Which layer is the combination of endoderm, mesoderm and ectoderm that gives rise to the tissues of the embryo?

Question

BlackTom AI · Accepted Answer

The trilaminar embryonic disc is the structure composed of ectoderm, mesoderm and endoderm that gives rise to the tissues of the embryo, so the correct choice is the embryonic disc.

1) Relevant knowledge points and concepts
- Inner cell mass of the blastocyst differentiates into a bilaminar disc (epiblast + hypoblast).
- Gastrulation (around week 3 in humans) transforms the bilaminar disc into a trilaminar embryonic disc containing three primary germ layers: ectoderm, mesoderm, and endoderm.
- These three germ layers are the source of all embryonic tissues and organs: ectoderm → nervous system and skin, mesoderm → muscle, bone, blood, and connective tissue, endoderm → gut lining and associated organs.
- Other listed structures (trophoblast, blastocoele, allantois) are extraembryonic or structural components, not the primary source of embryonic tissues.

2) Step-by-step reasoning
- The blastocyst contains a fluid cavity (blastocoele), an outer trophoblast, and an inner cell mass.
- The inner cell mass becomes the bilaminar embryonic disc (epiblast and hypoblast).
- Gastrulation produces the third layer (mesoderm) from the epiblast, creating the trilaminar embryonic disc (ectoderm, mesoderm, endoderm).
- Because the trilaminar disc is explicitly the combination of those three layers, it is the structure that gives rise to the embryo’s tissues.

3) Calculations
- Not applicable (developmental sequence is conceptual rather than numerical).

4) Why the correct answer is correct
- "Embryonic disc" refers to the developing embryo’s germ-layer-bearing structure; by definition it contains the three germ layers responsible for forming embryonic tissues.

5) Why other options are incorrect
- a. Trophoblast: outer cell layer that contributes to placenta and implantation, not embryonic tissues.
- b. Blastocoele: fluid-filled cavity inside blastocyst, not a tissue-forming layer.
- d. Allantois: extraembryonic membrane involved in waste and blood vessel formation, not the primary source of embryonic tissues.

6) Conclusion
This reasoning confirms that option c. Embryonic disc is the correct answer.

Which layer is the combination of endoderm, mesoderm and ectoderm that gives rise to the tissues of the embryo?Single choice

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