Glycocalyx layer | Anionic mesh-like layer with regular spacing of <20 nm for continuous and fenestrated vessels (irregularly found on sinusoidal vessels), on both the surface of IEJ clefts and endothelial cells. | ||||
B. Size barrier (reviewed in [2]) | |||||
Types of blood vessels | Types of endothelial cells | Interendothelial junctions (IEJs) | Representative organs | Estimated upper limit for paracellular transportation [4] | |
Continuous(non-fenestrated) | Continuous basement membrane | No fenestrae | Tight junctions and adherens junctions | Determined by IEJs (TJs) <1 nm | |
Adherens junctions with limited contribution of tight junctions | skin [12, 13] muscle, heart [68, 69] adipose tissue [70] lung [71, 72] | Determined by IEJs (AJs) <5 nm | |||
Fenestrated | Fenestrated (with diaphragm) | exocrine glands [73] kidney (peritubular) [74] | Determined by diaphragm <6–12 nm [81] | ||
Fenestrated (open pores without diaphragm) | Determined by glycocalyx | ||||
Sinusoidal (discontinuous) | Discontinuous basement membrane | Fenestrated (with and/or without diaphragm) | spleen [87] | <50–280 nm, largely differ among species <3–5 μm |