Embryonic development - Week 3

210

0

HWC

By: HWC

Date Uploaded: 09/28/2019

Tags: Fertilization   human body  

Week 3 (gastrulation) • Three primary germ layers are formed which provide cells for organ formation in the following months. • These germ cell layers are formed by a process known as gastrulation, which involves rearranging epiblast cells. • As cells from the epiblast migrate, a faint groove called the primitive streak forms on the surface of the embryonic disc. • With the formation of the primitive streak, it is possible to recognize the head and tail ends of the embryo. • Some epiblast cells migrate, differentiate, and then replace the hypoblast to form the endoderm germ layer. • Other epiblast cells migrate and differentiate to form a new layer, between the epiblast and hypoblast, identified as the mesoderm germ layer. • The remaining epiblast cells become the ectoderm germ. • The trilaminar embryonic disc has three germ layers: • The ectoderm gives rise to all nervous tissue and the epithelium of the skin. • The mesoderm gives rise to blood, muscle, bone, and connective tissue. • The endoderm forms into the epithelium of the gastrointestinal tract, the respiratory system and many organs. Week 3 (neural tube formation) • Further differentiation of mesodermal cells begins the formation of the notochord. • The notochord is important in starting (or inducing) the specialization of other cells, including those directly above them called the neural plate. • Epiblastic cells in the neural plate are induced to begin to mound up and fold into a groove. • The neural groove continues to fold. • Adjacent notochord mesodermal cells are induced to form somites, the eventual source of cells to form skeletal and other connective tissues, and muscle tissue. • The neural tube arises and its cells eventually develop to form the brain, spinal cord, and other parts of the nervous system. Week 3 (heart and vessel formation) • Mesodermal cells from the primitive streak rearrange to form blood vessels in the embryo, and a primitive heart begins to form. • The chorionic villi projecting into the endometrium forms an exchange area called the intervillous space. • Maternal and fetal blood vessels remain separate, so maternal and fetal blood don't normally mix. • However, oxygen, antibodies, nutrients, and waste products are all exchanged via the intervillous spaces.

Share

Embed

Copy and paste this code into your website or blog.

Add To

You must login to add videos to your playlists.

Comments

0 Comments total

to post comments.

No comments have been posted for this video yet.