The structure of a placenta is complex, designed for efficient nutrient and waste exchange between mother and fetus. A mature placenta, weighing roughly 500-600 grams, is composed of several key components.
Cotyledons: The Building Blocks
The placenta is organized into 15–28 "cotyledons." These cotyledons are the functional units of the placenta.
The Villous Tree: Fetal Side Structure
Each cotyledon's structure stems from the stem villus. The structure is made up of:
- Stem Villus: This is the major structural unit from which everything else branches.
- Intermediate Villi: Each stem villus divides into 3-5 immature/mature intermediate villi.
- Terminal Villi: The intermediate villi further branches into 10–12 terminal villi. These terminal villi are where the critical exchange of gases and nutrients occurs.
In essence, think of each cotyledon as a tree-like structure originating from a stem villus, with increasingly smaller branches (villi) reaching out to maximize surface area for exchange.
