Learning aims, what you should already know, introduction, delving deeper

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?

Key concepts

Concepts that are important in the preimplantation phase..

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.

media/module5/e0a_zweizell.jpg — **Fig. 1 -** Two cell stage

media/module5/e0b_blastozyste.jpg — **Fig. 2 -** Blastocyst

Legend

Fig. 1

A two-cell embryo has been created through the division of the zygote. Picture made roughly 24 hours after the in-vitro fertilization

Fig. 2

This 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

media/module5/e0c_wanderung01.gif — **Fig. 3 -** Fallopian tube

Legend

Fig. 3

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)