2011 Lab 3

Trilaminar Embryo to Early Embryo

Introduction

The first laboratories covered gametogenesis, fertilization, implantation and early events of embryonic development. The third week (Clinical week 5 LMP) is the begining of the embryonic period which continues through to week eight.

This laboratory will look at the third to fourth week of human development (stage 7 onward). We will be using a range of online materials and resources to explore these topics. The laboratory will also allow time for work on the group online project. Note that during this time the conceptus cells not contributing to the embryo are contributing to placental membranes and the early placenta.

The best way of beginning to understand the sequence is by considering the "stages" of development in relation to age (in days or weeks). Stages are based on the external and/or internal morphological development of the vertebrate embryo, and are not directly dependent on either age or size. Historically, the human embryonic period proper is divided into 23 Carnegie stages and criteria beyond morphological features include age in days, number of somites present, and embryonic length have sometimes been included in the stage descriptions. These stages are also shown in the movie Carnegie stage human growth through embryonic period.

Objectives

1. Understand the conceptus changes during week 3 and 4.
2. Understand the process of gastrulation and the trilaminar embryo.
3. Understand the development of the germ layers: mesoderm and ectoderm.
4. Identify abnormalities associated with this period of development.