**4.1 Mechanisms of transport and absorption**

Exogenous miRNAs are selectively packaged into small microvesicles (MVs). MVs are a mixture of microparticles, exosomes, and other vesicular structures found in human plasma [12]. They are shed from epithelial cells under normal or pathological conditions and can enter the circulatory system to be transported. They contain receptors and ligands on the surfaces of the cells of origin, giving them the ability to interact with target cells and mediate intercellular communication. Exogenous miRNAs take advantage of this ability to regulate host cell gene expression. MVs serve as stable signaling molecules, they protect exogenous miRNAs against serum RNAases and facilitate their transport to target genes [12, 32–34]. They are classified according to their origin, size, and formulation mechanism: exosomes, microvesicles, and apoptotic bodies [35].
