The key difference between trophoblast and inner cell mass is that trophoblast is the outer cell layer of the blastocyst that nourishes the embryo and develops into a large part of the placenta while inner cell mass or embryoblast is the innermost cell mass from which the embryo arises.
A male sperm unites with an egg cell to form a zygote. This is the precognition for the formation of a new human being. Four days after fertilization, the young embryo has roughly 16 to 32 cells called blastomeres. Blastomeres separate into embryoblast (inner cell mass) and trophoblast. In this stage, it is called a blastocyst. Trophoblast is the outer cell layer of the blastocyst. Inner cell mass is the cells which give rise to the embryo.
CONTENTS
1. Overview and Key Difference
2. What is Trophoblast
3. What is Inner Cell Mass
4. Similarities Between Trophoblast and Inner Cell Mass
5. Side by Side Comparison – Trophoblast vs Inner Cell Mass in Tabular Form
6. Summary
What is Trophoblast?
Trophoblast is the outer layer of a blastocyst composed of a flat squamous epithelial layer of cells. It appears five days post fertilization in humans. Trophoblast cells are the first cells to differentiate from the fertilized egg. Trophoblast forms the outer sheet of inner cell mass and the blastocyst cavity. Trophoblasts cells provide nutrients to the embryo. It then develops into a large part of the placenta.
Figure 01: Trophoblast
Trophoblast cells form the first source for the placental membranes. Therefore, trophoplast is crucial for the correct function of the placenta. Trophoblast cells contribute to the initial adhesion to the uterine wall and subsequent implantation. Moreover, trophoblast differentiates into two layers: an outer syncytiotrophoblast and an inner cytotrophoblast.
What is Inner Cell Mass?
Inner cell mass is the innermost cell mass of the blastocyst, which is surrounded by the trophoblast. It is a cluster of cells attached to one wall of the outer trophoblast layer. The embryo arises from the inner cell mass. Hence, the inner cell mass is also known as embryoblast. Hence, inner cell mass is the source of true embryonic stem cells. These stem cells are the cells that are capable of forming all cell types within the embryo.
Figure 02: Inner Cell Mass
Inner cell mass differentiates into two distinct layers: the epiblast and hypoblast. Epiblast layer forms the entire embryo, and it undergoes gastrulation to produce three germ layers.
What are the Similarities Between Trophoblast and Inner Cell Mass?
- Trophoblast and inner cell mass are two structures of a blastocyst.
- Trophoblast and inner cell mass (embryoblast) form as a result of the separation of blastomeres.
- Trophoblast cell layer surrounds the inner cell mass.
- Trophoblast and inner cell mass have differentiated cell types.
What is the Difference Between Trophoblast and Inner Cell Mass?
Traphoblast and inner cell mass are two of the three structures of a blastocyst. The trophoblast is the outer cell layer while inner cell mass is the cluster of cells which forms the embryo. Thus, this is the key difference between trophoblast and inner cell mass. Trophoblast does not contribute to the formation of the embryo. It develops into a large part of the placenta and is crucial for the correct function of the placenta. Inner cell mass, on the other hand, will form the entire embryo consisting of embryonic stem cells which are capable of forming all cell types within the embryo.
Below infographic tabulates more differences between trophoblast and inner cell mass.
Summary – Trophoblast vs Inner Cell Mass
Blastocyst is a stage of the early development of the mammalian embryo. It consists of a blastocoel (fluid-filled cavity), inner cell mass and trophoblast (enveloping layer). Trophoblast is the outer cell layer of blastocyst. These cells directly do not contribute to the formation of the embryo. Instead, trophoblast provides nutrients to the embryo, and it becomes the precursor to the placenta. So trophoblast is crucial to establish a connection with the maternal uterus. The embryo arises from the inner cell mass. Inner cell mass is surrounded entirely by the trophoblast. So this is the difference between trophoblast and inner cell mass.
Reference:
1. “Blastocyst Development.” Embryology, Available here.
2. “Blastocyst.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available here.
Image Courtesy:
1. “Blastocyst English” By Seans Potato Business (derivative of the source cited above) – Blastocyst.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Stem cells diagram” By Mike Jones – (CC BY-SA 2.5) via Commons Wikimedia