Syncytiotrophoblast (from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

'syn'- "together"; 'cytio'- "of cells"; 'tropho'- "nutrition"; 'blast'- "bud") is the epithelial covering of the highly vascular

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

nic

placenta The placenta is a temporary embryonic and later fetal organ (anatomy), organ that begins embryonic development, developing from the blastocyst shortly after implantation (embryology), implantation. It plays critical roles in facilitating nutrien ...

l villi, which invades the wall of the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

to establish nutrient circulation between the embryo and the mother. It is a multi-nucleate, terminally differentiated

syncytium A syncytium (; plural syncytia; from Ancient Greek, Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell (biology), cell which can result from multiple cell fusions of uninuclear cells (i.e ...

, extending to 13cm.

Function

2907 Embroyonic Disc, Amniotic Cavity, Yolk Sac-02

It is the outer layer of the trophoblasts and actively invades the uterine wall, during implantation, rupturing maternal

capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

and thus establishing an interface between maternal blood and embryonic extracellular fluid, facilitating passive exchange of material between the mother and the embryo. The syncytial property is important since the mother's

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as Tumor immunology, cancer cells and objects such ...

includes white blood cells that are able to migrate into tissues by "squeezing" in between cells. If they were to reach the fetal side of the placenta many foreign proteins would be recognised, triggering an immune reaction. However the syncytium acts as a giant cell so there are no gaps for immune cells to migrate through. One way in which it accomplishes this task is by suppressing the expression of immunity-related genes HLA-A and HLA-B, which are classically known to be expressed by all nucleated cells. These genes normally express the MHC-I ligand that acts as a major binding mechanism for T-cells. By decreasing the translation of these gene products, the syncytiotrophoblast reduces the chances of an attack by the maternal immune system mediated by T-cells. The syncytiotrophoblast secretes

progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...

and leptin in addition to human chorionic gonadotropin (hCG) and human placental lactogen (HPL); hCG prevents degeneration of the corpus luteum. Progesterone serves to maintain the integrity of the

uterine lining 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 basal layer contains stem cells which regenerate the functional layer. The functional layer ...

and, until the syncytiotrophoblast is mature enough to secrete enough progesterone to support pregnancy (in the fourth month of embryonic development), it is aided by the corpus luteum graviditatis.

Formation

The syncytiotrophoblast lacks proliferative capacity and instead is maintained by fusion of underlying cytotrophoblast cells. This fusion is assisted by syncytin, a protein that was integrated into mammalian genomes from an endogenous retrovirus.

Additional images

Image:Gray12.png, Section through embryonic area of Vespertilio murinus to show the formation of the amniotic cavity. Image:Histopathology of tubal pregnancy.jpg, Histopathology of a chorionic villus, in a tubal pregnancy

References

Tony M. Plant, Anthony J. Zeleznik: "Knobil and Neill's Physiology of Reproduction: Two-Volume Set" p 1790

External links

* - "Female Reproductive System: placental villi"
''Nature (Journal) Diagram''
*
Article

{{Authority control Non-terminally differentiated (blast) cells Embryology Human female endocrine system

Function

Formation

Additional images

See also

References

External links