Eventually, trophoblast cells destroy the wall of the maternal spiral arteries, converting them from muscular vessels into flaccid sinusoidal sacs lined with endovascular trophoblast Burrows et al. The aim of invasion is to reconstruct the maternal spiral arteries, which will maintain a high blood flow between the fetus and the mother, replacing small, high-resistance vessels with large, low-resistance vessels. The extent of trophoblastic invasion determines later placental efficiency and fetal viability in late gestation.
Deficiencies in trophoblastic invasion give rise to adverse pregnancy outcomes such as intrauterine growth restriction IUGR and preeclampsia Hunkapiller et al. Formation of placental villi is associated with remodeling of the extra-cellular matrix through tissue degradation and revision by various proteinases including serine proteases, matrix metalloproteinases MMPs and collagenases Cohen et al.
Serine proteases, including urokinase-type plasminogen activator uPA and tissue-type plasminogen activator tPA can catalyse the conversion of plasminogen to plasmin for proteolytic degradation of the ECM. Trophoblast cells express plasminogen activator receptors. Invasion and migration of mouse trophoblastic cells are closely related to their PA activity Strickland et al.
The zinc-dependent family of MMPs is a key player in matrix degradation during trophoblastic invasion. The MMP family is classified into three groups, including collagenases, gelatinases, and stromelysins based on the specificity of substrate.
Type IV collagen is a fundamental component of the basal membrane and it is one of the major structures of the uterine ECM Emonard et al. During early pregnancy, fetal trophoblast cells invade the uterus and penetrate the basement membrane, a property that is characteristic of malignant cells.
However, unlike tumor invasion, trophoblast invasion of the uterus should be under strict control confining the placenta and within the time constraint of a pregnancy. Limitation of trophoblastic invasion is attributed to the balance of activating and inhibiting growth factors, cytokines, and enzymes. In this article, we have discussed about various hormones and molecules involved in embryo implantation.
They are produced not only in a competent embryo but also in the epithelial and stromal compartments of the uterus. A complex dialogue between a receptive uterus and a competent blastocyst is continued during the implantation period. Many infertility problems have been overcome by a variety of assisted reproductive techniques.
Complete understanding of the molecular pathway of implantation will definitely improve the diagnosis and treatment of infertility. Sensitive and non-invasive methods to detect the embryo quality and endometrial receptivity will help to combat infertility which arises from defective implantation and decidualization. The authors declare that they have no conflicts of interest with respect to this study. National Center for Biotechnology Information , U. Journal List Dev Reprod v.
Dev Reprod. Published online Dec Su-Mi Kim 1 Dept. Jong-Soo Kim 1 Dept. Author information Article notes Copyright and License information Disclaimer. This article has been cited by other articles in PMC. Keywords: Implantation, Blastocyst, Endometrium, Uterine receptivity. The uterus then continues into the non- receptive period for the remaining cycle as the late luteal phase until menstruation ensues.
Preconditions for implantation To achieve successful implantation, the uterus should undergo structural and functional remodeling. Bischof P, Campana A. Trophoblast differentiation and invasion: its significance for human embryo implantation. Early Pregnancy. Trophoblast migration during human placental implantation. Hum Reprod Update. Mechanisms of implantation: strategies for successful pregnancy.
Nat Med. Heteromeric amino acid transporters: biochemistry, genetics, and physiology. Am J Physiol Renal Physiol. Metalloproteinases and human placental invasiveness. Heparin-binding EGF-like growth factor gene is induced in the mouse uterus temporally by the blastocyst solely at the site of its apposition: a possible ligand for interaction with blastocyst EGF-receptor in implantation.
Embryologic outcome and secretome profile of implanted blastocysts obtained after coculture in human endometrial epithelial cells versus the sequential system. Fertil Steril. New strategy for diagnosing embryo implantation potential by combining proteomics and time-lapse technologies.
Human endometrial CD98 is essential for blastocyst adhesion. PLoS One. Type IV and interstitial collagenolytic activities in normal and malignant trophoblast cells are specifically regulated by the extracellular matrix. Invasion Metastasis. Fukuda MN, Sugihara K. This implantation marks the commencement of pregnancy. In other words, until the implantation takes place, a woman is not regarded as pregnant.
To get an answer to this question, you will have to understand how you become pregnant. Here is a step by step guide:. In the case of in vitro fertilization IVF , the fertilized eggs or human blastocysts normally hatch out of their shell and start to implant about 1 or 2 days after the 5th day of the IVF blastocyst transfer.
This means the implantation takes place about 7 to 8 days after fertilization of the egg. The time required for implantation in both the cases, normal pregnancy and pregnancy through IVF, is more or less the same. How long does it take for the embryo to implant in the uterus? Here is a step by step guide: When you engage in unprotected sex, sperm passes through the vagina and get past the cervix to reach up to the fallopian tubes.
Here, a sperm is most likely to combine with an egg. When the sperm combines with the egg, fertilization takes place. The fertilized egg then travels up to the uterus for implantation. At the same time, it continues to grow in size even as its cells divide and reproduce. It is part of assisted reproductive technology ART.
The process…. Researchers have uncovered a link between conception and soda: drinking it daily could harm your chances of becoming pregnant. This goes for men and…. What to know about embryo transfers Medically reviewed by Nancy Choi, M. What is an embryo transfer? What to expect before, during, and after an embryo transfer. Types of embryo transfer. Share on Pinterest Studies suggest there may only be a small difference in success rates between fresh and frozen embryos used in IVF.
Risks and precautions of embryo transfers. Medically reviewed by Nancy Choi, M. Adolescent depression: Could school screening help? Related Coverage. IVF: What does it involve? Fertility preservation: What are women's options? Infertility in men and women. Medically reviewed by Debra Rose Wilson, Ph.
How does the egg donation process work? Once the blastocyst adheres to the uterine wall, the trophoblast secretes enzymes that digest the extracellular matrix of endometrial tissue.
The trophoblast cells then begin to intrude between the endometrial cells, attaching the blastocyst to the uterine surface. Further secretions of enzymes allow the blastocyst to bury itself deeply among the uterine stromal cells that form the structural components of the uterus. Subsequently, trophoblast cells continue to divide and form two extraembryonic membranes. These membranes form the fetal portion of the placenta called the chorion. Additional enzymes and signaling factors secreted by these membranes remodel the uterine vasculature to bathe the fetal or embryonic blood vessels in maternal blood.
Chorionic villi are the folds of tissue and blood vessels that connect maternal and fetal blood pools. Maternal blood diffuses into the villi, and it travels through them into the fetus 's vasculature. Similarly, fetal blood diffuses from the villi and into the maternal vasculature. Normally fetal and maternal blood do not mix, but the relationship between the two circulatory systems enables the transfer of nutrients and oxygen to the fetus or embryo, and carbon dioxide and urea from the fetus to the mother.
While unique to mammals as a reproductive process, implantation is not unique to the uterus and the trophoblast. In the s, researchers found similarities between the invasive abilities of blastocysts and those of cancer cells. The same trophoblast enzymes that digest the endometrium are also used by tumor cells to burrow into tissues throughout body. Tumor cells use the same growth factors as the trophoblast to attract maternal blood vessels, which then interact with the chorion , and to provide nutrients to the expanding mass.
In addition, the changes in the endometrium during decidualization such as swelling, the accumulation of white blood cells, and the general activation of the maternal immune system, are consistent with a response to the presence of pathogens or tumors. Keywords: Reproduction , Human development , Fertilization.
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