Allantois

: In humans, the allantois is largely vestigial as a sac but remains vital as a structural precursor. Its blood vessels become the umbilical arteries and veins , connecting the fetus to the placenta for nutrient and gas exchange. 3. Developmental Fate in Humans

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

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

: It is derived from the splanchnopleure, which consists of endoderm and splanchnic mesoderm. 2. Functional Diversity Across Species

: The intra-embryonic portion of the allantois contributes to the development of the urinary bladder. After birth, it regresses into a fibrous cord known as the urachus or the median umbilical ligament. Summary of Key Roles Species Context Excretion Stores uric acid and nitrogenous waste. Birds and Reptiles Respiration Facilitates gas exchange via the chorioallantoic membrane. Birds and Reptiles Circulation Develops into the umbilical blood vessels. Humans and Mammals Organogenesis Contributes to the formation of the urinary bladder. : In humans, the allantois is largely vestigial

As human gestation progresses, the allantois undergoes a transformation:

myesr.org/poster/esr/ecr2020/C-10164/background">urachal cysts or other developmental remnants? Developmental Fate in Humans The is a critical

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