Axilla (Armpit) PART-3

NEET PG Anatomy
#1

Axilla (Armpit) PART-3

CONTENTS OF THE AXILLA

Ø The contents of axilla are

  1. Axillary artery and its branches.

  2. Axillary vein and its tributaries.

  3. Cords of brachial plexus.

  4. Axillary lymph nodes.

  5. Fibrofatty tissue

  6. Axillary tail of breast.

  7. Long thoracic and intercostobrachial nerve.

AXILLARY ARTERY

Ø The axillary artery is the main artery of the upper limb. It begins at the outer border of the first rib as the continuation of subclavian artery and ends by becoming brachial artery at the lower border of teres major. In axilla, it runs from its apex to the base along the lateral wall nearer to the anterior wall than the posterior wall. During its course through axilla, it is crossed on its superficial aspect by the pectoralis minor muscle, which divides it into three parts. The axillary vein is medial to the artery and the cords of brachial plexus are arranged around the second part of the artery, the lateral cord being lateral, the medial cord medial, and posterior cord behind.

PART

Ø The axillary artery is divided into the following three parts by the pectoralis minor:

  1. First part, superior (or proximal) to the muscle.

  2. Second part, posterior (or deep) to the muscle.

  3. Third part, inferior (or distal) to the muscle.

RELATIONS

Ø The axillary vein lies medial to the axillary artery throughout its course, but the relationship of cords of brachial plexus and their branches are different for each of the three parts of the artery.The relations of the three parts of the axillary artery are given in the table.

BRANCHES OF THE AXILLARY ARTERY

Ø The axillary artery gives six branches: one branch from first part, two branches from the second part, and three branches from third part. Most of these branches go to and supply walls of the axilla.

A. From first part - Superior thoracic artery, a very small branch, arise near the Subclavius, passes between the pectoralis major and minor muscles, and supplies these muscles and medial wall of the axilla.

B. From second part -1. Thoraco-acromial artery (acromiothoracic artery), emerges at the upper border of pectoralis minor, pierces clavipectoral fascia and soon breaks up into four branches: (a) pectoral branch, (b) deltoid branch, © acromial branch, and (d) clavicular branch. These branches radiate at right angle to each other. The pectoral branch supplies pectoral muscles, deltoid branch, ends by joining anastomosis over the acromion, clavicular branch supplied sternoclavicular joint.

  1. Lateral thoracic artery, emerges at and runs along the inferior border of pectoralis minor, supplying the branches to pectoralis major and minor and serratus anterior muscles. In the females, the lateral thoracic artery is large and provides important supply to the breast through its lateral mammary branches.

C. From third ptart - 1.Subscapular artery, the largest branch of axillary artery, runs along the lower border of the subscapularis and ends near the inferior angle of the scapula. It gives a large branch, the circumflex scapular artery, which passes through upper triangular intermuscular space, winds round the lateral border of scapula to enter infraspinous fossa. In addition, it gives numerous small branches.

  1. Anterior circumflex humeral artery, a small branch, passes in front of surgical neck of humerus and anastomoses with the posterior circumflex humeral artery to form an arterial circle around the surgical neck of humerus. It gives an ascending branch, which runs upwards into the intertubercular sulcus of humerus to supply the head of humerus and shoulder joint.

  2. Posterior circumflex humeral artery, larger than the anterior circumflex humeral artery, passes backwards, along with axillary nerve through the quadrangular intermuscular space, crosses the posterior aspect of surgical neck of humerus to anastomose with the anterior circumflex humeral artery. It supplies the deltoid muscle and shoulder joint.

Arterial Anastomosis Around Scapula(Scapular Anastomosis)

Ø The arterial anastomosis around scapula is principally formed between the branches of the first part of the subclavian and the third part of the axillary arteries.

Ø The scapular anastomosis takes place at two sites: around the body of scapula and over the acromion process of the scapula.

  1. Around the body of scapula: It occurs between the

a) suprascapular artery, a branch of the thyrocervical trunk from the first part of the subclavian artery,

b) circumflex scapular artery, a branch of the subscapular artery from the third part of the axillary artery, and

c) deep branch of the transverse cervical artery, a branch of the thyrocervical trunk.

  1. Over the acromion process: It occurs between the

a) acromial branch of the thoraco-acromial artery,

b) acromial branch of the suprascapular artery, and

c) acromial branch of the posterior circumflex humeral artery.

Clinical correlation

Ø Collateral circulation through scapular anastomosis: If the subclavian and axillary arteries are blocked anywhere between 1st part of subclavian artery and 3rd part of axillary artery, the scapular anastomosis serves as a potential pathway (collateral circulation) between the first part of the subclavian artery and the third part of the axillary artery, toensure the adequate circulation to the upper limb.