Human Anatomy, Part 2 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2008

Special Section
Sense organs, organa sensuum
Mammary glands

In addition to sweat and Sebaceous Glands located in the dermis, the Mammary Glands (Fig. 238) are also considered part of the Integumentary System, as they represent evolutionarily modified Sweat Glands.

The mammary glands, glandulae mammariae (Greek: mastos), are underdeveloped in males, while in females they are situated on the Fascia of the pectoralis major Muscle between the III and VI (occasionally VII) Ribs, extending between the parasternal and anterior axillary lines. The shape and size of the female breast vary depending on age, the degree of Development of the reproductive Organs, The amount of adipose tissue surrounding the glandular parenchyma, and the stages of Pregnancy and Lactation.

The Skin overlying the breast is thin, and the subcutaneous adipose tissue surrounding the gland forms its adipose capsule, capsula adiposa. The body of the mammary gland is shaped like a convex disc, 10–12 cm in diameter and 2.5–3 cm thick. Due to the irregular contours of the gland's base, its subclavian, axillary, and one or two abdominal processes are distinguished—areas that are frequently prone to tumors with characteristic clinical courses.

Class="center">

Fig. 238. Mammary gland, glandula mammariae (sagittal section)

The mammary gland is enclosed in a Connective Tissue capsule, capsula fibrosa. In a sexually mature woman, the gland consists of 15–20 lobes, lobus glandulae mammariae, which are complex branched alveolar glands. Their excretory ducts are known as lactiferous ducts, ductus lactiferi. These converge radially toward the apex of the nipple, papilla mammae—a crucial anatomical feature to consider during surgical incisions. Before opening onto the nipple, the lactiferous ducts expand to form lactiferous sinuses, sinus lactiferi. Occasionally, within the center of the nipple, the convergence of several lactiferous sinuses creates a common lactiferous sinus, sinus lactiferus communis, into which individual ducts empty. The presence of a common lactiferous sinus predisposes patients to lactational mastitis (inflammation of the breast lobes) more frequently than when the lactiferous ducts remain separate at the tip of the nipple.

The lactiferous ducts branch dichotomously, forming the lobules of the mammary gland, lobuli glandulae mammariae. In a non-functioning mammary gland, terminal structures such as alveoli are either absent or poorly developed. During pregnancy, the excretory ducts undergo intensive elongation and branching, generating a vast number of alveoli. In late pregnancy, these structures accumulate a secretion rich in Proteins and low in fats (colostrum). A few days postpartum, the secretory Cells (lactocytes) of the alveoli transition from producing colostrum to secreting mature milk, which has a higher fat content and lower protein concentration.

Connective tissue septa are located between the lobes of the mammary gland; these continue into the surrounding adipose tissue and anchor the gland to the fascia of the pectoralis major muscle, the skin, and the clavicle. These connective strands form the suspensory ligaments of the breast, ligamenta suspensoria mammariae. Infiltration of these ligaments by malignant tumors gives rise to characteristic cutaneous dimpling and skin symptoms.

The nipple of the mammary gland appears as a pigmented elevation bearing the openings of the lactiferous ducts—the lactiferous pores, ostia papillaria. The nipple is surrounded by the areola, areola mammae, which contains the openings of areolar (sebaceous and sweat) glands, glandulae areolares. The dermis of the nipple and areola projects deeply into the epidermis, forming branching dermal papillae rich in nerve endings. Numerous myocytes cluster around the lactiferous ducts at the Base of the nipple, forming a specialized sphincter. The contraction of radially arranged myocytes causes the nipple to erect during infant feeding.

There are three primary nipple shapes: cylindrical, pyriform, and conical. Feeding proceeds normally with the first two shapes, whereas the conical shape can create difficulties for the infant in latching onto the nipple properly. This necessitates prenatal nipple preparation, a practice taught to expectant mothers in antenatal clinics.

Blood supply to the mammary gland is provided by Branches of the internal thoracic artery, a. thoracica interna, the lateral thoracic artery, a. thoracica lateralis, and the III–VII intercostal Arteries, aa. intercostales III–VII. Venous drainage is facilitated by corresponding Veins.

Lymphatic drainage. The Lymphatic vessels of the mammary gland are arranged in multiple tiers. The most superficial network, the subareolar lymphatic plexus, lies just beneath the base of the nipple. Deeper, within the confines of the areola, is the superficial areolar plexus, beneath which lies the deep areolar plexus. Within the substance of the gland, a network of lymphatic capillaries forms around each lobule, from which small lymphatic vessels course along the lactiferous ducts toward the areolar plexuses. Lymph from the subareolar and deep areolar plexuses drains into the superficial areolar plexus, from which it flows in three principal directions: from the lateral portion of the gland to the axillary Lymph Nodes, from the central portion to the subclavian nodes, and from the medial portion to the parasternal (internal thoracic) lymph nodes.

In cases of breast Cancer, the medial region of the organ is the most unfavorable site for tumor localization because metastases immediately involve the lymph nodes of the anterior Mediastinum. From there, they disseminate via the bronchomediastinal or right lymphatic ducts. Malignant metastases reaching the axillary lymph nodes rapidly spread to the closely associated supraclavicular cervical nodes. Additionally, metastases from axillary nodes may travel along lymphatic vessels piercing the pectoralis Major and minor Muscles to reach the apical axillary and upper thoracic nodes. Consequently, surgical management of breast cancer typically involves radical mastectomy—removal of the mammary gland along with all axillary lymph nodes, the surrounding adipose tissue, and the pectoralis major and minor muscles.

The Lymphatic system of the mammary gland undergoes structural changes throughout a woman's lifespan, across various Phases of the Menstrual cycle, and in response to pregnancy and lactation.

Innervation. Sensory nerve fibers are supplied to the gland by the III–VII intercostal nerves, the medial and lateral pectoral nerves (from the Brachial Plexus), and the supraclavicular nerves (from the Cervical plexus). These nerves also convey postganglionic sympathetic fibers originating from the thoracic ganglia of the Sympathetic trunk.