Figure 1.

Tissue specificity of blood vessels. a. Vascular structure in liver. Hepatic vascular system is composed of central veins, portal veins, hepatic arteries, and sinusoids. the unique feature of liver sinusoidal endothelial cells (LSECs) is fenestration and lack a typical basement membrane, facilitating macromolecular transport. b. Alveolar-capillary barrier. Type 1 epithelial cells (AT2) cover 95% of the internal surface of each alveolus. They share the basement membrane with pulmonary capillary endothelial cells (PCECs), forming a vast gas exchange surface. Type 2 epithelial cells (AT2) are progenitor cells which have an ability to differentiate to AT1 after injury.