Lymph
Normally there is very little net egress of fluid as blood flows through capillaries. Recall that the capillaries are relatively impermeable to plasma proteins, and these generate an effective osmotic force to retain fluid within the vessels.
However, there is a relatively small net loss of both protein and fluid from capillaries. These are normally taken up by a system of small lymphatic vessels, and the resultant fluid is lymph.Lymphatic vessels begin as blind-ending vessels similar in structure to capillaries, and these join to form larger vessels resembling veins. The direction of lymph flow is from small lymphatics to large ones. The largest of the lymphatic vessels join with large veins just cranial to the heart, and here all lymph returns to the blood. Edema is an abnormal accumulation of fluid within the interstitial space. Blockage of lymphatic vessels can produce edema within the area normally drained by those lymphatics.
Lymph is a clear, colorless liquid somewhat similar to blood plasma, from which it is derived. Lymph usually contains numerous lymphocytes, inorganic salts, glucose, proteins, and other nitrogenous substances. Neutrophilic leukocytes are not normally present in great numbers except during acute infections.
Lymph derived from the intestine during digestion may contain large quantities of lipids, giving it a milky appearance. This milky lymph, called chyle, results from the absorption of lipids into the lacteals, the small lymphatics of the intestine.