What are the characteristics of capillary walls?

Capillary walls are thin, semi-permeable, and composed of a single layer of endothelial cells.

Capillaries are the smallest blood vessels in the body, with walls that are only one cell thick. This thinness is crucial for their function, as it allows for the efficient exchange of oxygen, nutrients, and waste materials between the blood and the body's tissues. The walls are composed of endothelial cells, which are flat, thin cells that line the interior surface of blood vessels.

The capillary walls are semi-permeable, meaning they allow certain substances to pass through while blocking others. This selective permeability is essential for maintaining the balance of substances in the body. Oxygen and nutrients in the blood can pass through the capillary walls to reach the body's cells, while waste products from the cells can enter the capillaries to be carried away for disposal.

The structure of capillary walls also includes a basement membrane, a thin layer of extracellular matrix that provides support and anchorage for the endothelial cells. This membrane is permeable to water and small solutes, but not to larger molecules and cells, helping to regulate the movement of substances in and out of the capillaries.

In addition, some capillaries have tiny openings or pores in their walls, known as fenestrations. These fenestrations allow for the rapid exchange of larger molecules, such as proteins, between the blood and the surrounding tissues. However, the presence and size of these fenestrations can vary depending on the specific location and function of the capillaries.

Overall, the characteristics of capillary walls - their thinness, semi-permeability, and composition of endothelial cells - are all key to their role in the transport and exchange of substances within the body.