What is the most important factor in determining what crosses the "placental barrier"?

Question

Quizplus · Accepted Answer

The most important factor in determining what crosses the placental barrier is the size of a molecule. The placental barrier is made up of the placental membrane, which only allows certain substances to pass through based on their size, charge, and lipid solubility. Small molecules such as oxygen, carbon dioxide, and some hormones can pass freely through the placental barrier, while larger molecules such as proteins are generally unable to cross.

What Is the Most Important Factor in Determining What Crosses