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The amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo until shortly before birth. The inner of these membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the embryo. The outer membrane, the chorion, contains the amnion and is part of the placenta. On the outer side, the amniotic sac is connected to the yolk sac, the allantois, and via the umbilical cord, the placenta.
Gastrulation is the stage in the early embryonic development of most animals, during which the blastula, or in mammals the blastocyst is reorganized into a two-layered or three-layered embryo known as the gastrula. Before gastrulation, the embryo is a continuous epithelial sheet of cells; by the end of gastrulation, the embryo has begun differentiation to establish distinct cell lineages, set up the basic axes of the body, and internalized one or more cell types including the prospective gut.
The blastocyst is a structure formed in the early embryonic development of mammals. 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. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocoel. In the late blastocyst the trophectoderm is known as the trophoblast. The trophoblast gives rise to the chorion and amnion, the two fetal membranes that surround the embryo. The placenta derives from the embryonic chorion and the underlying uterine tissue of the mother.
The blastocoel, also spelled blastocoele and blastocele, and also called cleavage cavity, or segmentation cavity is a fluid-filled or yolk-filled cavity that forms in the blastula during very early embryonic development. At this stage in mammals the blastula develops into the blastocyst containing an inner cell mass, and outer trophectoderm.
A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans produce two or three primary germ layers. Some animals, like cnidarians, produce two germ layers making them diploblastic. Other animals such as bilaterians produce a third layer between these two layers, making them triploblastic. Germ layers eventually give rise to all of an animal's tissues and organs through the process of organogenesis.
Embryoid bodies (EBs) are three-dimensional aggregates of pluripotent stem cells.
Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major constituents of the basement membrane, namely the basal lamina. Laminins are vital to biological activity, influencing cell differentiation, migration, and adhesion.
Syncytiotrophoblast is the epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother. It is a multinucleate, terminally differentiated syncytium, extending to 13 cm.
Placentation refers to the formation, type and structure, or arrangement of the placenta. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing embryo, and in some instances to remove waste from the embryo. Placentation is best known in live-bearing mammals (theria), but also occurs in some fish, reptiles, amphibians, a diversity of invertebrates, and flowering plants. In vertebrates, placentas have evolved more than 100 times independently, with the majority of these instances occurring in squamate reptiles.
"Cytotrophoblast" is the name given to both the inner layer of the trophoblast or the cells that live there. It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo.
In amniote embryonic development, the epiblast is one of two distinct cell layers arising from the inner cell mass in the mammalian blastocyst, or from the blastula in reptiles and birds, the other layer is the hypoblast. It drives the embryo proper through its differentiation into the three primary germ layers, ectoderm, mesoderm and endoderm, during gastrulation. The amniotic ectoderm and extraembryonic mesoderm also originate from the epiblast.
Implantation, also known as nidation is the stage in the embryonic development of mammals in which the blastocyst hatches, attaches, adheres, and invades into the wall of the female's uterus. Implantation is the first stage of gestation, and, when successful, the female is considered to be pregnant. An implanted embryo is detected by the presence of increased levels of human chorionic gonadotropin (hCG) in a pregnancy test. The implanted embryo will receive oxygen and nutrients in order to grow.
The bilaminar embryonic disc, bilaminar blastoderm or embryonic disc is the distinct two-layered structure of cells formed in an embryo. In the development of the human embryo this takes place by day eight. It is formed when the inner cell mass, also known as the embryoblast, forms a bilaminar disc of two layers, an upper layer called the epiblast and a lower layer called the hypoblast, which will eventually form into fetus. These two layers of cells are stretched between two fluid-filled cavities at either end: the primitive yolk sac and the amniotic sac.
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 to endometrial stromal cells (ESCs), the presence of decidual white blood cells (leukocytes), and vascular changes to maternal arteries. The sum of these changes results in the endometrium changing into a structure called the decidua. In humans, the decidua is shed during childbirth.
Human embryonic development, or human embryogenesis, is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, the development of the human body entails growth from a one-celled zygote to an adult human being. Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form the single cell zygote and the germinal stage of development commences. Embryonic development in the human, covers the first eight weeks of development; at the beginning of the ninth week the embryo is termed a fetus. The eight weeks has 23 stages.
In amniote embryology, the hypoblast is one of two distinct layers arising from the inner cell mass in the mammalian blastocyst, or from the blastodisc in reptiles and birds. The hypoblast gives rise to the yolk sac, which in turn gives rise to the chorion.
The fetal membranes are the four extraembryonic membranes, associated with the developing embryo, and fetus in humans and other mammals. They are the amnion, chorion, allantois, and yolk sac. The amnion and the chorion are the chorioamniotic membranes that make up the amniotic sac which surrounds and protects the embryo. The fetal membranes are four of six accessory organs developed by the conceptus that are not part of the embryo itself, the other two are the placenta, and the umbilical cord.
Cell potency is a cell's ability to differentiate into other cell types. The more cell types a cell can differentiate into, the greater its potency. Potency is also described as the gene activation potential within a cell, which like a continuum, begins with totipotency to designate a cell with the most differentiation potential, pluripotency, multipotency, oligopotency, and finally unipotency.
Laminin–111 is a protein of the type known as laminin isoforms. It was among the first of the laminin isoforms to be discovered. The "111" identifies the isoform's chain composition of α1β1γ1. This protein plays an important role in embryonic development. Injections of this substance are used in treatment for Duchenne muscular dystrophy, and its cellular action may potentially become a focus of study in cancer research.
Preimplantation factor(PIF) is a peptide secreted by trophoblast cells prior to placenta formation in early embryonic development. Human embryos begin to express PIF at the 4-cell stage, with expression increasing by the morula stage and continuing to do so throughout the first trimester. Expression of preimplantation factor in the blastocyst was discovered as an early correlate of the viability of the eventual pregnancy. Preimplantation factor was identified in 1994 by a lymphocyte platelet-binding assay, where it was thought to be an early biomarker of pregnancy. It has a simple primary structure with a short sequence of fifteen amino acids without any known quaternary structure. A synthetic analogue of preimplantation factor (commonly abbreviated in studies as sPIF or PIF*) that has an identical amino acid sequence and mimics the normal biological activity of PIF has been developed and is commonly used in research studies, particularly those that aim to study potential adult therapeutics.
References
- ↑ Smith, KK; Strickland, S (10 May 1981). "Structural components and characteristics of Reichert's membrane, an extra-embryonic basement membrane". The Journal of Biological Chemistry. 256 (9): 4654–61. doi: 10.1016/S0021-9258(19)69485-8 . PMID 6260808.
- 1 2 3 Ueda, Yoko; Kimura-Yoshida, Chiharu; Mochida, Kyoko; Tsume, Mami; Kameo, Yoshitaka; Adachi, Taiji; Lefebvre, Olivier; Hiramatsu, Ryuji; Matsuo, Isao (19 May 2020). "Intrauterine Pressures Adjusted by Reichert's Membrane Are Crucial for Early Mouse Morphogenesis". Cell Reports. 31 (7): 107637. doi: 10.1016/j.celrep.2020.107637 . hdl: 2433/260943 . PMID 32433954. S2CID 218766117.
- ↑ "Reichert's membrane - Ontology Browser - Rat Genome Database". rgd.mcw.edu. Retrieved 5 September 2022.
- ↑ Miner, JH; Yurchenco, PD (2004). "Laminin functions in tissue morphogenesis". Annual Review of Cell and Developmental Biology. 20: 255–84. doi:10.1146/annurev.cellbio.20.010403.094555. PMID 15473841.
- ↑ Weberling, A; Zernicka-Goetz, M (19 January 2021). "Trophectoderm mechanics direct epiblast shape upon embryo implantation". Cell Reports. 34 (3): 108655. doi:10.1016/j.celrep.2020.108655. PMC 7816124 . PMID 33472064.