Question

A newborn is presented to you with a huge mass located at the anal region, which you recognize as a sacrococcygeal teratoma. You know that is the persistence of the primitive streak, formed from the A. hypoblast. B. prochordal plate. C. epiblast.

Short answer

C. epiblast

Step-by-step solution

Understanding the Primitive Streak

The primitive streak is a structure that forms during the early stages of embryonic development. It is crucial in the process of gastrulation, where the three germ layers (ectoderm, mesoderm, and endoderm) are formed.

Identifying the Derivation of the Primitive Streak

The primitive streak originates from the epiblast, which is one of the two layers of cells in the bilaminar disk stage of the embryo. The epiblast cells migrate to form the primitive streak.

Analyzing the Options

Given the options: A. hypoblast, B. prochordal plate, C. epiblast, only the epiblast is involved in the formation of the primitive streak.

Choosing the Correct Answer

The correct answer is C. epiblast, as the primitive streak is formed from the epiblast cells.

Key concepts

epiblast

The epiblast is a layer of cells that plays a pivotal role in early embryonic development. It is one of the two layers in the bilaminar germ disk, the other being the hypoblast. The epiblast gives rise to all three primary germ layers: ectoderm, mesoderm, and endoderm through a process called gastrulation.
The epiblast's significance lies in its contribution to the primitive streak. This structure appears as a thickened area on the surface of the embryonic disk and acts as a central point from which cells migrate to form different tissue layers.
Without the epiblast, proper embryonic development would be impossible because it is fundamental to forming the body plan of the embryo.

gastrulation

Gastrulation is a crucial phase in embryonic development where the single-layered blastula reorganizes into a multi-layered structure called the gastrula.
During this process, cells from the epiblast layer move inward to form the three primary germ layers:
- Ectoderm: This layer forms the skin, nervous system, and other external tissues.
- Mesoderm: This layer gives rise to muscles, bones, and the circulatory system.
- Endoderm: This layer forms the internal organs such as the liver and intestines.
The formation of the primitive streak is an essential event in gastrulation. It sets the stage for the migration and differentiation of cells into their respective germ layers.
Gastrulation ensures that cells are properly positioned to form the various tissues and organs of the body, making it foundational for embryonic development.

embryonic development

Embryonic development refers to the stages an embryo undergoes to form a fully developed organism. This complex process involves multiple phases and key structures starting right after fertilization.

Key stages in embryonic development include:
1. **Fertilization**: The union of sperm and egg cells to form a zygote.
2. **Cleavage**: Rapid cell division without growth, resulting in a multi-cellular embryo.
3. **Blastulation**: Formation of the blastula, a hollow ball of cells.
4. **Gastrulation**: As previously mentioned, this crucial phase involves the formation of the three germ layers from the epiblast cells, significantly driven by the primitive streak.
5. **Organogenesis**: Development of organs and structures from the germ layers.
Throughout these stages, the proper formation and function of structures like the primitive streak are vital for the successful development of the embryo.
It is through these coordinated events that a single-celled zygote transforms into a complex, multi-cellular organism.