Fertilization (CH. 26)

What happens when the human sperm and oocyte meet?

Acrosomal enzymes from multiple sperm create gaps in the corona radiata.
One sperm fuses with the oocyte membrane, causing oocyte activation and completion of meiosis II.
Female and male pronuclei form.
The pronuclei fuse (amphimixis), forming a zygote with 46 chromosomes.
Cleavage begins ~30 hours after fertilization, producing two blastomeres.

What is a blastomere?

One of the smaller daughter cells produced by the cleavage divisions of the zygote. The first cleavage produces two blastomeres about 30 hours after fertilization.

What is a morula?

A solid ball of cells (blastomeres) formed about 3 days after fertilization, during the pre-embryo stage

what is blastocyst?

A hollow ball of cells formed about 5 days after fertilization. It has an internal cavity (blastocoele), an outer trophoblast layer, and an inner cell mass that will form the embryo

What are the inner cell mass cells?

Forms embryo “turns into human”

What happens to the inner cell mass and syncytial trophoblast during implantation?

 • Chorion – outer covering
 • Syncytial trophoblast – invades the endometrium and secretes enzymes to erode maternal tissue.
– The inner cell mass begins forming embryonic tissues.
Implantation completes around day 10.

Define Yolk sac

makes RBCs 

Define Amnion

just a sac helps the embryo to grow 

Allantois

forms the base of the urinary bladder

Define chorion

comes from trophoblast …