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The functional layer of the endometrial lining undergoes cyclic regeneration from stem cells in the basal layer. [1] Humans, apes, and some other species display the menstrual cycle, whereas most other mammals are subject to an estrous cycle. [2] In both cases, the endometrium initially proliferates under the influence of estrogen.
Layer Location Description Cytotrophoblast: The inner layer: A single-celled inner layer of the trophoblast. Syncytiotrophoblast: The outer layer: 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)
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 epiblast is the outer layer of the bilaminar embryonic disc and consists of columnar cells.
From innermost to outermost, these layers are the endometrium, myometrium, and perimetrium. [7] The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer; the functional layer thickens and then is shed during the menstrual cycle or estrous cycle.
It possesses an inner cell mass (ICM) also known as the embryoblast which subsequently forms the embryo, and an outer layer of trophoblast cells called the trophectoderm. [1] [2] This layer surrounds the inner cell mass and a fluid-filled cavity or lumen known as the blastocoel. [3] In the late blastocyst, the trophectoderm is known as the ...
The trophoblast will also develop two sub-layers: the cytotrophoblast, which is in front of the syncytiotrophoblast, which in turn lies within the endometrium. [10] Next, another layer called the exocoelomic membrane or Heuser's membrane will appear and surround the cytotrophoblast, as well as the primitive yolk sac. [11]
In humans it is formed by extraembryonic mesoderm and the two layers of trophoblast that surround the embryo and other membranes; [1] the chorionic villi emerge from the chorion, invade the endometrium, and allow the transfer of nutrients from maternal blood to fetal blood.
This layer is absent in placenta accreta. [2] Micrograph of decidualized endometrium due to exogenous progesterone. H&E stain. The decidua has a histologically-distinct appearance, displaying large polygonal decidual cells in the stroma. These are enlarged endometrial stromal cells, which resemble epithelium (and are referred to as "epithelioid").