Phenomena

Placental Fluid Dynamics

A man holding a newborn baby.

The placenta, critical as it is to human life and development, is likely the least-studied organ in the body. Reasons for that abound, from the ethics of studying pregnant people to the historical marginalization of female bodies in medical studies. But what little we do know shows that the placenta is quite incredible.

Shaped somewhat like a flattened cake, the placenta contains a tangle of fetal blood vessels — an estimated 550 kilometers’ worth — bathed in maternal blood. The enormous surface area — nearly 13 meters squared — enables the exchange of oxygen, glucose, and urea through diffusion. These exchanges don’t take place in still conditions, though; blood is always flowing through the vessel network. This means that each exchange depends on both the speed of diffusion and the speed of the flow, a relationship that’s captured with the dimensionless Damköhler number.

Illustration of the intertwined blood vessels of the placenta.
Illustration of the intertwined blood vessels of the placenta.

Some exchanges, like carbon monoxide and glucose, are diffusion-limited, meaning that increased blood flow cannot speed up the process (though additional blood vessel surface area could). In contrast, carbon dioxide and urea are flow-limited exchanges. Fascinatingly, oxygen is close to being both diffusion- and flow-limited, suggesting that the organ has optimized for this exchange. Since pregnancy also involves a large increase in maternal blood volume and changes in lung capacity to help provide oxygen, it seems like the pregnant body heavily emphasizes delivering oxygen to the developing fetus. (Image credit: newborn – J. Borba, placenta – iStock/Sakurra; via Physics World; submitted by Kam-Yung Soh)

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.