Chorionic villi are villi that sprout from the

chorion The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). It develops from an outer fold on the surface of the yolk sac, which lies outside the zona pellucida (in mammals), known as the vitelline ...

to provide maximal contact area with maternal blood. They are an essential element in

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

from a histomorphologic perspective, and are, by definition, a product of conception. Branches of the

umbilical arteries The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord. Structure Development The umbilical arteries supply deoxygenated bl ...

carry embryonic blood to the villi. After circulating through the capillaries of the villi, blood returns to the embryo through the

umbilical vein The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus. The umbilical vein provides convenient access to the central circulation of a neonate for restoration of blood vo ...

. Thus, villi are part of the border between maternal and fetal blood during pregnancy.

Structure

Villi can also be classified by their relations: * Floating villi float freely in the intervillous space. They exhibit a bi-layered epithelium consisting of

cytotrophoblast "Cytotrophoblast" is the name given to both the inner layer of the trophoblast (also called layer of Langhans) or the cells that live there. It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo ...

s with overlaying

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

(

syncytiotrophoblast Syncytiotrophoblast (from the Greek 'syn'- "together"; 'cytio'- "of cells"; 'tropho'- "nutrition"; 'blast'- "bud") is the epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nut ...

). * Anchoring (stem) villi stabilize mechanical integrity of the placental-maternal interface.

Development

The

undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo. They undergo several stages, depending on their composition. Until about the end of the second month of

, the villi cover the entire chorion, and are almost uniform in size—but after then, they develop unequally.

Microanatomy

The bulk of the villi consist of connective tissues that contain blood vessels. Most of the cells in the connective tissue core of the villi are fibroblasts. Macrophages known as

Hofbauer cells Hofbauer cells are oval eosinophilic histiocytes with granules and vacuoles found in the placenta, which are of mesenchymal origin, in mesoderm of the chorionic villus, particularly numerous in early pregnancy. Etymology They are named after J. ...

are also present.

Clinical significance

Use for prenatal diagnosis

In 1983, an Italian biologist named Giuseppe Simoni discovered a new method of prenatal diagnosis using chorionic villi.

Stem cell

Chorionic villi are a rich source of

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type o ...

Biocell Center Biocell Center is an international company specializing in the cryopreservation and private banking of amniotic fluid stem cells. The company is headquartered in Italy with several international locations and is involved with numerous partnerships ...

, a biotech company managed by Giuseppe Simoni, is studying and testing these types of stem cells. Chorionic stem cells, like

amniotic stem cells Amniotic stem cells are the mixture of stem cells that can be obtained from the amniotic fluid as well as the amniotic membrane. They can develop into various tissue types including skin, cartilage, cardiac tissue, nerves, muscle, and bone. The cell ...

, are uncontroversial multipotent stem cells.

Infections

Recent studies indicate that the chorionic villi may be susceptible to bacterial and viral infections. Recents findings indicate that ureaplasma parvum can infect the chorionic villi tissues of pregnant women, thereby impacting pregnancy outcome. DNA from

JC polyomavirus ''Human polyomavirus 2'', commonly referred to as the JC virus or John Cunningham virus, is a type of human polyomavirus (formerly known as papovavirus). It was identified by electron microscopy in 1965 by ZuRhein and Chou, and by Silverman an ...

and

Merkel cell polyomavirus Merkel cell polyomavirus (MCV or MCPyV) was first described in January 2008 in Pittsburgh, Pennsylvania. It was the first example of a human viral pathogen discovered using unbiased metagenomic next-generation sequencing with a technique called d ...

has been detected in chorionic villi from pregnant women and women affected by

miscarriage Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...

. DNA from

BK polyomavirus The BK virus is a member of the polyomavirus family. Past infection with the BK virus is widespread, but significant consequences of infection are uncommon, with the exception of the immunocompromised and the immunosuppressed. BK virus is an ab ...

has also been detected in the same tissues but to a lesser extent.

Early miscarriage

Gross pathology of fixed chorionic villi

In early miscarriage, the finding of chorionic villi in vaginal expulsions is often the only definite confirmation that there was an intrauterine pregnancy rather than an

ectopic pregnancy Ectopic pregnancy is a complication of pregnancy in which the embryo attaches outside the uterus. Signs and symptoms classically include abdominal pain and vaginal bleeding, but fewer than 50 percent of affected women have both of these symptoms. ...

Additional images

File:Chorionic villi - intermed mag.jpg,

Micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a mic ...

showing chorionic villi. Intermediate magnification.

H&E stain Hematoxylin and eosin stain ( or haematoxylin and eosin stain or hematoxylin-eosin stain; often abbreviated as H&E stain or HE stain) is one of the principal tissue stains used in histology. It is the most widely used stain in medical diagnos ...

. File:Chorionic villi - very high mag.jpg,

showing chorionic villi. Very high magnification.

. File:Gray21.png, Section through the embryo. File:Gray35.png, Transverse section of a chorionic villus. File:Gray459.png, Human embryo of about 28 days, with yolk-sac.

References

External links

* http://www.med.umich.edu/lrc/coursepages/M1/embryology/embryo/06placenta.htm Embryology {{Portal bar, Anatomy