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.
Gap junction: An organized collections of protein channels in cell membranes that allows ions and small molecules to pass between adjacent cells. The protein channels that make up gap junctions consist of two connexons. One connexon resides in the membrane of one cell. It aligns and joins the connexon of the neighboring cell, forming a continuous aqueous pathway by which ions and small molecules can freely pass (passively) from one cell to the other.