2nd Week of Development, Life Inside the Womb
The yolk sac covering is a layer of extraembryonic visceral mesodermal cells. In addition to the yolk sac, two further extraembryonic coeloms form during the second week, the amniotic cavity and the chorionic cavity. Read to know more.
Nivedita Dar4 Jul, 2024
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2nd Week of Development: Life Inside the Womb
After the fertilization of male and female gametes, the development from embryo to fetus is a meticulously orchestrated process that progresses through various stages. The critical processes of implantation, formation of the bilaminar embryonic disc, and the creation of extraembryonic structures occur during this period. This time is essential for establishing the embryo’s basic structure and support systems.Implantation into the Endometrium
One of the most critical events during the second week is implantation. By the end of the first week, the morula—a ball of cells—undergoes changes, including the development of a cyst that transforms it into a blastocyst. The blastocyst consists of an outer layer of cells called the trophoblast, which will eventually form the placenta, and an inner cell mass that will develop into the embryo. The blastocyst embeds itself into the endometrium, the lining of the uterus. This process, known as implantation, leads to the differentiation of the trophoblast into two layers: the cytotrophoblast and the syncytiotrophoblast. The invasion of the endometrial tissue by the syncytiotrophoblast connects the developing embryo with the maternal blood supply, facilitating the removal of waste products and the renewal of oxygen and nutrients. Simultaneously, the inner cell mass also differentiates into two distinct layers, forming the bilaminar embryonic disc. These layers are the epiblast and the hypoblast. The epiblast will give rise to the embryo proper, while the hypoblast contributes to the formation of extraembryonic structures such as the yolk sac.Differentiation
Differentiation is the process by which cells mature and their final fate is decided. Every cell in the embryo divides and divides until it finally gives rise to a terminal cell that becomes part of an organ.Extraembryonic Structures: The Membranes Which Cradle Life Inside
Extraembryonic structures, such as the amniotic cavity, develop in the second week of development. The amniotic cavity forms within the epiblast. This fluid-filled cavity will eventually surround the embryo, providing a protective cushion and maintaining a stable environment for its development. The yolk sac, derived from the hypoblast, is another important extraembryonic structure. Although its role in human development is limited compared to other species, it contributes to the early formation of blood cells and vessels and serves as a site for nutrient exchange before the placenta is fully established.Formation of Primitive Uteroplacental Circulation
The formation of the blood connection between the mother and the embryo continues to develop in the second week. As the syncytiotrophoblast invades the maternal endometrium, it creates lacunae, or small spaces, within its structure. These lacunae fill with maternal blood, establishing the primitive uteroplacental circulation.2nd Week of Development, Life Inside the Womb FAQs
What is abortion?
Abortion is the medical or surgical termination of a pregnancy before the fetus can live independently outside the mother’s womb. It can occur spontaneously, known as a miscarriage, or be induced for various reasons.
What is a urine test for pregnancy?
A urine test for pregnancy detects the presence of human chorionic gonadotropin (hCG), a hormone produced during pregnancy. This test is commonly used to confirm pregnancy at home or in a clinical setting.
What is placenta previa?
Placenta previa is a condition where the placenta partially or completely covers the cervix, the opening of the uterus. This can cause severe bleeding during pregnancy and delivery and often requires medical management or surgical intervention.
What is ectopic pregnancy?
An ectopic pregnancy occurs when a fertilized egg implants and grows outside the main cavity of the uterus, often in a fallopian tube. This type of pregnancy is not viable and can be life-threatening to the mother if not treated promptly.
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