K12 Week 5 to 8

From Embryology

Week 5 to 8

width=400px|height=415px|controller=true|autoplay=true</qt> Week 8 Embryo

This movie shows the internal organs (gastrointestinal tract and lungs).

(red) lungs

(purple) stomach

See the size and position of these organs at this early stage of development.

See also that some of the gastrointestinal tract (intestines) lie outside the embryo at this time in development.

Adult gastrointestinal tract cartoon.jpg

Adult gastrointestinal tract cartoon

In the fifth to eigth (5-8) week of embryo development, organs begin to form within the embryo. This period covers approximately the last stages of major embryonic development growth (Carnegie stages), after this time the embryo is described as a fetus.

Start by comparing at the outside (external) changes in what the embryo looks like from week 5 to week 8 in the pictures below. What new things can you see over this period?

Even though from the outside the embryo now looks very developed, if we were to look inside the embryo's head for a brain, we would find only a very thin layer of cells surrounding a large fluid-filled space. (almost like a water-filled balloon).

Then have a look at living embryos in the ultrasound movies below. The first 2 movies are at 7 weeks (the first a single embryo, the second twins). The next movie is one week later (week 8) where the limb buds and spine can now be clearly seen. At this early stage ultrasound shows the beating heart is the most obvious feature within the embryo. Ther is also another page covering this period looking at development of the arms and legs.

Cite this page: Hill, M.A. (2021, June 19) Embryology K12 Week 5 to 8. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/K12_Week_5_to_8

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G