Lymph circulation: physiology, pharmacology, and biomechanics

Lymph is the fluid in the lymphatic system. The lymphatic system, a complex network of vessels, is essentially a drainage system within the body which transports excess fluid and metabolic waste products from interstitial spaces into the blood circulatory system. Lymph flow is governed by extrinsic forces due to the movements of organs and skeletal muscles which exert external pressure on the lymphatic walls, and by the intrinsic forces due to rhythmic contractions of smooth muscle in the walls of the lymphatic vessels which play a major role in lymph circulation. Intensities of these lymphatic smooth-muscle contractions are modulated by several humoral mediators such as epinephrine, serotonin, and PGE1. These notions of lymphology, together with principles of mechanics, have been integrated into mathematical models of lymph circulation. Model analysis has revealed several interesting features of lymph circulation and lymphatic system design. Distention-induced enhancement of contractility is important in achieving significant increase in lymph flow during edema.