Axillary artery

INTRODUCTION:

• In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla (armpit) and the upper limb. 
• Its origin is at the lateral margin of the first rib, before which it is called the subclavian artery.
• Cords of brachial plexus are named as per relation with axillary artery behind teres major.

STRUCTURE:

The axillary artery is often referred to as having three parts, with these divisions based on its location relative to the Pectoralis minor muscle, which is superficial to the artery.

• First part – the part of the artery above the pectoralis minor
• Second part – the part of the artery that lies behind the pectoralis minor
• Third part – the part of the artery below the pectoralis minor.

RELATIONS:

• The axillary artery is accompanied by the axillary vein, which lies medial to the artery, along its length.
• In the axilla, the axillary artery is surrounded by the brachial plexus.
•  The second part of the axillary artery is the reference for the locational descriptions of the cords in the brachial plexus. 
• For example, the posterior cord of the brachial plexus is so named because it lies posterior to the second part of the artery.

BRANCHES:

• Axillary artery is divided into 3 parts by pectoralis minor muscle. 
• Axillary artery extends from the outer border of the first rib to inferior border of teres major muscle where it becomes the brachial artery. 

First part (1 branch)

• Superior thoracic artery (Supreme thoracic artery)

Second part (2 branches)

• Thoraco-acromial artery
• Lateral thoracic artery.( If the lateral thoracic artery is not branching from the axillary artery, will most likely branch from the following (in order of likelihood): (1) thoracoacromial, (2) third part of axillary artery, (3) suprascapular artery, (4) subscapular artery)

Third part (3 branches)

• Subscapular artery()
• Anterior humeral circumflex artery
• Posterior humeral circumflex artery
• Continues as the brachial artery past the inferior border of the teres major.

CLINICAL SIGNIFICANCE:

• The axillary artery may be safely clamped without endangering the arm, but only in a location proximal to the origin of the subscapular artery (and distal to the thyrocervical trunk of the subclavian artery).
•  The anastomotic network surrounding the scapula provides an alternate path for collateral circulation to the arm from arteries including the dorsal scapular artery and suprascapular artery.
• The right axillary artery is often used as an arterial cannulation site in cardiac surgery, particularly for repair of aortic dissection and replacement of the ascending aorta and aortic arch.
• The suprascapular and dorsal scapular arteries arise, directly or indirectly, from the subclavian artery while the subscapular and scapular circumflex arteries are from the third part of the axillary artery, thus providing a bypass for obstructions of the first or second parts of the axillary artery.

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