Lymphatic System – An Overview of the Structure and Function of Lymph and the Lymphatic System

The word “lymph” comes from the Latin “lympha,” which means “clear water.” In fact, lymph is a watery, yellowish substance. It flows through the entire body via meter-long, extremely fine channels.

Lymph is formed from nutrient-rich blood plasma. As blood passes from the arteries into the veins, about 10 percent of the blood plasma remains in the spaces between cells. That amounts to about two liters per day. This residual fluid is called interstitial fluid.

A Parallel Network: The Lymphatic Vessels

Extremely thin lymph capillaries originate throughout the interstitial spaces of the body. They absorb the interstitial fluid remaining there and transport it as lymph toward the heart. There, it is recombined with the blood in the superior vena cava.

The lymph capillaries, which are initially highly branched, merge to form larger lymphatic vessels. These usually run parallel to the venous blood vessels. Parts of these vessels, known as lymphatic hearts, contract about ten times per minute due to muscle contractions. In this way, they provide the necessary pumping action.

The lymphatic system extends throughout the entire body. A lymph node is also shown here © lom123 | AdobeStock

The Lymph Nodes

At certain locations, for example,

• under the armpit,
• on the neck, and
• in the groin,

the lymphatic vessels are interrupted by nodes. Here, the lymph is filtered to remove

• pathogens,
• cell debris, and
• foreign bodies

to protect the body from harm.

Lymph nodes, which are about 1–20 mm in size, are part of the lymphatic system. They contain lymphocytes and macrophages—specialized immune cells that are a type of white blood cell and recognize and attack viruses and bacteria.

The lymph nodes in the neck may become palpable during a viral flu, for example. This is because they increase their activity in response to the infection and swell accordingly.

Lymphatic capillaries (green) embedded between blood vessels © ilusmedical | AdobeStock

In addition to the lymph nodes, the system includes other lymphatic organs. Lymphocytes can multiply or differentiate within these organs. Their functions complement one another:

The Bone Marrow

This is where it all begins. In the bone marrow, a process called lymphopoiesis takes place, in which lymphocyte stem cells first develop into lymphoblasts. From these, in turn, two types of lymphocyte precursors emerge:

• pro-T lymphocytes and
• pro-B lymphocytes.

They pass through the bone marrow and then settle in the various other lymphoid organs.

The Thymus

In the thymus, the pro-T lymphocytes coming from the bone marrow are converted into T lymphocytes. They first undergo a selection process and then maturation, which prepares them for their important role in the immune system.

The Spleen

Among other things, the spleen produces the aforementioned macrophages (also known as defense cells or phagocytes). In addition, it stores lymphocytes and breaks down aged blood cells.

The Tonsils or Lymphatic Ring

The lymphatic ring consists of the pharyngeal, lingual, and palatine tonsils. It destroys pathogens that attempt to spread into the body via the air we breathe and through the mucous membranes. B lymphocytes also multiply in the tonsils.

Peyer’s patches are also called Peyer’s plates or Peyer’s glands. They are found in the mucous membrane of the small intestine all the way to the appendix.

They consist of a collection of microscopic colonies of B lymphocytes, known as lymphoid follicles. They play an important role in defending against infections in the intestine and relay immunological information.

A Summary of the Lymphatic System’s Functions

1. It is an important part of the immune system.
2. It regulates fluid volume in the tissues.
3. It transports dietary fats from the abdominal cavity directly to the cells.

If lymph flow is disrupted or interrupted, fluid accumulates in the tissues. Lymphedema most commonly occurs in the extremities.

The affected area of the body swells, and the subcutaneous fatty tissue takes on a doughy consistency. If left untreated, this can lead to

• circulatory disorders and
• nerve damage

with corresponding functional impairment. The only effective remedy is regular manual lymphatic drainage. During this procedure, a massage therapist stimulates the vascular system with gentle, circular movements. This allows the lymph to drain more effectively.

Inflammation of lymphatic vessels usually occurs in one of the superficial lymphatic pathways. The skin in the affected area becomes red, and a red streak spreads from the site of inflammation toward the center of the body. The area is usually painful and slightly swollen.

If lymphangitis is caused by bacteria, it responds well to treatment with antibiotics. See a doctor promptly! Otherwise, complications may arise, and in the worst-case scenario, it could even lead to blood poisoning (sepsis).

Hodgkin’s Lymphoma and Other Cancers

In addition to viruses and bacteria, lymph nodes also filter out tumor cells in cases of cancer. These cells accumulate in the nodes and then gradually spread throughout the body via the lymphatic system.

To prevent this, a doctor may remove individual lymph nodes located near a tumor.

Other cancers, such as

• lymphocytic leukemia (acute: ALL or chronic: CLL) or
• Hodgkin’s lymphoma (Hodgkin’s disease)

directly affect the lymphatic system. In malignant lymphomas, the lymph nodes typically swell. They occur in various forms and respond to treatment to varying degrees.

In breast cancer, the lymph nodes in the armpits swell (so-called sentinel lymph nodes) © Henrie | AdobeStock

The lymphatic system is a central part of the immune system and performs vital functions throughout the body. Its structure and function demonstrate that both primary and secondary lymphatic organs work closely together to produce and activate immune cells. These lymphatic organs include structures such as bone marrow and the thymus (primary) as well as lymph nodes and the spleen (secondary), which serve as important filtering stations.

Through lymph flow, tissue fluid, proteins, cells, and cellular debris are continuously removed and ultimately transported via the thoracic duct into the superior vena cava and thus into the bloodstream. The lymphatic system ensures that excess fluid is removed from body tissues and purified. Lymphatic vessels permeate the entire body and are closely connected to the venous system as well as blood vessels and arteries. In addition to drainage, the functions of the lymphatic system also include defending against pathogens such as viruses and bacteria. Specialized immune cells, such as B lymphocytes and T lymphocytes, play a central role in the immune system. Lymphocyte proliferation occurs in the secondary lymphoid organs, enabling an effective immune response.

The lymphatic system transports substances from the lymph and ensures that lymphatic substances and fluid are transported from the tissues via initial lymphatic vessels and larger lymphatic vessels. The lymph fluid is distributed throughout the body via capillaries and larger structures and is subsequently released into the venous plexus. In total, several liters of lymph fluid are moved through this system every day.

Disorders of the lymphatic system, such as lymphedema, demonstrate how important proper drainage is. When fluid is no longer adequately drained, it accumulates in the tissues. Nevertheless, a healthy lymphatic system ensures that all vital functions remain stable and that the body is effectively protected.

What is the lymphatic system?

The lymphatic system is part of the immune system and consists of lymphatic vessels, lymph nodes, and lymphatic organs. Lymph, a fluid, is transported through the lymphatic vessel system and distributed throughout the body. In the process, pathogens, cellular debris, and excess fluid are removed from the tissues and ultimately returned to the bloodstream.

Which organs are part of the lymphatic system?

Lymphatic organs include primary and secondary lymphatic organs. Primary organs are the bone marrow and thymus, where immune cells are formed and mature. Secondary lymphatic organs, such as lymph nodes and the spleen, serve as filtering stations where lymphocytes are activated. Peyer’s patches in the small intestine are also part of these structures.

What is the function of lymph?

Lymph is a clear fluid derived from interstitial fluid. It transports proteins, immune cells, and metabolic waste products through the lymphatic vessels. In the process, it is filtered and purified in the lymph nodes. It then flows into the superior vena cava via larger lymphatic vessels such as the thoracic duct.

How does lymph flow work?

Lymph flow begins in the lymphatic capillaries, which absorb fluid from the tissues. From there, the lymph fluid travels through larger lymphatic vessels and lymphatic pathways. Muscle movement and pressure gradients propel the lymph forward until it finally re-enters the venous system at the venous angle.

What are common disorders of the lymphatic system?

Among the most common disorders of the lymphatic system are lymphedemas, in which fluid accumulates in the tissues. Infections, viruses, or other causes can also affect the lymphatic system. In such cases, swelling occurs because the lymphatic vessels cannot adequately drain the excess fluid.