Axillary Veins

1. Overview

The axillary veins are major veins in the upper extremity that play an essential role in draining deoxygenated blood from the arm, shoulder, and upper chest back into the heart. They are the continuation of the brachial veins and form an important part of the venous return system for the upper body. The axillary veins are located in the axilla (armpit) and drain blood from the upper limb, the chest wall, and parts of the breast. These veins eventually merge with the subclavian veins to form the brachiocephalic veins, which return blood to the superior vena cava and then to the heart. Proper function of the axillary veins is essential for maintaining effective venous return and preventing conditions like edema or venous thrombosis.

2. Location

The axillary veins are located in the axilla, or armpit, a region between the shoulder and the chest. They begin as the continuation of the brachial veins, which drain blood from the arm. The axillary veins travel through the axilla, running posteriorly to the axillary artery. As they move along, they collect venous blood from several tributaries, including veins from the arm, shoulder, chest wall, and breast. The axillary veins eventually merge with the subclavian veins, just beneath the clavicle (collarbone), forming the brachiocephalic veins, which return blood to the superior vena cava and ultimately to the right atrium of the heart.

3. Structure

The axillary veins have a relatively simple structure but are equipped to handle the return of deoxygenated blood from the upper limbs and upper body. Some key structural features of the axillary veins include:

• Size and Length: The axillary veins are medium-sized veins, typically around 1-2 centimeters in diameter in healthy individuals. They extend from the lower border of the teres major muscle (which forms the lower boundary of the axilla) to the junction where they merge with the subclavian veins.

• Tributaries: The axillary veins receive blood from several important tributaries, including:

  • Brachial veins: These veins drain the deep structures of the arm and forearm, including muscles and tissues, and empty into the axillary veins.

  • Basilic vein: The basilic vein, a large superficial vein of the arm, drains blood from the superficial tissues and joins the brachial veins before entering the axillary veins.

  • Cephalic vein: The cephalic vein, another superficial vein in the upper limb, drains blood from the forearm and hand and typically joins the axillary veins at the level of the shoulder.

  • Thoracoepigastric veins: These veins drain blood from the chest wall and abdomen, and their tributaries also drain into the axillary veins.

• Valves: Like other veins, the axillary veins contain one-way valves that prevent the backflow of blood and facilitate the upward return of blood toward the heart, particularly against the force of gravity. These valves are critical in preventing venous stasis and aiding in the efficient return of blood to the superior vena cava.

• Adjacent structures: The axillary veins lie just posterior to the axillary artery and are in close proximity to important nerves, such as the brachial plexus, which can be important when performing medical procedures in the region (e.g., central line placement).

4. Function

The primary function of the axillary veins is to return deoxygenated blood from the upper body back to the heart. This is essential for maintaining circulatory efficiency and for ensuring that waste products from the metabolism of the upper limb muscles and tissues are removed properly. The key functions of the axillary veins include:

• Venous return: The axillary veins are part of the venous return system, ensuring that deoxygenated blood from the upper limb, shoulder, chest wall, and part of the breast is carried back to the heart. This blood returns through the subclavian veins and ultimately to the right atrium via the brachiocephalic veins and superior vena cava.

• Prevention of venous stasis: The axillary veins, with their one-way valves, help prevent the backflow of blood, especially when blood is returning from the lower parts of the upper extremity against gravity. This prevents blood from pooling in the limbs and facilitates proper circulation.

• Support of lymphatic return: The axillary veins also work in conjunction with the lymphatic system to return lymphatic fluid (which is a clear fluid that carries white blood cells) from the tissues of the arm and chest back to the central circulation, thus maintaining fluid balance in the body.

5. Physiological Role(s)

The axillary veins have several key physiological roles that contribute to the health of the cardiovascular system and the proper functioning of the upper limbs and upper body:

• Efficient blood circulation: By providing a direct pathway for deoxygenated blood from the upper limbs and chest to the heart, the axillary veins ensure that the circulatory system operates efficiently. This is critical during physical activity, when the body requires more oxygen and nutrients for muscle function.

• Regulation of blood pressure: The proper functioning of the axillary veins helps maintain normal blood pressure in the upper limbs. By facilitating venous return, the axillary veins play a role in regulating the volume of blood returning to the heart, which in turn influences overall blood pressure.

• Pressure management: The axillary veins contribute to managing the venous pressure within the arm and shoulder. This function is particularly important during physical exertion, such as lifting or carrying heavy objects, as it helps ensure that blood flows back to the heart without causing damage to the veins or heart.

• Adaptation during physical activity: The axillary veins help adapt to increased circulation demands during exercise or other physical activities. By efficiently draining blood from the upper body, the axillary veins facilitate optimal oxygen delivery to muscles and tissues during exertion.

6. Clinical Significance

The axillary veins are clinically significant because dysfunction or obstruction of these veins can lead to several serious conditions, including venous thrombosis, lymphedema, and compromised circulation. Some important clinical conditions related to the axillary veins include:

• Axillary vein thrombosis (AVT): AVT is a condition in which a blood clot forms in the axillary veins, often as a result of prolonged immobility, trauma, or certain medical conditions such as cancer. AVT can cause symptoms such as swelling, pain, and discoloration of the arm, and if left untreated, it can lead to complications such as post-thrombotic syndrome (chronic pain and swelling) or pulmonary embolism (if the clot dislodges and travels to the lungs).

• Subclavian-axillary vein thrombosis: This condition, also known as Paget-Schroetter syndrome, occurs when there is a blockage in the subclavian and axillary veins, often due to repetitive motion or compression of the veins in the thoracic outlet (the space between the collarbone and the first rib). This can result in swelling, arm pain, and difficulty moving the arm.

• Central venous catheter placement: The axillary veins are often used as access points for central venous catheter (CVC) placement. This is done to administer medications, fluids, or for hemodialysis. Incorrect placement or complications during insertion can lead to infection, thrombosis, or injury to surrounding structures such as nerves and arteries.

• Lymphedema: The axillary veins also work in conjunction with the lymphatic system, and blockage or damage to these veins (or the surrounding lymphatic vessels) can lead to lymphedema, which is swelling caused by a buildup of lymphatic fluid in the tissues. Lymphedema is common after axillary lymph node dissection, particularly in breast cancer treatment.

• Venous insufficiency: Chronic venous insufficiency in the axillary veins can lead to symptoms such as swelling, fatigue, and skin changes in the upper limbs. This condition can be caused by valve dysfunction or venous reflux, where blood flows backward due to faulty valve function, leading to pooling of blood in the veins.

The axillary veins are critical for the efficient drainage of deoxygenated blood from the upper extremities and chest. Dysfunction in the axillary veins can lead to conditions such as venous thrombosis, lymphedema, and compromised circulation, which can negatively impact the function of the upper limb and overall cardiovascular health. Early detection and appropriate management of these conditions are essential to prevent complications and ensure optimal circulatory function.