87) Explanation • As the amniotic cavity enlarges, it obli | Anatomy embryology histology videos & books

87) Explanation




• As the amniotic cavity enlarges, it obliterates the chorionic cavity and covers the connecting stalk and gets reflected at the region of primitive umbilical ring (amino-ectodermal junction).

• The primitive umbilical region gradually gets crowded and contains:
(i) connecting stalk having allantois, umbilical vessels (two arteries and one vein),
(ii) yolk stalk (vitelline duct) along with vitelline vessels, and
(iii) the canal connecting the intraembryonic and extraembryonic cavities.

• All these structures finally give rise to primitive umbilical cord. A part of the yolk sac which lies in the chorionic cavity later shrinks and gets obliterated.
• Initially when the abdominal cavity is too small, and the loops of intestine grow very fast, some of them get pushed into the extraembryonic space in the umbilical cord. This is called physiological umbilical hernia.
• By the end of the third month, the abdominal cavity enlarges and the loop of intestine returns into the abdomen and the extraembryonic cavity of umbilical cord gets obliterated.
• The structures of the umbilical cord, i.e., vitelline duct, vitelline vessels and allantois also get obliterated and are converted into Wharton’s jelly. The only structures which remain functional in Wharton’s jelly are the umbilical vessels.