Does it have structure in it, or is it more like a smooth flat, plate?

它有结构吗，还是更像一个光滑的平板？

Capillaries have walls that are only one epithelial cell thick. The capillary walls are transparent and are made of smooth plate like cells that continue from the lining of the arteries.

毛细血管壁极薄，故氧及营养物质能从血流离开，进入（胞外）组织液。