Breast

The breast is a modified apocrine gland located on the anterior chest wall, overlying the pectoralis major muscle, typically extending from the second to the sixth rib vertically and from the sternal edge to the midaxillary line horizontally. It is composed of glandular tissue (parenchyma), fibrous connective tissue (stroma), and adipose tissue, all supported by Cooper's ligaments that provide structural integrity.

Anatomical Structure

The glandular component consists of 15–20 lobes, each arranged radially around the nipple. Each lobe is subdivided into lobules, which are the functional milk-producing units. The lobules drain into lactiferous ducts that converge at the nipple. The terminal duct lobular unit (TDLU) is considered the functional and pathological unit of the breast, as most breast carcinomas and benign lesions originate from this structure.

Blood Supply and Lymphatic Drainage

The arterial supply derives primarily from the internal mammary (internal thoracic) artery, lateral thoracic artery, and intercostal perforators. Venous drainage parallels the arterial supply. Lymphatic drainage is clinically significant, with approximately 75% of lymph draining to the ipsilateral axillary lymph nodes, organized into three levels relative to the pectoralis minor muscle. Additional drainage pathways include the internal mammary (parasternal), supraclavicular, and contralateral breast nodes.

Innervation

Sensory innervation is provided by the lateral and anterior cutaneous branches of the 2nd through 6th intercostal nerves. The 4th intercostal nerve is the primary source of nipple-areolar complex sensation.

Development and Function

Breast development (thelarche) begins at puberty under the influence of estrogen and progesterone. The breast undergoes cyclical changes during the menstrual cycle and significant proliferation during pregnancy and lactation under the influence of prolactin and oxytocin. After menopause, glandular tissue involutes and is progressively replaced by adipose tissue.