The junction of the shoulder and the upper arm form a joint that is movable, allowing a person to reach, extend and rotate the arm. The cavity under this joint, commonly referred to as the armpit, is known as the axilla. More than simply sweat glands and armpit hair, the axilla contains components such as circulatory vessels, nerves and lymph nodes. All of these elements are contained within a pyramid-shaped hollow area between the arm, shoulder and side wall of the chest.
The axillary cavity is bordered by muscles on both sides. The front side, toward the chest, contains the pectoralis muscles, while the posterior portion consists of the latissimus dorsi muscles of the back. The area is also composed of bony portions that give it structure, including those of the upper arm and the bone of the shoulder, called the scapula. The bottom and top portions of the axilla are also formed from ribs of the side chest wall and the collarbone, respectively.
The armpit contains lymph nodes that are part of the system that drains lymph from the upper arm, shoulder and neck. The lymphatic system serves to protect the body’s immunity by moving particles such as bacteria and toxins within lymph throughout these specialized channels. Axillary lymph nodes can become swollen, which may be a sign of infection. When lymph nodes carry particles such as bacteria or cancer cells, it can be a sign of infection or disease and is frequently felt as a lump in the armpit.
The axilla is covered by skin and has hair growth after puberty. Frequently referred to as “underarm hair,” some women choose to shave this region, although cultural attitudes toward axillary hair vary. The axilla also contains apocrine sweat glands, which are found under the skin. After puberty, the apocrine glands excrete sweat under the arm, which produces an odor when it comes in contact with bacteria on the skin. For this reason, many people choose to use underarm deodorant or antiperspirant to mask or prevent some of the scent.
The axilla contains branches of a major nerve called the brachial plexus, the nerve that supplies sensation to most of the muscles in the upper portion of the arm. As a result, injury to the axilla can damage the brachial plexus and affect nerve sensation throughout the upper arm. The armpit also contains the axillary artery and the axillary vein, which run side by side and are connected to larger vessels. A sharp injury to the axilla can result in a large amount of blood loss and the potential for air to enter the subclavian vein, which is connected to the axillary vein.