The main difference between yolk sac and gestational sac is their order of appearance in early pregnancy and the time at which they become visible in the uterus. The yolk sac becomes visible in the uterus during early pregnancy at around 5.5 weeks, making it the second structure to appear. On the other hand, the gestational sac is the first structure to be detected in the uterus during early pregnancy, becoming visible at around 5 weeks.
The yolk sac and gestational sac are two structures that play different roles in early pregnancy. Implantation takes place during the second week of embryonic development. At this stage, the conceptus, which is formed from the fertilized egg, is called the blastocyst. The blastocyst later organizes into four extra embryonic membranes, namely the yolk sac, chorion, amnion, and allantois. The function of each membrane is to provide support for the developing embryo.
Key Areas Covered
1. What is the Yolk Sac
– Definition, Location, Function
2. What is the Gestational Sac
– Definition, Location, Function
3. Similarities Between Yolk Sac and Gestational Sac
– Outline of Common Features
4. Difference Between Yolk Sac and Gestational Sac
– Comparison of Key Differences
Key Terms
Gestational Sac, Yolk Sac
What is the Yolk Sac
The yolk sac is a membranous sac that is attached to the developing embryo by a yolk stalk. It is filled with yolk. Yolk is a mixture of proteins, lipids, and other nutrients necessary for the embryo’s growth and development; hence, it serves as a primary source of nutrients for the development of the embryo. The yolk sac is round or pear-shaped. It appears like a ring with a white rim and black interior. The size of the yolk sac is around 3-5 millimeters. The size of the yolk sac helps to determine how far you are in your pregnancy. Moreover, the yolk sac is present in the gestational sac.
There are many functions of the yolk sac. Some of them include creating the first form of blood cells, creating the cells that convert to other important structures, providing nutrients to the baby, circulating the gasses between the baby and the pregnant mother, and providing the baby with metabolism and immune functions. As the embryo develops, the yolk sac becomes less important. Later, the placenta takes its functions.
What is the Gestational Sac
The gestational sac is a fluid-filled structure surrounding an embryo during the first few weeks of embryonic development. It is the first visible sign of pregnancy on ultrasound. It typically appears around 4-5 weeks after the last menstrual period. The gestational sac is a spherical-shaped structure located in the upper part of the uterus. It is around 20-25 mm in size. The size of this structure can help to determine the gestational age of the pregnancy. The size and shape of the gestational sac are also useful in monitoring the progress of the pregnancy and identifying the problems.
The gastrointestinal sac forms when the fertilized egg implants in the lining of the uterus. This sac composes a fluid that protects the developing embryo. Moreover, there is a connection between the gestational sac and the placenta, which provides the nutrients and oxygen required for embryo development.
If the size of the gestational sac is small, it can be a sign of very early pregnancy or a possible miscarriage. Having a large gestational sac may be a sign of a miscalculated due date or a pregnancy that is further along than originally thought.
Similarities Between Yolk Sac and Gestational Sac
- Both the yolk sac and gestational sac are structures in embryonic development.
Difference Between Yolk Sac and Gestational Sac
Definition
The yolk sac is a membranous sac that is attached to the developing embryo by a yolk stalk, while the gestational sac is a fluid-filled structure that encloses a developing embryo during the very early stages of pregnancy.
Development
The yolk sac becomes visible in the uterus during early pregnancy at around 5.5 weeks, making it the second structure to appear. The gestational sac, on the other hand, is the first structure to be detected in the uterus during early pregnancy, becoming visible at around 5 weeks.
Size
Moreover, the size of the yolk sac is 3-5mm, while the size of the gestational sac is 20-25 mm.
Location
The yolk sac is located in the front part of the embryo, whereas the gestational sac is located in the upper part of the uterus.
Function
Functions of the yolk sac include helping the circulation of gases between the mother and the embryo, providing the embryo with nourishments, and producing cells that convert into important structures such as the umbilical cord. However, the gestational sac helps to determine whether an intrauterine pregnancy exists (till identifying the embryo ) and provides protection to the embryo.
Conclusion
Both the yolk sac and the gestational sac are structures found in embryonic development. The yolk sac is a membranous sac that is attached to the developing embryo by a yolk stalk, while the gestational sac is a fluid-filled structure surrounding an embryo during the first few weeks of embryonic development. Therefore, the main difference between yolk sac and gestational sac is their order of appearance in early pregnancy and the time at which they become visible in the uterus.
Reference:
1. “Embryology, Yolk Sac.” National Library of Medicine.
2. “Gestational sac.” Radiopaedia.
Image Courtesy:
1. “Human Yolk Sac from Tubal Pregnancy” By Ed Uthman (CC BY 2.0) via Flickr
2. “4 mm gestational sac” By Luis Goncalves – Own work (CC BY-SA 3.0) via Commons Wikimedia
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