Week 3 of embryonic development | Gastrulation | Neural induction

Summary

In this lecture on embryology, the third week of embryonic development is discussed, with a focus on key events such as gastrulation, the formation of germ layers, and the development of the notochord. By day 16, the primitive streak forms, marking the body axis and initiating cell movements like ingression, which lead to the formation of the ectoderm, mesoderm, and endoderm. The notochordal process begins by day 17, triggering neural induction and the formation of the neural tube. This process is crucial for the formation of various structures, including the brain, skin, kidneys, and GI tract.

Takeaways

• 😀 The third week of embryonic development is crucial, marked by major events like gastrulation and notochord formation.
• 😀 At the end of week two, the blastocyst fully embeds into the endometrium, and the chorionic cavity forms.
• 😀 Gastrulation, which starts around day 16, is a key process where the three germ layers (ectoderm, mesoderm, and endoderm) are formed.
• 😀 The primitive streak, which forms along the midline of the embryo, marks the beginning of gastrulation and defines the major body axis.
• 😀 The primitive groove forms at the cranial end of the primitive streak, marking the first significant step in body axis formation.
• 😀 The process of ingression involves epiblast cells moving through the primitive streak to form new germ layers.
• 😀 The epiblast cells give rise to ectoderm, mesoderm, and endoderm, which later develop into various body structures.
• 😀 At day 16, the ectoderm, mesoderm, and endoderm are fully formed, setting the foundation for further development.
• 😀 The notochord, which forms at the cranial end of the primitive streak, is essential for neural tube induction and spinal cord development.
• 😀 By days 19 to 21, the neural tube forms as the ectoderm folds, a process called neurulation, marking the early stages of CNS formation.

Q & A

What is the main focus of the video?

The video focuses on the third week of embryonic development, specifically the events that occur during this week, such as gastrulation and the formation of the three germ layers: ectoderm, mesoderm, and endoderm.

What happens at the end of week two in embryonic development?

At the end of week two, the blastocyst has completely embedded into the endometrium, and the chorionic cavity forms. The bilaminar embryonic disc is suspended in this cavity, connected by the primitive streak, which will eventually become the umbilical cord.

What is gastrulation, and why is it important?

Gastrulation is the process during the third week of embryonic development where the bilaminar embryonic disc undergoes complex movements to form the three primary germ layers—ectoderm, mesoderm, and endoderm—which will later differentiate into various tissues and organs.

What are some of the key morphogenetic movements involved in gastrulation?

Key morphogenetic movements during gastrulation include invagination, involution, ingression, delamination, and epiboly. These movements help the cells of the embryo move into new positions and become different cell types.

How does the primitive streak contribute to gastrulation?

The formation of the primitive streak is the first event in gastrulation. It defines the major body axis, with the cranial (head) and caudal (tail) ends, and marks the beginning of coordinated cell movement that forms the three germ layers.

What is the role of the primitive node in embryonic development?

The primitive node, located at the cranial end of the primitive streak, has a depression known as the primitive pit. This structure is important for cell migration during gastrulation, and it also gives rise to the oropharyngeal membrane, which later forms the mouth.

What happens during the process of ingression?

Ingression is the movement of cells through the primitive streak. Cells move inward, then away from the streak, and differentiate into various tissue types, such as mesoderm and endoderm.

What is the significance of the notochordal process?

The notochordal process, which starts forming around day 17, is crucial for the development of the vertebral column and induces the formation of the neural tube, which will eventually give rise to the central nervous system.

What is neural tube induction, and when does it occur?

Neural tube induction is the process by which the ectoderm, under the influence of signaling molecules from the notochord, folds to form the neural tube. This occurs between days 19 to 21 of embryonic development.

What structures do the three germ layers give rise to?

The ectoderm gives rise to the central nervous system, skin, and adrenal medulla. The mesoderm forms structures like the kidneys, bones, heart, and spleen. The endoderm develops into the gastrointestinal tract, endocrine system, bladder, and urethra.