LITMIR.BIZ

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which removes unwanted material from the blood, especially defective red blood cells. Before birth, red blood cells are formed here, and in the normal adult the spleen serves as a reservoir for blood. If it is surgically removed, the body loses some of its ability to produce protective antibodies and to extract unwanted substances from the blood, thus lessening one’s ability to fight infection. However, other organs, especially the liver, will compensate for this loss and take up the infection-fighting job.

      One of the largest organs in the body, the liver is also one of the most important. Similar to a chemical processing plant, it performs a variety of vital functions: production of cholesterol and bile; manufacturing of proteins; storage of iron, glycogen, and vitamins; removal of poisons and waste products from the blood; and conversion of waste to urea. It is also a main component of the digestive system, though it lies outside of the digestive tract. Because it filters and destroys bacteria and helps detoxify the body, some texts (for example, The Merck Manual) list it as part of the lymphatic system as well. Located in the upper right section of the abdomen behind the lower ribs, it is dark red in color and one of the most versatile organs in our body.

      The appendix, also called vermiform appendix, is a small, finger-shaped, wormlike tube that projects from the ascending colon (on the right side of the abdomen) of the large intestine at its junction with the small intestine. Because it is chiefly lymphatic tissue, an infection anywhere in the body that also produces enlarged lymph nodes can increase its glandular tissue, eventually causing inflammation and infection. Unless the body’s defenses overcome the infection, the appendix may have to be removed before it ruptures, leading to peritonitis, a serious and dangerous condition. Sometimes considered a rather useless structure, it is often routinely removed by surgery because of its potential for this painful and serious inflammation.

      Red blood cells, white blood cells, and platelets are produced in the bone marrow, which is the innermost portion of the bone and shaped like a hollow cavity. In response to infection, the bone marrow produces and releases more white blood cells, the body’s major mechanism for fighting infections. When blood cells for some reason show abnormalities, a bone marrow examination is often used to determine the cause. Disorders of bone marrow include diseases in which either too many or too few blood cells are produced.

      From this brief overview of the main components of the lymphatic system, we may get a sense of the important role it plays in our body’s overall health and well-being. Just the extent and pervasiveness of this system, affecting a wide range of tissues, organs, and vessels, may give us a clue to the necessity of caring for it and keeping it working in an optimal fashion.

      Here follow a few more points regarding the composition of the lymphatic system:

      Analogous to the tree trunk, mentioned earlier as a visual description, are two large, main lymphatic vessels: the thoracic duct and the right lymphatic duct (the latter actually comprises three collecting ducts). These structures, located roughly in the center of the thorax, are the principal channels through which lymph passes into the venous blood. (See Fig. 1.) They serve as receivers of the lymph from the whole body: lymph from the body’s upper right quadrant drains into the right lymphatic duct (and then into the right subclavian vein), while lymph from the rest of the body drains into the thoracic duct (and then into the left subclavian vein). (See Fig. 3.) As their names indicate, the subclavian veins are located underneath the right and left clavicles (collar-bones) in the upper chest area. Thus, the important function of lymphatic vessels is now fulfilled: to return “leaked” plasma proteins and fluid, arising from the spaces between the cells and flowing through the lymphatics, and finally deposit them in the bloodstream.

      Schematically, the flow of fluid, then, may be represented in this manner (the words in parentheses give the name of the fluid in those vessels): arteries (blood plasma)

blood capillaries interstitial spaces (interstitial fluid) lymphatic capillaries (lymph) lymphatic vessels lymph nodes lymphatic trunks lymphatic ducts subclavian veins (blood plasma). This “flow chart” represents the origins of the fluid: one that “leaks” from or seeps out of the blood (arteries) plus the fluid that fills the spaces between the cells (interstitial fluid). This excess fluid, about three liters per day, is collected and drains, then, into lymphatic capillaries, where it becomes lymph; it ultimately enters into the venous blood through the subclavian veins. In truth, the lymphatic system is a second circulatory system, carrying lymph instead of blood, and traveling through various lymphatic vessels, which resemble capillaries and veins, on its way back to the heart. Its chief function is to help drain the excess fluid from the interstitial area and to pick up proteins that may have leaked out of the capillaries.

       ORIGIN AND HISTORY OF LYMPH

      We exist within our bodies in a wet world, water comprising 70-80 percent of our being. Flowing between all the cells, interstitial fluid bathes these cells with life-giving substances. Its clear, colorless liquid carries such microscopic particles as white blood cells, proteins, and other substances vital to the life of the cell. Blood capillaries also exude fluid into tissues, but not all this fluid returns to the blood, thus creating an accumulation, or excess, of tissue fluid. Collecting this excess fluid from between the cells and eventually returning it to the body’s circulation is the purpose for this vast lymphatic network, with its miles of tubes and channels of interconnected vessels. When too much of the interstitial fluid accumulates, the lymphatic vessels, as stated previously, channel it through a series of closed-end tubules. Now it is called lymph, a word derived from the Latin lympha, meaning “clear water” or “spring water.”

      Figure 3

      Drainage of lymphatic fluid

      Figure 4

      Lymphatic capillaries and vessel wall musculature.

      According to Webster’s New World Dictionary (3rd college edition), the word lymph is also influenced etymologically by the Greek nymphē, our English word nymph. In Roman and Greek mythology, nymphs were a group of minor nature goddesses, usually represented as young and beautiful, who inhabited rivers, springs, seas, or lakes: that is, places of clear water. The word limpid, with similar origin, means “perfectly clear; transparent; not cloudy or turbid.”

      Owing to its transparent quality, lymph is difficult to see during dissections, so its discovery as part of an integrated system in the body developed slowly over time and arrived late on the medical scene.

      Some ancient civilizations—such as China, India, and Egypt—had elementary notions of a “white blood,” possibly referring to the milky, intestinal lymph fluid that follows digestion of a fatty meal. Traditional Chinese medicine speaks of a water element connected with the bladder and kidney meridians; it differentiated between liquids of the body and blood. Ancient India’s Ayurvedic medicine had knowledge of “interstitial liquid,”

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