K12 Week 3

From Embryology

Week 3

In the third week of development the blastocyst has now burrowed into the wall of the uterus and cells on the outside are beginning to form early parts of the placenta.

This movie shows folding of the embryonic disc beginning week 3 of development.


(blue) The embryo has been cut in the middle from head to tail to show the growth and folding.

(yellow) The gastrointestinal tract.

(red right) The connecting stalk that will form the future placental cord.

(red left with white "8" shaped cavity) The early heart.

A week 3 Human Embryo

The clump of cells inside the blastocyst has also begun to change and now looks like 2 discs of cells. It looks like 2 dinner plates stacked on top of each other. The picture shows looks at this stack from the top. Cell from the top plate move down to form a new layer.

The embryo now looks like stacked 3 dinner plates.

We use stages as a way of measuring changes in the embryo. Stages are like different years at school: each year something new will occur, each stage something new will happen. Stages are also a way of comparing changes that occur in different animals.


K12 Links: Start Here | Week 1 | Week 2 | Week 3 | Week 4 | Week 5 to 8 | Arms and Legs | Heart | Fetus | Brain Growth | Eyes and Ears | Animal Development Times | Humans and Animal Embryology | Comparative Embryology | Thalidomide



Cite this page: Hill, M.A. (2019, January 19) Embryology K12 Week 3. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/K12_Week_3

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G