Difference Between Epiblast and Hypoblast

The key difference between epiblast and hypoblast is that epiblast is one of the two layers of the embryonic disc that forms three primary germ layers (ectoderm, definitive endoderm, and mesoderm), amnionic ectoderm, and extraembryonic mesoderm, while hypoblast is the second layer of the embryonic disc that forms the yolk sac.

Fertilization is the process of uniting an egg cell with a sperm, forming a diploid zygote. The zygote then eventually develops into an embryo via cell divisions and cell differentiation. After a few days of fertilization, the zygote undergoes several cell cleavages and forms the morula stage, which is the 16 cell stage. It has two cell masses called inner cell mass (embryoblast) and outer cell mass (trophoblast). Furthermore, inner cell mass forms the two cell layers – epiblast and hypoblast – which will form the embryo proper and yolk sac, respectively. The outer cell mass will be a part of the placenta.

CONTENTS

1. Overview and Key Difference
2. What is Epiblast 
3. What is Hypoblast
4. Similarities Between Epiblast and Hypoblast
5. Side by Side Comparison – Epiblast vs Hypoblast in Tabular Form
6. Summary

What is Epiblast?

Epiblast or primitive ectoderm is one of the two cell layers of the embryonic disc. It lies above the hypoblast. Moreover, the cells of epiblast are columnar in shape.

The epiblast gives rise to the three primary germ layers (ectoderm, definitive endoderm, and mesoderm), amnionic ectoderm and extraembryonic mesoderm. During gastrulation, the formation of a primitive streak takes place in the epiblast. It determines the midline of the body and separates the left and right sides.

What is Hypoblast?

Hypoblast is the inner or bottom layer that arises from the inner cell mass. Primitive endoderm is a synonym for hypoblast. The cells of the hypoblast are cuboidal cells.

Hypoblast lies on the top of the epiblast cells. It forms the yolk sac. Further, its cells do not contribute to the embryo. But, it influences the orientation of the embryonic axis.

What are the Similarities Between Epiblast and Hypoblast?

• Epiblast and hypoblast are two components that make the embryonic disc.
• The inner cell mass divides into layers to form epiblast and hypoblast. Thus, epiblast and hypoblast arise from the inner cell mass.
• Moreover, hypoblast cells lie on the top of the epiblast cells.
• Formation of both layers occurs prior to implantation and gastrulation.

What is the Difference Between Epiblast and Hypoblast?

Epiblast is one of the two layers of the embryonic disc that forms three primary germ layers, while hypoblast is the second layer of the embryonic disc that forms the yolk sac. So, this is the key difference between epiblast and hypoblast. Furthermore, epiblast contributes to the embryo, while hypoblast does not contribute to the embryo. Moreover, epiblast cells are columnar cells, while hypoblast cells are cuboidal cells. Therefore, this is also a significant difference between epiblast and hypoblast.

Summary – Epiblast vs Hypoblast

Epiblast and hypoblast arise from the inner cell mass during early embryonic development. Epiblast forms three germ layers and the amnion while hypoblast forms the yolk sac. Moreover, epiblast cells are columnar cells, while hypoblast cells are cuboidal cells. Furthermore, epiblast is the upper layer, while hypoblast is the lower layer. So, this summarizes the difference between epiblast and hypoblast.

Reference:

1. “Hypoblast.” Hypoblast – an Overview | ScienceDirect Topics, Available here.
2. “Human Embryogenesis.” Khan Academy, Khan Academy, Available here.

Image Courtesy:

1. “Human Embryo Day9” By Panzer VI-II – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Image from page 495 of “Elementary text-book of zoology [electronic resource]” (1901)” By Internet Archive Book Images (No known copyright restrictions) via Flickr