Inferior vena cava. The inferior vena cava (or IVC) (Latin: vena, vein, cavus, hollow) is a large vein that carries deoxygenated blood from the lower and middle body into the right atrium of the heart. Its walls are rigid and has valves so the blood does not flow down via gravity.
Tight Junctions The tight junction (also referred to as a zonula occludens) is a site where the membranes of two cells come very close together. In fact, the outer leaflets of the membranes of the contacting cells appear to be fused. Tight junctions, as their name implies, act as a barrier so that materials cannot pass between two interacting cells.
Tight junctions often occur in a belt completely encircling the cell. In a sheet of such cells, material cannot pass from one side of the sheet to the other by squeezing between cells. Instead, it must go through a cell, and hence the cell can regulate its passage.