Axillary Arteries

1. Overview

The axillary arteries are major blood vessels that provide oxygenated blood to the upper limb, including the shoulder, arm, and part of the chest. They are a continuation of the subclavian arteries and pass through the axilla (armpit) before branching into smaller arteries that supply the arm, chest, and shoulder regions. The axillary arteries play a critical role in delivering blood to the upper extremities, which are essential for movement, dexterity, and overall function of the arms. The axillary arteries are important both for their role in circulation and in providing a route for the distribution of blood to tissues critical for muscle activity and metabolic processes in the upper body.

2. Location

The axillary arteries are located in the axilla, which is the area under the shoulder joint where the arm connects to the torso. The axillary artery is a continuation of the subclavian artery, which passes over the first rib into the axilla. The artery runs from the outer border of the first rib to the inferior border of the teres major muscle (a muscle in the upper arm). After this, it transitions into the brachial artery, which supplies blood to the arm. The axillary artery lies deep within the axillary region and is in close proximity to several important structures, including the brachial plexus (the network of nerves controlling the arm and hand) and various veins.

3. Structure

The axillary artery is a large, muscular artery with several distinctive structural features that help it supply blood to the upper limbs and surrounding areas. These features include:

• Origin: The axillary artery begins as a continuation of the subclavian artery at the outer border of the first rib. It passes through the axilla, where it supplies blood to the shoulder, arm, and chest.

• Segments: The axillary artery is commonly divided into three parts based on its anatomical relationship to the pectoralis minor muscle:

  • First part: The first part of the axillary artery lies between the outer border of the first rib and the medial border of the pectoralis minor muscle.

  • Second part: The second part is located behind the pectoralis minor muscle.

  • Third part: The third part extends from the lateral border of the pectoralis minor muscle to the inferior border of the teres major muscle, where it transitions into the brachial artery.

• Branches: The axillary artery gives rise to several important branches, including:

  • Superior thoracic artery: This branch supplies blood to the upper chest and the first two intercostal spaces (spaces between the ribs).

  • Thoracoacromial artery: This artery supplies blood to the chest wall, shoulder, and the upper part of the arm.

  • Lateral thoracic artery: It supplies the lateral part of the chest wall and the breast tissue, as well as the serratus anterior muscle.

  • Subscapular artery: This is one of the largest branches of the axillary artery and supplies the subscapularis muscle (a muscle of the shoulder), along with the muscles of the back.

  • Anterior and posterior circumflex humeral arteries: These branches supply blood to the shoulder joint and the deltoid muscle, which plays a key role in arm movement.

4. Function

The primary function of the axillary artery is to deliver oxygenated blood to the shoulder, arm, and upper chest. Its functions include:

• Blood supply to the upper limb: The axillary artery is responsible for delivering oxygen-rich blood to the muscles, bones, skin, and tissues of the shoulder, arm, and chest. This ensures that the upper extremities receive the oxygen and nutrients needed to carry out their functions, including movement, sensation, and metabolic activities.

• Facilitating arm movement: Through its branches, the axillary artery supplies blood to muscles such as the deltoid, pectoralis major, and biceps brachii, which are involved in arm and shoulder movement. These muscles are essential for performing tasks such as lifting, pushing, and carrying.

• Blood supply to the chest: The axillary artery supplies blood to the chest wall and parts of the breast tissue, ensuring that these regions receive the necessary oxygen for cellular function and tissue health.

• Providing nutrients to shoulder structures: The axillary artery’s branches, including the subscapular artery, help supply blood to the shoulder muscles and joints. This contributes to the maintenance of joint mobility and muscle function in the upper body.

5. Physiological Role(s)

The axillary artery has several physiological roles that contribute to the health and function of the upper body, particularly the arm and shoulder:

• Support of upper limb function: The axillary artery ensures that the upper limb receives a continuous and adequate supply of oxygenated blood, allowing for normal muscle function, strength, and endurance during daily activities such as lifting, writing, or typing.

• Efficient circulation to the shoulder and chest: The branches of the axillary artery provide essential blood supply to the shoulder muscles and the chest wall. This helps maintain structural integrity, muscle tone, and flexibility in these areas, which is important for overall body posture and physical activity.

• Regulation of circulation during physical activity: During exercise or physical activity, the axillary artery helps meet the increased blood demand of the upper extremities. This allows the muscles to function optimally by ensuring they receive more oxygen and nutrients to fuel movement.

• Thermoregulation: By supplying blood to the skin and muscles of the upper limbs and chest, the axillary artery plays a role in thermoregulation, helping the body regulate temperature by allowing for heat dissipation through the skin during physical exertion.

6. Clinical Significance

The axillary artery is clinically significant because it supplies vital blood to the upper extremities. Several conditions can affect the axillary artery, leading to reduced blood flow and ischemia (lack of oxygen) in the affected tissues. Some clinical conditions associated with the axillary artery include:

• Axillary artery aneurysm: An aneurysm is a localized dilation of the artery, which can occur in the axillary artery due to conditions such as atherosclerosis or trauma. Aneurysms can lead to arterial rupture, which can cause severe bleeding and other complications. Treatment typically involves surgical repair or endovascular intervention to prevent rupture.

• Thoracic outlet syndrome (TOS): TOS is a condition caused by compression of the neurovascular structures in the thoracic outlet, which includes the axillary artery and the brachial plexus (the network of nerves controlling the arm and hand). Symptoms of TOS include pain, numbness, and weakness in the arm, which can result from decreased blood flow or nerve compression in the axillary region. Treatment may involve physical therapy, medication, or surgery to relieve the compression.

• Peripheral artery disease (PAD): PAD occurs when there is a narrowing or blockage in the arteries that supply blood to the legs, but it can also affect the axillary artery. PAD in the axillary artery can cause symptoms such as arm pain, cramping, and difficulty moving the arm. Treatment may involve lifestyle changes, medication, or surgical intervention to restore blood flow.

• Axillary artery injury: Trauma to the axillary artery, such as from blunt force or penetrating injury, can lead to hemorrhage and compromised blood flow to the arm. If left untreated, this can result in ischemia, tissue death, or limb loss. Immediate medical attention is necessary for managing axillary artery injuries, and surgical repair may be required to restore blood flow.

• Subclavian steal syndrome: This syndrome occurs when there is a stenosis (narrowing) in the subclavian artery, which can affect the blood flow to the axillary artery. As a result, blood flow is redirected from the vertebral artery to the arm, causing symptoms like dizziness, visual disturbances, and weakness. Treatment may include surgical intervention or stenting to restore normal blood flow.

The axillary artery is critical for supplying blood to the upper limb and chest, ensuring that the tissues receive the necessary oxygen and nutrients for proper function. Dysfunction of the axillary artery can lead to ischemia, muscle weakness, and other complications. Early diagnosis and intervention are crucial for managing conditions affecting the axillary artery and preserving upper limb function and circulation.