Lymphatic System, Lymphatic Vessels

Lymphatic system, lymphatic vessels

Along with the system of blood vessels in the body, there is a similar independent group of vessels that form the lymphatic system. Lymph moves through these vessels - a transparent, colorless liquid, which, like tissue fluid, originates from blood and is very similar to blood. It contains much less protein than blood (since protein molecules are large and diffuse slowly) and lacks red blood cells.

But it contains leukocytes, some of which enter the lymphatic capillaries from the tissue fluid, and some are formed in the lymph nodes. In other respects, lymph is similar to blood. The lymphatic system differs from the circulatory system in that its vessels serve only to return fluid to the heart.

There are no arteries in this system, but only capillaries and veins distributed throughout the body. Capillaries are extremely thin, their walls consist of only one layer of cells. They resemble blood capillaries, but are closed at one end.

Lymph diffuses into these capillaries from the surrounding tissue fluid. At the other end, the capillaries communicate with the lymphatic veins, which, like the veins of the circulatory system, are equipped with valves and have thin walls. These veins, merging, form successively larger veins, the largest of which flows into the left brachial vein of the circulatory system.

It is important to remember that fluids reach the cells of the body in only one way - through the arteries, arterioles and capillaries of the circulatory system, while there are two return paths - through the blood capillaries and veins and through the lymphatic capillaries and veins.

At the confluence of lymphatic vessels are clusters of cells called lymph nodes, which produce lymphocytes and filter out dust particles and bacteria to prevent them from entering the bloodstream. The ducts through which lymph passes through these nodes are so narrow and tortuous that it flows very slowly and bacteria penetrating with it can be detained and phagocytosed by leukocytes.

Some bacteria sometimes pass through the first lymph node and linger in the second or third; with a massive infection, bacteria can penetrate all nodes and invade the bloodstream. But even in these cases, the lymph nodes are useful, since they slow down the spread of infection and give the body time to accumulate white blood cells and mobilize them to fight it.

When microbes enter the lymph nodes, the latter become swollen and painful; for example, with tonsillitis, the cervical nodes visibly swell. In residents of large cities and people who smoke a lot, the lymph nodes in the lung area become filled with dust and soot particles and become dark gray or black. These particles can eventually impair the functioning of lymph nodes and reduce resistance to lung diseases such as tuberculosis.

Movement of lymph. The frog has four lymphatic “hearts” that pulsate and push lymph through the vessels. They are simply sections of lymphatic vessels that have thickened walls, without any chambers or valves. In humans, unlike frogs, the movement of lymph is ensured by contraction of nearby skeletal muscles, compressing the lymphatic vessels (valves prevent reverse flow), and by respiratory movements of the chest.

The outflow of lymph from the intestines is facilitated by spasmodic contraction and relaxation of intestinal villi - finger-like projections protruding from the walls of the intestine into its lumen. Lymph flows much slower than blood.

Functions of the lymphatic system. The lymphatic system has four functions. First, it helps return tissue fluids to the circulatory system. Since under normal conditions the walls of blood capillaries are slightly permeable to plasma proteins, these proteins