Table 1.

Types of blood vessels in various organs with different permeability

A. Charge barrier [17–23]
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	Retina [2] brain, spinal cord [66] thymus [67]	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)		skin [12, 13] exocrine glands [73] kidney (peritubular) [74] endocrine glands [73, 75, 76] intestinal mucosa [77, 78] lymph node [79, 80]	Determined by diaphragm <6–12 nm [81]
		Fenestrated (open pores without diaphragm)		Kidney (glomerulus) [82, 83]	Determined by glycocalyx <15 nm [2, 19]
Sinusoidal (discontinuous)	Discontinuous basement membrane	Fenestrated (with and/or without diaphragm)		Liver [84–86] spleen [87]	<50–280 nm, largely differ among species <3–5 μm