Upper Limb Anatomy - Axilla

Upper Limb Anatomy - Axilla

• The axilla (armpit) is a pyramid-shaped space between the upper arm and the side of the chest.
• Its function is to act as an important passageway for nerves, blood, and lymph vessels traveling from the neck to the upper limb.
• The axilla narrows when the arm is adducted (pulled towards the body) and widens when the arm is abducted (pulled away from the body).
• The axilla has an apex, base, and four walls (anterior, posterior, medial, and lateral).

Axillary Inlet (Apex)

• Bounded by the clavicle, upper border of the scapula, and the outer border of the first rib.
• Serves as a communication channel between the axilla and the neck.
• Vessels and nerves pass through this opening to reach the axilla from the body.

Axilla Boundaries

• Apex: Formed by the clavicle, upper border of the scapula, and the first rib.
• Base: Formed by the skin stretching between the anterior and posterior walls. Anterior axillary fold created by the lower border of the pectoralis major muscle. Posterior axillary fold created by the tendons of latissimus dorsi and teres major muscle. Medially by ribs 4-5 and the chest wall.
• Anterior Wall: Composed of the pectoralis major, pectoralis minor, subclavius muscles, and clavipectoral fascia.
• Posterior Wall: Consists of the subscapularis, latissimus dorsi, and teres major muscles.
• Medial Wall: Formed by the serratus anterior muscle, upper 4-5 ribs, and intercostal muscles.
• Lateral Wall: Consists of the coracobrachialis, biceps brachii, and the bicipital groove of the humerus.

Axillary Contents

• Axillary Artery: Starts at the lateral border of the first rib as a continuation of the subclavian artery; terminates at the lower border of the teres major muscle, becoming the brachial artery.
• Axillary Vein: Continues the brachial vein at the lower margin of the teres major; becomes the subclavian vein at the outer border of the first rib.
• Brachial Plexus: A complex network of nerves in the axilla.
• Axillary Lymph Nodes: Approximately 20-30 nodes, arranged in five groups (humeral, pectoral, subscapular, central, and apical), draining an extensive area of the upper limb, upper back, shoulder, lower neck, chest, and upper abdominal wall.

Axillary Artery Segments

• The pectoralis minor muscle divides the axillary artery into three parts:
• First Part: Above the pectoralis minor muscle.
• Second Part: Behind the pectoralis minor muscle.
• Third Part: Below the pectoralis minor muscle.

Axillary Artery Branches

• First Part (Superior Thoracic Artery): A small artery running between the pectoral muscles, supplying the side of the chest in the upper two intercostal spaces.
• Second Part (Lateral Thoracic Artery): Runs along the lower border of the pectoralis minor, supplying the pectoral muscles, serratus anterior, and breast.
• Second Part (Thoracoacromial Artery): Passes along the upper border of the pectoralis minor, piercing the clavipectoral fascia, and dividing into four branches (pectoral, acromial, clavicular, and deltoid).
• Third Part (Subscapular Artery): A large branch passing towards the inferior angle of the scapula, accompanied by the thoracodorsal nerve, and providing branches for circumflex scapular, thoracodorsal, posterior humeral circumflex, and anterior humeral circumflex arteries.
• Third Part (Anterior and Posterior Circumflex Humeral Arteries): Surround the surgical neck of the humerus (anteriorly and posteriorly), anastomose with each other, and supply the shoulder joint.

Axillary Vein

• Continuation of the brachial vein.
• Becomes the subclavian vein at the outer border of the first rib.
• Similar tributaries to the branches of the axillary artery.
• Lies on the medial side of the artery.

Axillary Sheath

• Axillary sheath enclosing the axillary artery and brachial plexus.
• It contains the axillary vein, but is not strictly a content due to its expansion ability allowing increased venous return.

Efferent Lymphatic Vessels

• Efferent (outgoing) vessels from the apical lymph node group form the subclavian trunk.
• On the left, the subclavian trunk joins the thoracic duct.
• On the right, it joins the venous system at the junction of the right subclavian and internal jugular veins.

Axillary Lymph Node Groups

• Divided into five groups based on location: humeral (lateral), pectoral (anterior), subscapular (posterior), central, and apical.

Explore the intricate anatomy of the axilla, a critical passageway in the upper limb. This quiz covers the boundaries, apex, and functions of the axilla, including its role in nerve and blood vessel transport. Test your knowledge on this essential part of upper limb anatomy.