Normal anatomy of mammary glands

Dairy, or breast, iron is a paired organ and is located on the front chest wall. The base of the breast is attached to the sternum, covers the edge of the pectoral muscles and reaches the anterior axillary line. The shape of the mammary gland is due to the race of the woman, age and constitutional features. The size and shape of the breast can vary widely.

The normal volume of the breast is 200-300 cm3. The smaller it is, the more stable the shape of the gland. The place of attachment of the breast to the chest in height can be located from 2 to 6 ribs (the diameter of the attachment site varies from 12 to 15 cm); on the width - from the edge of the sternum to the anterior axillary (axillary) line. In profile 2/3 heights are occupied by a straight or slightly concave nasal segment, the lower third by a convex subsatcerial segment. The skin fold, formed between the lower segment of the gland and the anterior thoracic wall, forms the lower border of the organ.

The central part of the front surface of the breast is occupied by the nipple, which forms a cylindrical or conical protuberance. The nipple consists of epithelial and muscle tissue. In the central part of it pass the terminal sections of the excretory mammary ducts. The top of the nipple is intersected by grooves in which there are 15 to 25 small holes in the milk ducts. The outer part of the nipple is formed mainly by skin structures, inside of which there are both radial and circular muscle fibers. The reduction or relaxation of the muscular structures of the nipple and areola causes physiological changes in the state of the nipple and the terminal portion of the milk ducts.

A small pigmented area of the skin (from 4 to 5 cm in diameter) around the nipple is called the areola. On the areola are numerous elevations, tubercles, which are sweat glands. Subcutaneous muscle fibers form an areolar (okolososkovuyu) muscle. Together with the nipple, the areola is pointed slightly upwards.

The skin of the breast is thin and mobile. It easily glides over the gland and gathers into folds. In the nipple and areola, the skin is especially thin. There is no layer of subcutaneous tissue.

The body of the breast is a soft glandular organ consisting of adipose, glandular and connective tissue, and is located under the skin in a fascial case formed by cleaved leaves of the superficial fascia.

Fatty tissue intimately covers the body of the breast, forming the anterior and posterior layers. The anterior (subcutaneous or ferruginous) is interrupted in the pozadioreolar region, where the final sections of the milk ducts pass. Fatty fatty tissue is located in the form of separate clusters, which under the influence of the processes of involution are formed into fatty segments.

The connective tissue structures of the mammary gland are represented by their own capsule (anterior and posterior sheets of the split fascia), departing from it by coarse collagen fibers in the form of Cooper ligaments, a gentle fibrillar tissue located between the glandular elements and the structures that make up the wall of the milk ducts.

In the anterior sections of the Cooper ligament connect the body of the breast to the deep layers of the dermis, in the posterior sections attach to the fascial chest muscle case. Cooper ligaments that go deep into the gland cover, as a capsule, fat tissue, forming a fat lobule. The place where Cooper's ligament is attached to the glandular structures is called the Duret's crest.

The function of the mammary gland is in the production and secretion of milk. Functioning fibroglandular tissue of the breast is called the parenchyma.

The parenchyma of the mammary gland is represented by complex alveolar-tubular glands harvested into small lobules, from which the lobes form. In accordance with the general dimensions of the mammary gland, the size of the glandular lobes varies from 1-2 cm in length and 1.5-2.0 cm in width (small glands), up to 5-6 cm in length and 3-4 cm in width (large glands). The number of lobes (as well as their sizes) depends on the size of the mammary glands and ranges from 6-8 (small glands) to 20-24 (large glands). The shares are located radially in relation to the nipple and can be superimposed one on the other. The glandular lobule and glandular lobe does not have an external capsule and is not so much anatomical as a functional unit of the mammary gland. From each glandular lobule departs a terminal lacteal duct. During pregnancy, within the glandular lobules, numerous microscopic vesicles - the acini - form at the ends of the milk ducts. Acinus produces milk during lactation and atrophies or disappears after the end of breastfeeding. The bulk of the glandular tissue is in the upper outer quadrant and in the posterior parts of the breast. Often, the glandular tissue is located in the axillary region, forming an axillary lobe. Between the glandular structures of the parenchyma is a friable and tender connective tissue. The complex of glandular and connective tissue is united by the term fibroglandular tissue.

A complex network of milky ducts connects the acini (during pregnancy and lactation), glandular lobules and lobes of the breast, forming galactophors of 1-3 orders of magnitude. The dimensions of the terminal (terminal) milky ducts that extend from each lobule (1st order galactophores) and the lobar ducts (2 nd order galactophors) in the hormone-calm mammary gland do not exceed 2 mm in diameter. Behind the areola are the main, largest channels with a diameter of up to 3 mm (galactophors of the third order). These main ducts make a bend before forming an opening on the surface of the nipple in the form of holes, forming a milky sinus. The milky sinus acts as a reservoir during lactation. The outer part of the milky duct is formed by connective tissue structures. The internal part of the duct consists of a single-layered cubic epithelium located on the basal membrane. As a result of the cyclic action of sex hormones, the epithelial cells produce and then reabsorb the secret of the milk ducts in the non-lactating mammary gland. During lactation in the lumen of the ducts there is milk.

The mammary gland is supplied with blood mainly by the branches of the external thoracic and subclavian arteries and, to a lesser extent, by the intercostal arteries. Arteries form a wide network of anastomoses behind the areola. Deep veins accompany the same-named arteries. Venous outflow is carried out through a surface and deep network. Venous anastomoses can form a fancy pattern around the base of the areola.

The lymphatic system of the mammary gland consists of intra-organ lymphatic capillaries, extra-organ outflow vessels and regional lymph nodes. A large number of lymphatic vessels is under the skin in the form of a superficial lymphatic network. Lymphatic vessels in the interlobular space form a deep network of lymphatic vessels in the form of lacunae and plexuses between the glandular segments and the milk ducts. There are no lymphatic vessels in the glandular lobules themselves. Intraorganic and extraorganic lymphatic vessels and groups of lymph nodes can be joined together in two ways. In the first case, the connection is made directly between the lymphatic vessels and regional lymph nodes, and in the second - this connection occurs with the mandatory involvement of the subareolar lymphatic network. Such a complex system of lymphatic drainage of the breast is one of the causes of specific damage to various regional lymph nodes.

Depending on the quadrant of the lesion of the breast tissue, various groups of regional lymph nodes are involved in the tumor process. When the tumor is localized in the upper outer quadrant, the front and central axillary regional lymph nodes are most often affected. When a malignant tumor is localized in the upper inner quadrant, early metastases in the axillary lymph nodes of the opposite side and also in the lymph nodes of the anterior mediastin can occur quite early.

Innervation of the breast is carried out by nerve trunks located along the skin and inside the glandular tissue. Surface sensitivity is due to the pectoral, brachial and intercostal nerve trunks.

Physiology of the breast

From birth to old age, the mammary glands undergo complex physiological changes. Until the end of the early puberty period 7-8 years (1st stage), there are no special structural changes. 2 stage pubertal period (8-9 years) is characterized by a one-sided increase in the mammary gland of the girl in the back of the nipple. This is the stage of physiological asymmetric hypertrophy of the mammary glands. By the age of 10-11, the size of both glands is compared. In the third stage of the pubertal period, there is a further increase in the size of the breast not only behind the nipple, but also along its periphery (12-13 years). In 4 stages the mammary gland acquires a conical shape. At the age of 15, the formation of the mammary gland is completed (stage 5). During this period, the mammary gland acquires a more rounded shape.

The beginning of the formation of the breast (telarhe) occurs long before the first menstruation (menarche). With the onset of menstruation (from 12-14 years) in the mammary glands under the influence of estrogens, cyclical morphofunctional changes begin to occur. 1-10 day - tubuloacinosis involution, 11-16 day - galactophore proliferation, hypervascularization of connective tissue, 17-28 day - acinous proliferation, glandular hyperplasia and gradual limitation of vascularization of connective tissue. The surface blood flow prevails, sometimes the painful tension of the gland is noted. By the end of the cycle, a gradual increase in the volume of the mammary glands occurs by 20%.

The processes of involution begin in the mammary gland after the termination of the first pregnancy. Especially violently, the involution of the mammary glands takes place in the pre-menopausal period and in menopause.

Periods of age-related breast reconstruction include:

• 1. Period - gradual loss of glandular structures of the breast (35-40 years);
• 2. Period - thickening of the cylindrical duct epithelium, associated with a decrease in the number of myoepithelial cells, irregular thickening of the basement membrane and especially fibrous restructuring of the connective tissue (40-45 years);
• 3. Period - dilation, and sometimes cystic enlargement of some of the milk ducts trapped by fibrous tissue (45-50 years);
• 4. Period - slow obliteration of the milk ducts, as well as vessels of small caliber (after 50 years); During this period, in parallel with the sclerosis of connective tissue, excessive formation of adipose tissue occurs. Involute processes of the mammary glands are non-simultaneous. It is always possible to note the predominance of a particular process.

[1], [2], [3], [4]