Trophoblast

Trophoblast

Diagram of a blastocyst stage embryo, showing the trophoblast.

The trophoblast is a layer of tissue on the outside of a mammalian blastocyst, supplying the embryo with nourishment and later forming a major part of the placenta. It is the first cell lineage to differentiate from the fertilized egg and plays a crucial role in implantation and interaction with the maternal endometrium.

Development

Embryonic disc, amniotic cavity, and yolk sac.

The trophoblast differentiates from the outer layer of the blastocyst during early embryogenesis. It surrounds the inner cell mass and the blastocoel, and it is responsible for the implantation of the embryo into the uterine wall. The trophoblast further differentiates into two layers: the cytotrophoblast and the syncytiotrophoblast.

Cytotrophoblast

The cytotrophoblast is the inner layer of the trophoblast, consisting of individual cells that retain their cell membranes. It serves as a source of new cells for the syncytiotrophoblast.

Syncytiotrophoblast

The syncytiotrophoblast is the outer layer of the trophoblast, which is a multinucleated cell mass that invades the uterine wall to establish nutrient circulation between the embryo and the mother. It secretes enzymes that allow the blastocyst to penetrate the uterine lining.

Function

Illustration of early stages of human development.

The primary function of the trophoblast is to facilitate the exchange of nutrients and waste products between the mother and the developing embryo. It also produces hormones such as human chorionic gonadotropin (hCG), which is crucial for maintaining the corpus luteum and the early stages of pregnancy.

Pathology

Histopathology of a tubal pregnancy showing trophoblastic tissue.

Abnormalities in trophoblast development can lead to pregnancy complications such as preeclampsia, gestational trophoblastic disease, and ectopic pregnancy. In ectopic pregnancies, the trophoblast implants outside the uterine cavity, often in the fallopian tube, leading to potential rupture and hemorrhage.

Related pages

• Embryogenesis
• Placenta
• Implantation (human embryo)

References

• 
  Diagram of Blastocyst stage
• 
  Embryonic Disc, Amniotic Cavity, Yolk Sac
• 
  Trophoblast
• 
  Trophoblast
• 
  Trophoblast
• 
  Trophoblast
• 
  Human Embryogenesis
• 
  Histopathology of tubal pregnancy