fluid and blood. If lymph vessels are blocked, proteins build up in the tissue fluid, the osmotic difference between the tissue fluid and blood decreases, the blood cannot reabsorb the water it releases into the tissue, and the tissues become swollen, a condition called edema. Further, it is the lymph capillaries rather than the blood capillaries that absorb most of the fats digested in the intestine.
Closed at one end, as there is no lymph artery system or lymph heart in humans, the lymph capillaries empty the absorbed tissue fluid called lymph into lymph veins which join together to form larger and larger veins. The veins eventually form two large lymph ducts which empty into the blood veins near the heart. Lymph moves through lymph veins in a similar fashion to how blood moves through blood veins: Skeletal muscles squeeze the lymph vessels during body movement which moves the lymph forward. The lymph is prevented from flowing backwards by a system of one-way valves similar to those in blood veins.
Lymph nodes occur periodically along lymph veins and are composed of connective tissue. The nodes contain many phagocytic cells which filter out from the lymph dead tissue cells and invading cells such as bacteria. Materials which cannot be
ingested by phagocytes such as dust are stored in the nodes. The nodes also produce certain white blood cells. Particularly active during infection, the nodes can become swollen and painful.
