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Learn the BASIC CONCEPTS ABOUT THE THIRD WEEK OF GESTATION in an easy, fast and concise way.
#EMBRYOLOGY #MEDICINE #SUMMARY
⌚Time stamps:
Introduction 00:00
Review 2nd week of Gestation 0:45
Gastrulation - Trilaminar embryonic disc 1:14
Formation of the Notochord 4:43
Oropharyngeal, Cloacal and Allantoic Membrane 6:38
Embryonic Disc Growth 7:32
Chorionic Villi 7:57
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RESUME
The most relevant event during the third week of gestation is gastrulation, which begins with the appearance of the primitive streak, at whose cephalic end the primitive node is located. In the region of the node and the line, the cells of the epiblast move inwards (invagination) to form, the endoderm and the mesoderm. Cells that do not migrate down the line, but remain in the epiblast, form the ectoderm. Thus, the epiblast gives rise to the three germ layers of the embryo, ectoderm, mesoderm and endoderm, and these layers form all tissues and organs.
The prenotochord cells that invaginate in the primitive fossa become
move until they reach the prechord plate. They are interspersed in the endoderm to integrate the notochordal plate. As development progresses, the plate becomes
it detaches from the endoderm and forms a solid cord, the notochord. Is
establishes an axis in the midline, which will serve as the basis for the axial skeleton. The cranial and caudal ends of the embryo are determined before
let the primitive line be formed.
The cells of the epiblast that travel through the node and the line are predetermined according to their position to become specific types of mesoderm and endoderm. Thus, it is possible to construct a destination map of the epiblast in which this pattern is observed.
By the end of the third week, three germ layers have established
ectoderm, mesoderm and endoderm, in the head region, and the process continues to form these germ layers in more caudal regions of the embryo until the end of the fourth week. Tissue and organ differentiation has begun, proceeding cephalocaudal as gastrulation continues. Meanwhile, the trophoblast evolves rapidly. The primary villi acquire a mesenchymal center in which small capillaries arise. When these capillaries of the villi come into contact with those of the chorionic plate and the fixation pedicle, the villous system is ready to provide the embryo with nutrients and oxygen.