastocele).

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).

Inner cell mass (embryoblast) will form the embryo

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy