Lymph nodes are pea-shaped patches of lymphatic tissue strategically placed throughout the body to filter lymph as it flows through the lymphatic vessels.
Lymph nodes tend to appear in clusters and are comprised of masses of lymphocytes and macrophages, defensive cells concerned with immunity and protecting the body against disease.
Lymph nodes are often referred to as glands because, when they swell, they are referred to as swollen glands, which are often accompanied by an infection.
Lymph nodes are found beneath the epithelia lining various organs of the respiratory, digestive, and urinary systems. All of these systems have access to the outside world and, therefore, have a route of entry into the body of possible harmful organisms and toxins.
Size ranges from that of a pinhead to 2.5 cm (1 inch). The increase or decrease depends on the number of lymphocytes present at any given moment. In large lymph nodes, there is often a central region, called a germinal center, where lymphocytes are actively dividing.
As lymph passes through the lymph nodes, 99% of the antigens are removed. As the antigens are detected, T cells and B cells are stimulated and an immune response is initiated.
Lymph nodules can refer to two different things. Each node has several compartments called nodules which are separated by sinuses or spaces filled with lymph. In addition, the smallest of the lymph nodes are often called nodules. Some of these nodules have specific names. For instance, those in the small intestine are called Peyer’s patches, while those in the pharynx are called tonsils.
Types of lymph nodes
- Axillary lymph nodes are located in the armpit or axillary region. These nodes drain and cleanse lymph coming from the upper extremities of the shoulder and breast areas. Cancer cells that escape from the breast are often trapped in the axillary lymph nodes.
- Cervical lymph nodes drain and cleanse lymph coming from the head and neck areas. Enlarged and tender cervical lymph nodes often accompany upper respiratory infections.
- Inguinal lymph nodes are located in the groin area. These nodes drain and cleanse lymph from the lower extremities and from the external genitalia. When they become enlarged, they are often referred to as buboes, as in the case of bubonic plague.
- Mesenteric nodes are found between the two layers of peritoneum (membrane) that form the mesentery. The mesentery is the membranous fold that attaches such organs as the small intestine to the body wall. There are some 100 to 150 of these nodes.
- Tracheobronchial nodes are found near the trachea and around the larger bronchial tubes. For those living in highly polluted areas, these nodes become so filled with carbon particles that they become solid black masses, resembling lumps of coal. Lymphadenopathy is a chronic swelling or excessive enlargement of a lymph node. It may occur in response to:
- bacterial infections
- viral infections
- endocrine disorders
Since the lymphatic capillaries offer little resistance to the passage of cancer cells, these cells travel on through the lymphatic vessels to become trapped in the lymph nodes.
Lymphomas are an important group of lymphatic system cancers.