Anatomy Of Upper Limb And Thorax By Vishram Singh Pdf Download
Tyrell Baskerville
- Includes new chapters on surface anatomy in each section of upper limb and thorax
- Addition of many new line and half-tone diagrams, radiographs, CT scans and MRI images, tables, flowcharts to facilitate greater retention of knowledge
The mammary gland is a highly evolved and specialized organ developing on each side of the anterior chest wall. This organ's primary function is to secrete milk. Though the gland is present in both sexes, it is well-developed in females but rudimentary in males. The mammary gland is a vital accessory organ in the female reproductive system.
The mammary gland is classified as apocrine. Thus, the secretory cells' apical segment and a portion of their cytoplasm become part of the secretion. The mammary gland usually weighs between 500 and 1000 grams each. The organ is hemispherical in young adult females but becomes pendulous later in life. This article discusses the anatomy, function, and clinical importance of the mammary gland.
The mammary gland is situated in the pectoral region in the superficial fascia. However, a segment called the "axillary tail of Spence" pierces the deep fascia and lies in the axilla up to the 3rd rib level. The mammary gland extends vertically from the 2nd to the 6th rib. Horizontally, it spreads from the lateral sternal border to the mid-axillary line.
Deep to the mammary gland tissue is the retromammary space, a loose connective-tissue plane that gives free mobility to the gland. Below the retromammary space is the pectoral fascia, which covers the pectoralis muscle. The serratus anterior and external oblique are other muscles that lie deep in the mammary gland.
The skin consists of the nipple and areola. The nipple is a conical eminence situated in the 4th intercostal space (ICS). Piercing the nipple are 15 to 20 lactiferous ducts. The nipple contains richly innervated circular and longitudinal smooth muscle fibers, which make it erect upon stimulation. The nipple usually has no sweat glands, fat, or hairs.
The areola is the dark pinkish-brown area around the nipple. This area is rich in modified sebaceous glands (tubercles of Montgomery) during pregnancy and lactation. These modified glands produce oily secretions that prevent nipple and areolar cracking. Notably, the areola is devoid of fat and hair.
Glandular tissue is comprised of branching ducts and terminal secretory lobules. One lactiferous duct drains 15 to 20 lobes. These ducts enlarge to form the lactiferous sinus before they open separately into the nipple. Milk collects in the lactiferous sinuses and is released in response to the baby's suckling. The lactiferous ducts are arranged radially in the nipple. Hence, incisions in this area must be oriented radially to avoid cutting through multiple lactiferous ducts.
Fibrous stroma gives rise to septa called "suspensory ligaments of Cooper," which separate the lobes and suspend the mammary gland from the pectoral fascia. In patients with breast cancer, contraction of these ligaments causes breast rigidity and puckering of the overlying skin. In breast cancer, the Peau d'orange sign arises from lymphatic obstruction and subsequent cutaneous edema and fibrosis.
The mammary gland is best examined by dividing it into 4 quadrants, with vertical and horizontal imaginary lines passing through the nipple (see Image. Mammary Gland Quadrants). The regions are designated as the upper outer (UOQ), upper inner (UIQ), lower inner (LIQ), and lower outer (LOQ) quadrants.[1][2]
Breast development is minimal and comparable in both sexes until females reach puberty. Estrogen, progesterone, and growth hormone spurt during the pubertal phase and induce greater development in females than males. The smooth contour of female breasts is due to increased adipose tissue.
The female breasts further increase in size in early pregnancy, with estrogen and progesterone inducing parenchymal growth and ductal branching. Secretory alveoli and the surrounding connective tissue start developing at duct terminals. In the later stages of pregnancy, these alveoli are filled with milk under prolactin's influence. When lactation stops, the secretory alveoli shrink, decrease in number, and disappear. However, the mammary gland never returns to prepubertal form. After menopause, the breasts regress in size due to diminishing circulating estrogen levels.
Genetic and hormonal factors influence ectodermal cells to form the human breasts starting in the 4th week of embryonic life. Ectodermal thickenings, known as mammary ridges (milk ridge or milk line), emerge on the chest around the 4th intercostal space, giving rise to rudimentary mammary buds by the 5th week of gestation. These primary mammary buds extend downward, developing into secondary buds and intricate mammary lobules over the next 7 weeks. The breast stroma, fat, ligaments, nerves, arteries, veins, and lymphatics undergo development throughout the gestational period.
Beyond the 12th week, the secondary buds continue their growth, elongating and branching into 15 to 20 solid cords that differentiate into the lactiferous breast ducts and their branches. The ducts later canalize under the influence of maternal sex hormones, connecting the developing nipple to the expanding mammary lobules.
The fetal nipple is inverted but everts at birth due to the proliferation of its modified sebaceous glands (future Montgomery glands) and muscle tissue. Areolar pigmentation also increases at birth.[2]
Breast veins are divided into superficial and deep veins. Superficial veins commonly drain the central and peripheral breast areas. The central veins form a venous plexus known as the "circulus venosus of Haller." Blood flows from this venous network into the internal thoracic vein medially, lateral thoracic veins laterally, and the superficial neck veins superiorly. The deep breast veins drain into the internal thoracic, axillary, and posterior intercostal veins. Valves are typically absent in breast veins, and intramammary venous anastomoses are frequently observed.
Lymph from the breasts drains primarily toward the axillary and internal mammary groups, though a small amount also empties to nearby lymph nodes. These lymph nodes are clinically important, as they are common sites for breast cancer metastasis.[3][4]
The axillary lymph node group is the main breast drainage site, collecting 75% to 80% of lymph from the breasts. The pectoral group drains most of the lymph going to the axillary nodes. The remaining 20% to 25% of breast lymph drains to the internal mammary nodes.
The literature has reported vast differences in breast tissue innervation, especially in the areola and nipple. However, most agree that the anterior and lateral cutaneous branches innervate the mammary gland from the 2nd to 6th intercostal and supraclavicular nerves. These nerves form a plexus deep into the areola in the subdermal tissue and supply the nipple and areola.[5][6] The nipple and areola are highly sensitive to touch, and these sensations are carried mainly by the T4 spinal nerve dermatome.
The breast's nerve supply, particularly in the nipple and areolar areas, is the subject of recent studies. Innervation in these regions must be preserved during breast surgical reconstruction.[7][8][9]
The mammary gland is a modified sweat gland comprised of parenchymal and stromal tissues covered by skin. As previously mentioned, the nipple area becomes erect when stimulated due to its smooth muscle fibers. Besides these muscles, chest wall skeletal muscles are situated deep to the breasts.
The pectoralis muscle is the predominant skeletal muscle posterior to the mammary gland. The pectoral fascia covers this muscle. The pectoralis minor lies posterolateral to the pectoralis major. Other skeletal muscles deep into the breasts include the serratus anterior and external oblique.
The skeletal muscles in the mammary region are surgically important. Successful breast reconstruction and implantation require an intact pectoralis muscle.[10][11] Meanwhile, the muscle flap most frequently used for breast reconstruction is the latissimus dorsi.[12][13]
The mammary gland shows physiological variations in size, shape, contour, density, spacing, and volume. These variations depend on factors like age, height, weight, genetic composition, race, nourishment, and environment. Breast asymmetry is observed in 25% of females, with the size and shape differing in the same person.
Nipple inversion is also quite frequently seen in females. This condition can be physiological and correct spontaneously over time or during pregnancy. However, nipple inversion may also be an early indicator of underlying pathology.[14]
Surgery, ranging from lumpectomy to radical mastectomy, is the treatment of choice for breast lesions (See Image. Total Mastectomy). As mentioned earlier, breast malignancies can metastasize through the lymphatics (see Image. Cancer Metastasis Sites). Knowledge of the mammary glands' lymphatic drainage helps surgeons identify the affected lymph nodes before dissection.[15]
Recurrence is common, making adjuvant radiotherapy necessary after breast cancer surgery. Patients with a higher recurrence risk may also receive adjuvant chemotherapy, which may prolong their disease-free overall survival period. Hormonal therapy is helpful when breast tumors are estrogen- and progesterone-receptor-positive. Tamoxifen has been proven effective in estrogen-positive breast cancer patients.
The global rise in breast carcinoma cases has resulted in an increase in surgical mastectomy and demand for surgical breast reconstruction, breast implantation, and mammoplasty.[16][17] This trend has resulted in increased interest in understanding breast anatomy and developing new surgical breast treatments.[18][19][20]
Breast lesions may be benign or malignant. Most breast lesions are benign, but they have gained little attention because they are usually non-fatal.[21] Fibrocystic changes are the most common benign lesions, constituting almost 40% of all cases, even during the premenopausal years.
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