Which human organ system is the first to becomg visibly differentiated during development?

Question

As I already know that the endoderm is the middle layer, which overtime develops into our internal organs. I still don't really understand how to answer this question. Any advice would be greatly appreciated.

THANKS!

Answer 1

epodermis skin

Answer 2

the brain

Answer 3

("Development in humans last about 280 days or 40 +/- 2 weeks from fertilization until birth.  ... a single-celled zygote to a baby occurs.  Fertilization ... occurs in the fallopian tube.  The zygote divides rapidly by cleavage as it travels towards the uterus.  It enters the uterus 3 days after fertilization. .... All the organ systems of a human embryo begin to develop withing 60 days (eight and a half weeks) following fertilization ....  The heart begins to beat after 4 weeks. By eight weeks the eyes, ears, nose, mouth and fingers and toes are easily recognizable ....")

As I recall, the heart is the first organ system to more fully differentiate and become visibly observable as a functioning organ.

See: Cornell Institute for Biology Teachers

http://cibt.bio.cornell.edu/labs/dl/FDEV...