Lymphoid

The lymphatic system is part of the circulatory system, comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph (from Latin lympha "water goddess") unidirectionally towards the heart. The lymphatic system was first described in the seventeenth century independently by Olaus Rudbeck and Thomas Bartholin. The lymph system is not a closed system. The circulatory system processes an average of 20 liters of blood per day through capillary filtration which removes plasma while leaving the blood cells. Roughly 17 liters of the filtered plasma actually get reabsorbed directly into the blood vessels, while the remaining 3 liters are left behind in the interstitial fluid. The primary function of the lymph system is to provide an accessory route for these excess 3 liters per day to get returned to the blood. Lymph is essentially recycled blood plasma.