**2.2 Pore matrix concept of endothelial barrier**

Flessner [4] has postulated a new concept which says that the large and small pores will be represented as a single entity with the difference in transport characteristics;

#### **Figure 1.**

*(A and B) Distributed concept of normal ultrafiltration barrier. Dextrose diffuses from dialysate into tissue and sets up an osmotic pressure profile (thick curved line).*

*Preservation of Peritoneal Membrane Structure and Function in Peritoneal Dialysis DOI: http://dx.doi.org/10.5772/intechopen.111586*

**Figure 2.** *Pore-matrix concept of endothelial barrier incorporating the luminal glycocalyx [4].*

being a function of the density of intercellular glycoprotein matrix; as in **Figure 2**. This additional layer of glycocalyx alters the microenvironment near the true, sizeselective boundary.

Moreover, albumin concentration below the glycocalyx but above the tight junction is likely much lower than that in the interstitium. This is because the albumin is unable to diffuse against the ultrafiltrate flow through the gap in the glycocalyx. The glycocalyx density is decreased by perfusion of oxidized LDL, adenosine, ischemia reperfusion injury and TNF-α.
