Allantois 〈RECENT ✪〉

myesr.org/poster/esr/ecr2020/C-10164/background">urachal cysts or other developmental remnants?

: It is present in all amniotes, including reptiles, birds, and mammals. allantois

The is a critical extra-embryonic membrane found in the embryos of reptiles, birds, and mammals that primarily functions in waste storage and gas exchange . In egg-laying species, it acts as a repository for nitrogenous waste and works with the chorion to facilitate respiration, while in most mammals, it evolves to form the structure of the umbilical cord. 1. Evolutionary Significance and Structure In egg-laying species, it acts as a repository

While its fundamental purpose is life support, the specific role of the allantois varies significantly between species: This membrane serves as a "lung," allowing oxygen

: In these egg-layers, the allantois expands until it fuses with the chorion to form the chorioallantoic membrane . This membrane serves as a "lung," allowing oxygen to enter the egg and carbon dioxide to leave. It also acts as a storage tank for uric acid, a non-toxic form of nitrogenous waste.

: The allantois and yolk sac are incorporated into the connecting stalk to form the umbilical cord.

As human gestation progresses, the allantois undergoes a transformation: