Gastrulation - Anatomy & Physiology

BACK TO DEVELOPMENTAL BIOLOGY

Introduction

Gastrulation is the process of forming the three germ layers; ectoderm; mesoderm; and endoderm. It is achieved through a series of highly coordinated series of cell movements. Cells that will form the endodermal and mesodermal organs are brought inside the embryo, whilst cells that will form ectoderm move to spread out over the outside of the embryo.

• Ectoderm - outside layer
• Mesoderm - middle layer
• Endoderm - inner layer

Germ Layer	Derivatives
Ectoderm	Neural Ectoderm - PNS & CNS Non Neural Ectoderm - Epidermis of skin
Mesoderm	Axial Mesoderm - Notochord, which is mostly degenerated Paraxial Mesoderm - Somites, which form axial skeleton and dermal muscle of the body Intermediate Mesoderm - Parts of reproductive system and kidneys Lateral Plate Mesoderm - Heart, limbs, tissue around gut
Ectoderm	Parynx, lungs, liver, lining of gut

Mechanism of Gastrulation

• When the embryo is in it's blastula stage it has two cell layers; the epiblast and hypoblast.
  • The epiblast is columnar whilst the hypoblast is cubiodal - each is a single cell thick.
• The epiblast gives rise to all three cell layers; the hypoblast makes no contribution.
• The endoderm and mesoderm develop by proliferation and migration of cells of the epiblast.
  • What remains of the epiblast forms the ectoderm.
• Gastrulation occurs at three embryonic sites:

Primitive Streak

Node

Tail Bud