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What is the difference between primary secondary and tertiary villi?

Published in Placental Development 2 mins read

The primary, secondary, and tertiary villi represent stages in the development of placental villi, distinguished by their structural components and the presence of blood vessels.

Here's a breakdown of the key differences:

Placental Villi Development

The development of placental villi is a crucial process for fetal nourishment. The villi increase the surface area available for the exchange of nutrients and waste between the maternal and fetal blood.

Primary Villi

  • Development Stage: These are the initial extensions formed during placental development. According to the reference, these extensions are the first stage.
  • Structure: They consist of an outer layer of cytotrophoblast and an inner layer of syncytiotrophoblast, without any mesenchymal core.

Secondary Villi

  • Development Stage: These evolve from primary villi.
  • Structure: The defining characteristic of a secondary villus is the appearance of a mesenchymal core within the expanding villus. The reference notes that the secondary villus is characterized by the appearance of this core. This core provides structural support.

Tertiary Villi

  • Development Stage: These develop from secondary villi.
  • Structure: A secondary villus becomes a tertiary villus when blood vessels penetrate the mesenchymal core and newly formed branches. The reference states that blood vessels penetrate the mesenchymal core. This vascularization is essential for nutrient and waste exchange.

Summary Table

Feature Primary Villi Secondary Villi Tertiary Villi
Key Feature Initial extensions Mesenchymal core appearance Blood vessel penetration into mesenchymal core
Outer Layer Cytotrophoblast, Syncytiotrophoblast Cytotrophoblast, Syncytiotrophoblast Cytotrophoblast, Syncytiotrophoblast
Inner Core None Mesenchymal core Mesenchymal core with blood vessels
Function Initial placental structure formation Structural support, further development Nutrient and waste exchange