This similarity exists because water, ions, and small solutes are continuously exchanged between plasma and interstitial fluids across the walls of capillaries.
Due to this the lack of connective tissue surrounding the parabronchi and adjacent parabronchial lumen, they exchange blood capillaries or avascular epithelial plates.
While hardened concrete appears solid, it is porous, having small capillaries resulting from the evaporation of water beyond that required for the hydration reaction.
Erythrocyte invasion is enhanced when blood flow is slow and the cells are tightly packed: both of these conditions are found in the alveolar capillaries.