The blood vessels supplying the muscle beneath the breast penetrate the fascia and also supply the breast. The main artery to pectoralis muscle and breast is the pectoral branch of the thoracoacromial artery. The medial side of the breast also receives blood from branches of the internal mammary artery. The lateral side of the breast also receives blood from the lateral thoracic artery. The veins draining the breast follow the path of the arteries in the reverse direction.
The breast, like all tissues of the body, contains a rich network of tiny channels called lymphatics. The lymphatics drain fluid from tissues outside of the blood vessels and converge toward major vascular channels. The lymphatics are interrupted by chains of pea-sized lymph nodes which filter the lymph fluid and its contents. The lateral two thirds of the breast drains toward the axillary chain of lymph nodes. Lymphatic channels from the arm also drain through the axillary nodes. Disruption of too many of these pathways when the axillary nodes are sampled for breast cancer, may cause arm swelling (lymphedema). The medial third of the breast drains to the internal mammary chain of nodes lying alongside the breastbone and between the attached rib cartilages. There is also some degree of cross-over drainage as well.
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