Learning aims
- Describing the development of the embryo from the first cells to the blastocyst
- Knowing the important stages of the preimplantation phase
- Describing the importance of these stages
- Knowing the duration of the preimplantation phase
What you should already know
- The processes during fertilization that lead to the formation of the zygote
Delving deeper
- How does the early embryo get to the uterus; how does it find its way?
- From what does the embryo nourish itself until its implantation?
- How is the blastocyst formed?
Introduction
Following a successful fertilization the preimplantation period that lasts for around 6 days ensues.
While the fertilized oocyte wanders from the ampulla through the fallopian tube into the uterine cavity, an implantation-ready blastocyst develops through cell divisions. At the end of the sixth day after fertilization the blastocyst embeds itself in the endometrium.
- Pellucid zone
- Blastomere (cleavage cell)
- Polar bodies
- 4
- Inner collection of cells
(embryoblast) - 5
- Blastocyst cavity
A two-cell embryo has been created through the division of the zygote. Picture made roughly 24 hours after the in-vitro fertilization
Fig. 2This form of the embryo is called a blastocyst because the cells enclose a fluid-filled cavity on the inside. On the fifth day after fertilization.
© Dr. A. Senn et al, CHUV Lausanne
- 1
- Ovary
- 2
- Fallopian tube
- 3
- Endometrium
- 4
- Myometrium
- 5
- Uterine cavity
- A
- Impregnated oocyte
- B
- Two-cell stage
- C
- Blastocyst
The green line marks the path the embryo travels in the first six days until it reaches the implantation location in the uterine cavity. The images under A, B and C represent three snapshots of the evolution of the oocyte from a fertilized state (A), through a two cell stadium (B) to a blastocyst (C)