Numerous lymph nodes are located within the armpit, an area known as the axilla. These small, bean-shaped organs are a fundamental part of the lymphatic system, which is a major component of the body’s immune defense network.
Anatomy: Where the Axillary Nodes Are Located
The armpit contains a collection of approximately 20 to 40 lymph nodes embedded within the fatty tissue of the axillary space. These nodes are organized into five distinct groups based on their anatomical position and drainage pattern. This network is collectively known as the axillary lymph nodes.
These five groups are the lateral (brachial), anterior (pectoral), posterior (subscapular), central, and apical nodes. The lateral group primarily handles drainage from the upper limb, while the anterior group collects lymph from the chest wall and breast tissue. Lymphatic fluid collects in these groups and flows toward the apical nodes, which serve as the final common pathway before returning to the circulatory system.
This network acts as a drainage basin for a vast region of the upper body. The axillary nodes filter fluid originating from the entire upper limb, the majority of the breast, the chest wall, and the upper part of the back and abdomen.
Essential Role in Immune Defense
The main function of a lymph node is to filter lymphatic fluid, or lymph, which circulates throughout the body. Lymph is a clear fluid that leaks out of the bloodstream to bathe tissues, collecting waste products and foreign materials. The axillary nodes intercept this fluid from the upper body region.
As lymph flows through the nodes, specialized immune cells, including lymphocytes and macrophages, inspect the fluid for signs of trouble. These immune cells are ready to trap and destroy foreign invaders like bacteria, viruses, and other abnormal cells. When a threat is detected, the immune cells within the node begin to multiply rapidly to mount a targeted response.
This cellular reproduction is a localized preparation for attacking the detected pathogen. Once activated, these immune cells are released back into the lymphatic and circulatory systems to patrol the body and neutralize the threat.
Common Reasons for Swelling and Tenderness
Swelling in the axillary lymph nodes is a sign that the nodes are actively engaged in fighting an infection. The rapid multiplication of immune cells causes the node to enlarge, sometimes becoming noticeable and tender to the touch. Tenderness is common when the swelling is caused by a temporary process.
The most frequent causes of temporary enlargement are infections occurring in the areas the nodes drain, such as a skin infection on the arm or hand. Upper respiratory infections can also trigger a response in the axilla. Even a recent vaccination in the arm can cause a transient, reactive swelling as the immune system processes the vaccine components.
In most cases, this swelling is self-limiting, resolving on its own within a few weeks once the underlying infection or immune stimulation has passed. A swollen node that is soft, movable, and tender usually indicates a temporary process. Any persistent or unexplained swelling warrants a medical evaluation.
Lymph Nodes and Breast Health Screening
The axillary lymph nodes are the primary drainage route for the majority of breast tissue. Assessing the status of these nodes is a part of breast cancer diagnosis, staging, and prognosis. If breast cancer cells break away from the original tumor, they are likely to travel through the lymphatic vessels and become lodged in the nearby axillary nodes.
Doctors examine the armpit region during physical exams to check for any unusual firmness or enlargement of the nodes. The presence of cancer cells in these nodes indicates that the disease has begun to spread beyond the breast. To determine the extent of this spread, surgeons often perform a procedure called a sentinel lymph node biopsy.
In this procedure, the first one or two nodes to receive drainage from the tumor are identified and removed for testing. If these sentinel nodes are clear of cancer, it suggests that the disease has likely not spread to the rest of the lymph node chain, potentially sparing the patient from more extensive surgery. Conversely, persistent, hard, and non-painful enlargement of an axillary node raises a higher suspicion for malignancy and requires immediate investigation.