Fenestration & Endothelial Transport

Endothelial transport is much different than epithelial transport. It also though has tight junctions. The tight junctions though can be very tight such as in the blood-brain barrier when there’s no movement of fluid, or in capillaries they sometimes have fenestrations, pores, or sometimes even clefts that will allow things to travel through. So, endothelial transport is going to rely less on specific transporters than epithelial transport does. You’re going to utilize things like pressure and osmolality to move various solutes and solvents around. It is primarily a variable associated with the flux of the substance. So you will filter certain things, hydrostatic pressure is highly involved, and osmotic and oncotic pressures. Remember, osmotic pressures have to do with the ion differences and oncotic pressures have to do with protein differences to draw fluid. This is an example of how pressure can move fluid out of a capillary bed. The higher the amount of pressure, the more fluid travels through. Other examples determine about how much the fenestrations are in terms of their width. Some will allow more fluid to travel out and some will allow less. The other issue that we need to think about with endothelium versus epithelium is that we sometimes turn the membranes a little bit differently. The terminology used for the inside surface is the luminal surface rather than the apical membrane. In terms of the outside is termed the basal surface rather than the basolateral membrane. But if you keep those linked together, you’ll be better off and able to think about the differences between epithelial and endothelial surfaces. Let’s look at how fenestrations can be regulated because normally you think of a pore either being open or being closed, but you can modulate this in certain tissues. The lymphatic is a great example...