Where do gaseous and chemical exchanges between blood and interstitial fluid take place?

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Gaseous and chemical exchanges between blood and interstitial fluid occur across capillary walls. These walls are extremely thin—just a single layer of endothelial cells with a basement membrane—so they place the plasma in very close contact with the surrounding interstitial fluid, allowing oxygen, carbon dioxide, nutrients, wastes, and other small solutes to diffuse readily. The capillary network also provides a large surface area, and its various permeability features (intercellular clefts, fenestrations, or transcellular transport in some tissues) tailor how easily substances move between blood and interstitial fluid. Lymphatic vessels transport interstitial fluid away rather than serving as the primary exchange surface with blood; venous sinuses are specialized vessels in certain organs, not the typical site of routine exchange; arterioles feed the capillary beds but the actual exchange happens across the capillary walls.