Axillary artery

The axillary artery is a major blood vessel that supplies blood to the upper limb, chest wall, and shoulder region. It is a continuation of the subclavian artery and becomes the brachial artery as it travels down the arm. The axillary artery is divided into three parts based on its location relative to the pectoralis minor muscle, and each part gives off several important branches that supply the surrounding muscles and tissues.

Location

The axillary artery begins at the outer border of the first rib, as a continuation of the subclavian artery. It travels through the axilla (armpit region), running deep to the pectoralis minor muscle. The artery is divided into three parts:

• The first part is proximal to the pectoralis minor.
• The second part lies posterior to the pectoralis minor.
• The third part is distal to the pectoralis minor and continues down the arm.

Structure and Anatomy

The axillary artery is a major vessel in the upper limb that supplies blood to the shoulder, chest wall, and arm. It is a continuation of the subclavian artery and becomes the brachial artery as it descends into the arm. Below is a detailed description of its anatomy, including its divisions, branches, and relationships with surrounding structures.

Origin

The axillary artery originates as the continuation of the subclavian artery at the lateral border of the first rib. It then travels through the axillary region (armpit) and terminates at the lower border of the teres major muscle, where it becomes the brachial artery.

Course

The axillary artery runs through the axilla, following a slightly curved course from the lateral border of the first rib to the lower border of the teres major muscle. It is divided into three parts based on its relationship to the pectoralis minor muscle.

First Part

The first part of the axillary artery lies proximal (medial) to the pectoralis minor muscle.

• Extent: This segment extends from the lateral border of the first rib to the upper border of the pectoralis minor muscle.
• Location: It is relatively superficial and covered by the pectoralis major muscle.

Second Part

The second part lies posterior to the pectoralis minor muscle.

• Extent: This portion extends from the upper border to the lower border of the pectoralis minor muscle.
• Location: It is deeper and more protected, being covered by the pectoralis minor muscle itself.

Third Part

The third part lies distal (lateral) to the pectoralis minor muscle.

• Extent: It extends from the lower border of the pectoralis minor to the lower border of the teres major muscle, where it continues as the brachial artery.
• Location: This part is relatively superficial again as it exits from beneath the pectoralis minor.

Branches

The axillary artery gives off multiple branches, supplying blood to the surrounding muscles, bones, and skin of the shoulder and upper limb. These branches arise from the different parts of the axillary artery, and each part has specific branches.

Branches of the First Part

There is one major branch arising from the first part of the axillary artery:

Superior Thoracic Artery: This artery supplies the upper part of the thoracic wall, including the upper part of the serratus anterior muscle and intercostal spaces.

Branches of the Second Part

The second part of the axillary artery gives off two major branches:

• Thoraco-acromial Artery: This artery branches into four divisions: the pectoral, acromial, clavicular, and deltoid branches. These branches supply the pectoralis major, pectoralis minor, deltoid, clavicle, and surrounding areas.
• Lateral Thoracic Artery: This artery runs along the lateral thoracic wall, supplying the serratus anterior, pectoralis muscles, and in females, the lateral aspect of the breast.

Branches of the Third Part

The third part of the axillary artery gives off three major branches:

• Subscapular Artery: This is the largest branch of the axillary artery. It quickly divides into the circumflex scapular artery and the thoracodorsal artery, which supply the muscles and structures around the scapula and the latissimus dorsi.
• Anterior Circumflex Humeral Artery: This smaller artery runs around the front of the humeral neck, forming an anastomosis with the posterior circumflex humeral artery, supplying blood to the shoulder joint and surrounding muscles.
• Posterior Circumflex Humeral Artery: This artery is larger than the anterior circumflex humeral artery. It travels posteriorly through the quadrangular space (bounded by the teres minor, teres major, long head of the triceps, and surgical neck of the humerus) and forms an anastomosis with the anterior circumflex humeral artery. It supplies the deltoid, teres minor, and triceps muscles, as well as the shoulder joint.

Relationship to Surrounding Structures

The axillary artery is closely related to several important structures in the axilla, including muscles, veins, nerves, and lymph nodes.

Pectoralis Major and Minor Muscles

The axillary artery is located deep to the pectoralis major muscle throughout its course. The second part of the artery is found posterior to the pectoralis minor, which divides the artery into its three parts. The close relationship with these muscles makes the artery relatively protected in this region.

Axillary Vein

The axillary vein lies medial to the axillary artery throughout most of its course. It begins at the lower border of the teres major and runs alongside the artery, draining blood from the upper limb into the subclavian vein. The close proximity of the artery and vein is important in surgeries and medical procedures in the axilla.

Brachial Plexus

The brachial plexus, a network of nerves that supplies the upper limb, is closely associated with the axillary artery. The cords of the brachial plexus (lateral, posterior, and medial) surround the second part of the axillary artery. This relationship is important when considering injuries or surgical approaches in the axillary region, as damage to either the artery or the brachial plexus could affect the function of the upper limb.

Axillary Lymph Nodes

The axillary artery is surrounded by numerous axillary lymph nodes, which are involved in draining lymph from the upper limb, chest wall, and breast. These lymph nodes are clinically significant, especially in cases of breast cancer, where they are examined for metastatic spread.

Quadrangular Space

The posterior circumflex humeral artery passes through the quadrangular space, which is bordered by the teres minor, teres major, long head of the triceps, and surgical neck of the humerus. This anatomical area is important because compression or injury to this space can affect the artery, leading to compromised blood supply to the shoulder region.

Termination

The axillary artery terminates at the lower border of the teres major muscle, where it continues as the brachial artery. The brachial artery is the main vessel that supplies blood to the arm, extending all the way down to the hand. At the point of termination, the axillary artery has already supplied most of the shoulder and upper thoracic wall, and its transition to the brachial artery marks the beginning of blood supply to the arm.

Variations

The anatomy of the axillary artery can show some variations, particularly in its branches. Common variations include:

• Origin of Branches: Some branches of the axillary artery may arise from different parts than usual. For example, the lateral thoracic artery may arise directly from the thoraco-acromial artery or subscapular artery instead of from the second part of the axillary artery.
• Number of Branches: In some cases, there may be additional small branches or variations in the size and distribution of the main branches.

Function

The axillary artery is the primary vessel that supplies blood to the upper limb, shoulder, and parts of the chest wall. As it travels through the axilla, it provides oxygenated blood to numerous muscles, bones, and other tissues. Its role is crucial for maintaining proper function and movement in the upper limb. Below is a detailed description of its specific functions based on its branches and their areas of supply.

Blood Supply to the Upper Thoracic Wall

The superior thoracic artery, which branches from the first part of the axillary artery, is responsible for supplying blood to the upper thoracic wall.

• Nourishment of Upper Thoracic Muscles: The superior thoracic artery supplies blood to the serratus anterior muscle and the intercostal muscles in the upper chest region. These muscles are involved in breathing and shoulder movements.
• Support for Intercostal Spaces: The artery also provides blood to the first and second intercostal spaces, ensuring that the muscles and skin in these areas receive adequate oxygen and nutrients.

Blood Supply to the Pectoral Region and Shoulder

The thoraco-acromial artery (a branch of the second part of the axillary artery) provides blood to the pectoralis muscles, deltoid muscle, clavicle, and acromion. This artery divides into four smaller branches, each serving a specific region:

• Pectoral Branch: This branch supplies blood to the pectoralis major and pectoralis minor muscles. These muscles are involved in movements of the shoulder, such as adduction and internal rotation.
• Deltoid Branch: The deltoid branch supplies blood to the deltoid muscle, which plays a key role in shoulder abduction, flexion, and extension.
• Acromial Branch: The acromial branch supplies the acromion and surrounding soft tissues, contributing to the blood supply of the shoulder joint.
• Clavicular Branch: This branch supplies the clavicle and the sternoclavicular joint, helping maintain the structural integrity and movement of the clavicle.

Blood Supply to the Lateral Thoracic Wall

The lateral thoracic artery, another branch of the second part of the axillary artery, plays a vital role in supplying blood to the lateral thoracic wall and breast tissue (in females).

• Nourishment of the Serratus Anterior: The lateral thoracic artery delivers blood to the serratus anterior muscle, which is crucial for protracting the scapula and stabilizing the shoulder blade during arm movements.
• Blood Supply to the Breast: In females, the lateral thoracic artery supplies blood to the lateral portion of the breast, contributing to the overall vascularization of the breast tissue, especially during periods of growth or lactation.

 Blood Supply to the Scapular Region

The subscapular artery, which is the largest branch of the axillary artery, provides blood to the scapular and posterior thoracic regions through its two main branches:

• Circumflex Scapular Artery: This branch supplies the teres major, teres minor, and infraspinatus muscles. These muscles are involved in rotating and stabilizing the shoulder joint. It also supplies blood to the scapula itself, ensuring proper bone health and repair.
• Thoracodorsal Artery: This artery supplies the latissimus dorsi muscle, which is responsible for shoulder extension, adduction, and internal rotation. The thoracodorsal artery ensures that the latissimus dorsi receives adequate oxygen and nutrients to function properly during movements like pulling and lifting.

Blood Supply to the Shoulder Joint and Humeral Head

The anterior and posterior circumflex humeral arteries, which arise from the third part of the axillary artery, play a key role in supplying blood to the shoulder joint and humeral head.

• Anterior Circumflex Humeral Artery: This artery wraps around the front of the surgical neck of the humerus, supplying blood to the anterior part of the shoulder joint, the glenohumeral joint capsule, and the humeral head. It ensures the proper health and function of the shoulder’s bony structures.
• Posterior Circumflex Humeral Artery: This artery is larger and passes through the quadrangular space, supplying blood to the deltoid muscle, teres minor, and long head of the triceps brachii. It also contributes to the blood supply of the shoulder joint and forms an anastomosis with the anterior circumflex humeral artery, ensuring a continuous supply of blood to the humeral head and joint capsule.

Blood Supply to the Upper Limb

The axillary artery’s continuation into the brachial artery marks its transition to supplying blood to the arm and forearm.

Transition to Brachial Artery: At the lower border of the teres major muscle, the axillary artery becomes the brachial artery, which is the primary blood vessel supplying the muscles and tissues of the upper arm, elbow, and forearm. This ensures that the entire upper limb receives sufficient oxygen and nutrients to maintain its function during activities such as lifting, pushing, and manipulating objects.

Oxygen and Nutrient Delivery

Like all arteries, the primary function of the axillary artery is to deliver oxygenated blood and nutrients to the tissues it supplies. This is critical for the health, maintenance, and repair of muscles, bones, joints, and skin in the shoulder and upper limb regions.

• Muscle Function and Endurance: The muscles in the shoulder, chest, and upper limb rely on the continuous supply of oxygen and nutrients delivered by the axillary artery to function properly during activities such as lifting, pulling, pushing, and overhead movements.
• Tissue Repair and Healing: The blood supply provided by the axillary artery is essential for tissue repair and healing after injuries, such as muscle strains, shoulder dislocations, or fractures of the humerus or scapula. Adequate blood flow supports the healing process by delivering oxygen, nutrients, and immune cells to the damaged tissues.

Support for Collateral Circulation

The axillary artery and its branches form part of an extensive network of collateral circulation, which ensures that blood flow to the upper limb remains adequate even if one of the major arteries is blocked or damaged.

Anastomoses with Other Arteries: The circumflex humeral arteries and the subscapular artery form anastomoses with other vessels in the shoulder region, such as the suprascapular artery and the dorsal scapular artery, to maintain continuous blood flow. This collateral circulation helps prevent ischemia (lack of blood supply) in the shoulder and upper limb during activities or in cases of injury.

Clinical Significance

The axillary artery is of great clinical importance due to its role in supplying blood to the upper limb, shoulder, and chest wall. Key points of its clinical significance include:

• Surgical Procedures: The axillary artery is a vital structure during surgical procedures such as shoulder surgeries, axillary lymph node dissections, and trauma management. Surgeons must be cautious to avoid damaging this artery, as it could lead to significant blood loss and impaired blood flow to the upper limb.
• Trauma and Injury: Injuries to the axilla, such as fractures of the humerus or shoulder dislocations, can damage the axillary artery. Compromise of this vessel can lead to serious complications such as ischemia or loss of function in the upper limb due to insufficient blood supply.
• Collateral Circulation: The axillary artery forms an important part of the collateral circulation network in the shoulder and upper limb. Its branches, such as the circumflex humeral and subscapular arteries, help maintain continuous blood flow, even when primary vessels are blocked or injured.
• Aneurysm: The axillary artery can be involved in rare cases of aneurysm, which could result in compression of nearby nerves and veins, leading to neurological deficits or vascular complications in the upper limb.