Lymphatic system

The lymphatic system is part of the circulatory system and has two jobs at once: taking part in the body's defense and draining the excess extracellular fluid, that is, the fluid that sits between the cells.

That fluid enters through the lymphatic capillaries, the finest tubes in the network. The cells that form their tips overlap one on top of another, and they pull apart only when the pressure of the interstitial fluid, the fluid outside, exceeds the pressure inside the capillary. The edges of the capillary overlap like a swinging door and open only when something pushes from outside. When they open, in come lymphocytes, which are defense cells, along with fluid, bacteria, cell debris and plasma proteins.

From there, lymph follows an orderly path. The afferent vessels, the ones heading into the node, carry it unfiltered; the efferent vessels, the ones leaving, carry it out already filtered. They all converge and ultimately end in two large ducts: the right lymphatic duct and the thoracic duct.