Here's why:
* Capillaries are the smallest blood vessels. They have thin walls made of a single layer of epithelial cells (endothelium), which allows for easy diffusion of substances.
* Interstitial fluid is the fluid that surrounds cells. It's essentially a "middleman" between blood and cells, allowing for the transport of nutrients, oxygen, and waste products.
The process of exchange:
1. Blood flows through the capillaries.
2. Nutrients and oxygen from the blood diffuse across the capillary walls into the interstitial fluid.
3. Waste products and carbon dioxide from the interstitial fluid diffuse across the capillary walls into the blood.
This exchange is driven by differences in concentration gradients and pressure.
