Detailed exxplanations of FOETAL MEMBRANCES at different stages of embryonic development .

CBSE Class 12-science Answered

Detailed exxplanations of FOETAL MEMBRANCES at different stages of embryonic development .

Asked by pardeepkumar2281 | 13 May, 2018, 07:53: AM

Expert Answer

The growing embryo/foetus develops four membranes called extraembryonic or foetal membranes. These membranes include the chorion, amnion, allantois and yolk sac.

1. Amnion: The amnion is a membranous sac which surrounds and protects the embryo. At the beginning of the second week, the cells of the inner cell mass form into a two-layered disc of embryonic cells, and a space called amniotic cavity opens up between it and the trophoblast. Cells from the upper layer of the disc extend around the amniotic cavity, creating a membranous sac that forms into the amnion by the end of the second week. The amnion fills with amniotic fluid and eventually grows to surround the embryo.

2. Yolk sac: Opposite the amnion, cells in the lower layer of the embryonic disc extend into the blastocyst cavity and form a yolk sac. The yolk sac supplies nutrients absorbed from the lower embryonic disc that provides primitive blood circulation to the developing embryo for the second and third week of development.

3. Allantois: During third week, a finger-like projection of the yolk sac develops into the allantois, a primitive excretory duct of the embryo that becomes part of the urinary bladder. Together, the stalks of the yolk sac and allantois establish the outer structure of the umbilical cord.

4. Chorion: The last of the extra-embryonic membranes is the chorion, which is the one membrane that surrounds all others. It relates to the growth and development of the placenta.

Answered by Sivanand Patnaik | 13 May, 2018, 10:11: AM