Clinical Overview of the Lymphatic System - dummies

Clinical Overview of the Lymphatic System

By David Terfera, Shereen Jegtvig

The lymphatic system includes a system of lymphatic capillaries, vessels, nodes, and ducts that collects and transports lymph, which is a clear to slightly yellowish fluid, similar to the plasma in blood. The lymphatic system is important for maintaining your body’s fluid balance, and it helps transport some fats. It also works along with the rest of the immune system (namely, the leukocytes) to fight infections.

The lymphatic system is really a one-way street; lymph doesn’t circulate the way blood does through both veins and arteries.

Lymphatic plexuses (networks) are made up of tiny lymphatic capillaries, which are located in most of the tissues of the body. The capillaries collect extra cellular fluid (lymph) from the tissues. The lymph comes from blood plasma that leaks out of small blood vessels called capillaries. The lymph enters into small tubes called lymphatic vessels, which come together to form larger and longer lymphatic vessels as they carry the lymph away from the tissues and return it to the blood at the subclavian veins.

Lymphatic vessels are both superficial and deep. The superficial vessels start in the tissue just below the skin and drain into the deep vessels that usually run alongside the blood vessels.

Special lymphatic capillaries called lacteals receive fat that has been absorbed from the small intestine. The fat is transported to the lymphatic ducts and then to the venous system.

Lymphatic vessels that carry lymph toward a lymph node are called afferent lymphatic vessels. The ones that carry lymph away from lymph nodes are called efferent lymphatic vessels.

Lymphatic vessels are similar to veins, but they have a bumpier appearance due to a large number of valves found in the vessels. The valves keep lymph from flowing backward.

Lymphatic vessels are found in most of the organs and tissues of the body, but they’re not found in the eyeball, the epidermis (outer layer of the skin), the cartilage, or the bone marrow. The central nervous system has no lymphatic vessels, either — extra fluid drains into the cerebral spinal fluid. In addition to being present in the lymph nodes, lymphatic tissue is also found in a few additional spaces of your body. The lymphoid organs assist the lymphatic system. They include the thymus, spleen, tonsils, and appendix, along with some special tissue in the gut.

Filtering lymph through nodes

Different lymphatic vessels carry lymph to small, bean-shaped masses of lymphatic tissue called lymph nodes. They’re found mostly around the neck, armpits, groin, thorax, knees, and elbows, and their function is to filter and monitor the lymph for foreign particles such as pathogens (bacterial and viruses) and cancerous cells before it returns to the blood. As the lymph enters the node, it flows through spaces called sinuses on its way toward the efferent vessels. The cortex houses the lymphocytes that participate in the monitoring of the lymph.


After the lymph is filtered, it leaves the lymph node via an efferent lymphatic vessel, traveling toward even larger vessels called lymphatic trunks that are formed by the confluence of lymphatic vessels. It finally travels to the lymphatic ducts.

Collecting lymph in ducts

The lymphatic ducts are the final step along the lymphatic pathway. From there, the lymph joins the blood in the venous system. Here are the major lymphatic ducts you should know:

  • Right lymphatic duct: This duct drains lymph from the upper-right side of the body, including the right sides of the head, neck, and thorax and the entire right upper extremity. It ends at the right subclavian vein at the junction of the right internal jugular vein.

  • Thoracic duct: This duct receives lymph from the rest of the body. It starts off in the abdomen as a sack called the cisterna chyli and runs upward through the thorax and enters the left subclavian vein at the junction of the left internal jugular vein.

Lymphedema is a disorder where lymph accumulates in the tissues because it isn’t removed properly by the lymphatic system. The accumulation causes swelling and can occur when part of the lymphatic system is damaged or blocked. Lymphedema can be caused by infections, cancer, surgical removal of lymph nodes, damage of lymph nodes due to radiation therapy, or certain inherited conditions.