The protein
molecules are too large to be re-absorbed by venules (smallest veins)
and in a healthy lymphatic system, this protein-rich fluid is removed by
lymphatic vessels and circulated through the lymphatic system, filtered
by lymph nodes and eventually the lymph fluid returns to the
circulatory system. However, a compromised lymphatic system may be
unable to collect this fluid sitting in the tissue. Protein attracts
water, so the longer it takes for the lymphatic system to "pump out"
this protein rich fluid, the more fluid is attracted to the protein and
more swelling occurs.
This is why diuretics are not helpful with
lymphedema. The diuretics remove some of the fluid, but do nothing to
move the protein out of the tissue.