1. conception, implantation and placentation

Question 1

Ovulation

Answer 1

• Ovulation is necessary for normal fertilization to occur.
• The ovum must leave the ovary and be carried into the fallopian tube.
• The unfertilized ovum is surrounded by its zona pellucida.
• This oocyte has completed its first meiotic division and carries its first polar body.

Question 2

Fertilization (conception)

Answer 2

• Fertilization typically occurs within 24 h’ after ovulation in the ampulla of the fallopian tube.
• The sperm penetrates the zona pellucida of the ovum.
• The male and female nuclear material combine to form a single cell (zygote).
• Fertilization signals the ovum to complete meiosis II and to discharge an additional polar body.

Question 3

Preimplantation

Answer 3

• The zygote starts to undergo cleavage (divide); at the 16 cells stage, it is called a morula.
• The morula divides to form a multicellular blastomere.
• The blastomere passes from the fallopian tube into the uterine cavity.
• The embryo develops into a blastocyst as it freely floats in the endometrial cavity after conception.
• Each cell of the preimplantation embryo is totipotent (can form all different types of cells in the embryo).

Question 4

implantation

Answer 4

• On day 5-6 after ovulation, the blastocyst adheres to the endometrium with the help of adhesion molecules on the secretory endometrial surface.
• After attachment, the endometrium proliferates around the blastocyst.

Question 5

Placentation

Answer 5

• During week 2, cells in the outer cell mass differentiate into trophoblasts.
• A trophoblastic shell forms the initial boundary between the embryo and the endometrium.
• The trophoblasts nearest the myometrium form the placental disk; the trophoblasts near the embryo form the chorionic membranes