8.2.2　Lymphatic drainage and blood circulation of ...

Blood vessels and lymphatic vessels in the skin are the histological structure foundation for ensuring the systematic effect of transdermal administration.Blood vessels are distributed in the dermis and subcutaneous tissues，and the capillaries are particularly abundant around the skin appendages，which provide favorable conditions for macromolecular drugs and nano-drugs entering the systemic circulation through the transcellular pathway.The skin capillary lymphatic vessels originate from the dermal papilla layer with high permeability.After penetrating into the skin，drugs can be drained into the lymph nodes along with the skin tissue fluid through the skin capillary lymphatic vessels.Besides，drugs can also act on cells in the skin，and indirectly produce systemic effects through cell migration.For example，the vaccine can work on antigen-presenting cells in the skin，such as Langerhans cells in the epidermis and dendritic cells in the dermis，which can further migrate to the lymph nodes，thereby producing a systemic immune effect.(https://www.daowen.com)