The foetal blood is separated from syncytiotrophoblast with all except :
Ans. is d i.e. Decidua parietalis Friends, once again we will have to peep into embryology to answer this question. Formation of placenta : Placenta is formed by the trophoblast. The trophoblast is made up of a single layer of cells. Cells of trophoblast multiply to form distinct layers. The cells that are near to the decidua lose their cell boundaries to form syncytium. This layer of the trophoblast is known as the syncytiotrophoblast. Deep to the syncytium, the cells of the trophobiast retain their cell walls and form the second layer called as the cyto trophoblast. The cyto trophobiast rests on the mesoderm. Small cavities appear in the syncytiotrophoblast called as Lacunae. The lacunae are separated from one another by paitions of syncytium called as trabeculae. The syncytiotrophoblast grows into the endometrium (Decidua). As the endometrium is eroded. some of the maternal blood vessels are opened up and blood from them fills the lacunar space. So. lacunae have maternal blood. Each trabeculas is, initially made up entirely of syncytiotrophoblast. Later cells of cytotrophoblast begin to multiply and grow into each trabeculas. This is called as Primary Extra embryonic mesoderm then invades the centre of each primary villus. This is now called as secondary villus. Soon thereafter. fetal blood vessels can be seen in the mesoderm forming the core of each villus. The villus is called as Teiary villus. Thus the maternal blood in the lacuna is never in direct contact with fetal blood. They are separated by 1. Syncytiotrophoblast 1 2. Cytotrophoblast Together k/a 3. Basement membrane placental 4. Mesoderm barrier or 5. Endothelium of fetal capillaries 1 membrane
Fetal blood capillary membrane
Mesenchyme of intervillous blood space
Cytotrophoblast
Decidua parietalis