Final answer:
The amnion, chorion, yolk sac, and allantois are extraembryonic structures vital for embryonic development, providing nourishment, protection, gas exchange, and waste management.
Step-by-step explanation:
The Amnion, Chorion, Yolk Sac, and Allantois
The amnion, chorion, yolk sac, and allantois are extraembryonic structures that play critical roles in the development of an embryo in amniotes, including mammals, reptiles, and birds. These structures form around and support the embryo as it grows within the uterus or an egg.
- The yolk sac provides nourishment to the early embryo and is involved in the creation of germ and blood cells once the placenta takes over the role of nutrient and waste exchange.
- The amnion is a protective membrane that forms a sac filled with amniotic fluid, cushioning the embryo from mechanical shock and maintaining hydration.
- The chorion is involved in the gas exchange between the embryo and the external environment and, along with the allantois, forms part of the placenta in mammals.
- The allantois stores nitrogenous waste and facilitates respiration. In the human embryo, the allantois becomes part of the urinary bladder and contributes to the formation of the umbilical cord.
In the context of an amniotic egg, such as those laid by birds and reptiles, these membranes have adaptations that enable the embryo to develop in a terrestrial environment, providing protection and contributing to the various needs of the growing embryo.