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Implantation bleeding occurs between 7 and 14 days after fertilization, [57] and is a small amount of light vaginal bleeding or spotting that can occur in early pregnancy due to the blastocyst penetrating the lining of the uterus during implantation.
Once bound to the extracellular matrix of the endometrium, trophoblast cells secrete enzymes and other factors to embed the blastocyst into the uterine wall. The enzymes released degrade the endometrial lining, while autocrine growth factors such as human chorionic gonadotropin (hCG) and insulin-like growth factor (IGF) allow the blastocyst to ...
The early embryo has 1–2 weeks in order to produce sufficient hCG in order to stabilize the endometrial lining to allow for blastocyst attachment. The dramatic increase in trophoblastic and corpus luteal hCG synthesis signals both blastocyst [5] and corpus luteal [6] production of P4, crucial for the maintenance of the endometrium.
Once the blastocyst is formed, it undergoes implantation into the endometrium. [4] During implantation the blastocyst, which contains the inner cell mass, undergoes cellular differentiation into the two layers of the bilaminar embryonic disc. One of which is the epiblast, also known as the primitive ectoderm.
The structure is then termed a blastula, or a blastocyst in mammals. The mammalian blastocyst hatches before implantating into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of gastrulation, neurulation, and organogenesis.
This lining of the uterine cavity (or womb) is now known as the decidua, and it produces a great number of large decidual cells in its increased interglandular tissue. The blastomeres in the blastocyst are arranged into an outer layer called the trophoblast .
A thick layer that lacks cell boundaries and grows into the endometrial stroma. It secretes hCG in order to maintain progesterone secretion and sustain a pregnancy. Intermediate trophoblast (IT) The implantation site, chorion, villi (dependent on subtype) An anchor placenta (implantation site IT).
Decidualization is a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy. This includes morphological and functional changes (the decidual reaction) to endometrial stromal cells (ESCs), the presence of decidual white blood cells (leukocytes), and vascular changes to maternal arteries.