The anatomy of the normal placenta.

The placenta is the fetal organ providing the interchange between mother and fetus. This organ needs to provide its function such as transport and secretion even during its development and thus all developmental changes need to be in accordance with its function. This review describes development of the placenta during the first few weeks of pregnancy until the villous trees with their vasculature are established. The macroscopic anatomy of the delivered placenta as well as the microscopic anatomy and histology of this organ are also described. This includes the different types of villi and the most important cellular components of the villi such as villous trophoblast, Hofbauer cells, mesenchymal cells and endothelium. Fibrinoid and its localisation is also described.