Yolk sac

Definition

The yolk sac is a membranous structure attached to the embryo that provides early nourishment in the form of yolk. It is crucial for the development of certain vertebrates, including reptiles, during their embryonic stages.

5 Must Know Facts For Your Next Test

1. The yolk sac supplies nutrients to the developing embryo before the placenta forms in placental animals or before hatching in oviparous animals like reptiles.
2. In reptiles, the yolk sac is rich in proteins and lipids essential for growth and development.
3. The vascularization of the yolk sac allows for efficient nutrient transfer to the embryo.
4. As development progresses, the role of the yolk sac diminishes, and it is eventually absorbed or reduced in size.
5. Abnormalities in yolk sac function can lead to developmental issues or embryonic lethality.

Review Questions

• What primary function does the yolk sac serve during early reptilian embryonic development?
• How does the yolk sac contribute to nutrient transfer in reptile embryos?
• Why is vascularization important for the functioning of the yolk sac?

Related terms

Chorion:

A membrane that surrounds all other membranes and structures within an egg, involved in gas exchange.

Amnion:

A membranous structure that encloses and protects an embryo within an amniotic cavity filled with fluid.

Allantois:

A membrane involved in respiration and excretion, also playing a role in forming blood vessels within an egg.