3rd -4th Week Flashcards
What are the key events in the third week of pregnancy?
Gastrulation, notochord formation, formation of cloacal and buccopharyngeal membranes, neurulation, and allantois formation with three types of chorionic villi.
What is the definition of gastrulation?
The process by which the epiblast forms the three intra-embryonic germ layers (endoderm, mesoderm, ectoderm).
When does gastrulation occur?
During the third week of development.
What is the primitive streak?
A narrow groove on the epiblast’s surface in the midline near the caudal end of the embryo.
What is the primitive node?
A rounded elevation at the cephalic end of the primitive streak with a small pit called the primitive pit.
What happens during the migration phase of gastrulation?
Epiblast cells migrate toward the primitive streak, become flask-shaped, detach, and contribute to forming germ layers.
What do the first invaginated cells during gastrulation form?
The intra-embryonic endoderm.
What do the next invaginated cells form after the endoderm?
The intra-embryonic mesoderm.
What does the remaining epiblast form?
The ectoderm.
How does the shape of the embryonic disc change?
From rounded to oval to pear-shaped with a broad cranial end and narrow caudal end.
What are the two layers of the bilaminar embryonic disc?
Epiblast (dorsal layer of columnar cells) and hypoblast (ventral layer of cuboidal cells).
What are the three layers of the trilaminar embryonic disc?
Ectoderm, mesoderm, and endoderm (except at the buccopharyngeal and cloacal membranes, which lack mesoderm).
What is the notochord?
A solid cord in the axis of the embryonic disc between the ectoderm and endoderm, around which the vertebral column forms.
What is the notochordal process?
A tube-like structure formed by cells invaginated through the primitive pit moving cephalically to the future buccopharyngeal membrane.
What is the notochordal canal?
A canal formed by the extension of the primitive pit through the notochordal process.
What is the notochordal plate?
The roof of the notochordal canal that fuses with the endoderm, then folds to form the definitive notochord.
What is the function of the neuro-enteric canal?
A temporary communication between the amniotic cavity and yolk sac that closes as the endoderm regenerates.
What induces the formation of the neural plate?
The notochord.