Hematologic & Lymphatic Overview (38 CFR 4.117)

The hematologic and lymphatic systems are distinct entities; however, because a common origin of their cells is shared in the bone marrow, and the movement of components of the lymphatic system is affected by the hematologic system, these areas are considered together. Both systems are parts of the vascular system.

The major components of the hematologic system are the blood and the bone marrow. The blood is the fluid tissue, which circulates through the heart, arteries, veins, and capillaries, and the bone marrow is the site for the manufacture of new blood cells. Blood consists of a variety of blood cells freely moving in a fluid called plasma. Functions of the blood include: maintenance of normal body temperature and body chemical balance; transportation of chemical messengers such as hormones, gases, nutrients, immune cells and blood cells; and protection against infection and blood loss through the clotting factor. The functions of the blood are performed by different blood cells in the plasma. The blood cells include: erythrocytes; leukocytes; and thrombocytes. There are two types of leukocytes. One type of leukocytes includes neutrophils, eosinophils and basophils, and the second type is termed monocytes.

The lymphatic system is a circulatory system that includes lymphatic vessels that collect lymph fluid throughout the body and return it to the blood. Additional components of the system are organs composed of lymphatic tissue such as lymph nodes and lymphoid organs such as the spleen, bone marrow, the thymus, adenoids and tonsils. Lymphocytes and monocytes produced by these organs provide a defense against disease-producing organisms and provide immunity.

Hematologic and Lymphatic System