1. Week of Embyrogenesis: Pre-Embryo

by John McLachlan, PhD

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    Hello, and welcome to this lecture on the first week of human development, the pre-embryo stage. We'll be looking at the events from fertilization through to implantation. The first stage is on the fascinating journey of the human from egg to adult. The outcomes we’ll look at include looking at the early division stages, the cleavage stages as early parts of development and then we’ll look at implantation into the uterine wall, the uterus of the mother. We will touch briefly on one of the things that can go wrong, which is an ectopic pregnancy, and we’ll also look briefly at some reproductive technologies. So, let’s begin at the beginning. Here, we have a newly fertilized egg. Fertilization is covered in a separate lecture in this series. Now, this egg is large as human cells go, it is about 80 microns in diameter, about eight to ten times the size of a normal adult cell. When division takes place at these early stages, the cell is half in size at each division. So the two-cell stage is half the size of the egg itself, the four-cell stage is a quarter of the size, and so on until the cells reach something like the normal adult size. It’s important to understand that there’s no growth taking place at this time and the developing egg and the cells are surrounded by a protein coat called the zona pellucida. It’s an acellular, semi-rigid material surrounding the egg, and all of the divisions take place at these early stages inside the zona. At these stages, all the cells are still equivalent. So if I took a four-cell embryo and I divided up the cells into four individual cells, each one of them will be capable of giving rise to a full normal individual. They...

    About the Lecture

    The lecture 1. Week of Embyrogenesis: Pre-Embryo by John McLachlan, PhD is from the course Embryology: Advanced. It contains the following chapters:

    • Cell Division after Fertilisation
    • Hatching and Implantation
    • Ectopic Pregnancy
    • Assisted Reproductive Technology

    Author of lecture 1. Week of Embyrogenesis: Pre-Embryo

     John McLachlan, PhD

    John McLachlan, PhD

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