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Physiology of Breast Cancer Lymphedema The lymphatic system, along with the system of blood vessels, plays an important role in maintaining the fluid balance of the tissue. These systems maintain fluid balance (and therefore prevent chronic edema) by facilitating a dynamic equilibrium between the tissue and the vasculature by shuttling proteins and fluids into and out of the tissue. Remember, to swell is normal but to stay swollen is not. We all have swelled at some time, whether it be because of a hot, humid day or a salty meal. But, once the swelling occurs, our tissue fluids will work to balance themselves out, and the swelling will resolve. This is what we mean by "dynamic equilibrium." The blood vessels which assist in this equilibrium consist of the arterioles and post-capillary venules. An arteriole carries blood and its nutrients, including oxygen and protein, into the tissue. Approximately 90% of the fluid that enters the tissue is returned to the heart via the venous system. In addition, the venous system is responsible for returning most of the smaller unused proteins back to the blood system. The remaining 10% of the fluid, along with larger proteins is returned to the blood system visa the lymphatic system. Therefore, arterial inflow is balanced by venous and lymphatic outflow (schematic A) Protein molecules transport oxygen and other nutrients to the cells of the tissues. The excess protein must be removed from the tissue via the venous and lymphatic systems. Protein has a tendency to attract water and edema will occur if it is allowed to accumulate in the tissues of the body. The utilization of protein as food by cells, the transport of the unused proteins from the tissue and the removal of excess fluid via the venous and lymphatic systems are most critical in maintaining fluid balance and in the prevention of edema formation.
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