Definition of Yolk sac
Yolk sac: Not all yolk has to do with birds' eggs. Human embryos have a yolk sac, too. The human yolk sac is a membrane outside the embryo that is connected by a tube (the yolk stalk) though the umbilical opening to the embryo's midgut. The yolk sac serves as an early site for the formation of blood and in time, is incorporated into the primitive gut of the embryo.Source: MedTerms™ Medical Dictionary
Last Editorial Review: 9/20/2012
Medical Dictionary Definitions A - Z
Search Medical Dictionary
Pregnancy and Parenting Resources
- 10 Tips to Soothe a Crying Baby
- What to Know Before You Get Pregnant
- Pregnancy: What Does Insurance Cover?
- Symptoms of a Severe Allergic Reaction
- Breast Cancer Treatment Options
- Is Your Body Ready for Pregnancy?