Breast refers to an endocrine gland positioned on the front of the chest, comprising of glandular acini which is covered by cells which contain the features of securing milk under hormones influence. Breast in the adult women is comprised of adipose tissues, connective tissue, and glandular tissues which determine the organ texture, shape and size. At the breast apex is mammary areola which is a skin area that is pigmented with improved sebaceous glands which have the role of making nipple elastic and soft. This paper analyses the anatomy of human breast.
Size, Dimensions, Shape
The shape and size of women breast differ considerably where by some women contain a large volume of breast tissue and thus bigger breasts compared to others. In most cases human breast is predominantly circular, apart from slight oblong part that further extends into axillary area. However, women breasts are hardly symmetrical. Normally one breast is slightly large, lower, or differently shaped. The characteristics and size of the nipple also differ greatly from one person to another. Nipples can be cylindrical, round or flat in shape. In addition the breast appearance and shape undergo various modifications as a woman ages.
Surface Anatomy/ Landmarks
The areole and nipple epidermis is highly pigmented and a bit wrinkled. The nipple skin has various apocrine and sebaceous sweat glands and comparatively little hair. The nipple base has 15 to 25 milk duct that enters in it, which dilate to create the milk sinuses. The sinuses terminate a little below the surface of the nipple in cone-shaped ampullae. The nipple is surrounded by circular areola and differes in diameter between 15 and 60 mm. Its skin has lanigo montgomery’s glands, sebaceous glands,, sweat glansd, and lanugo hair, that are improved sebaceous gland with small milk ducts which opens into the tubercles of morgagni in the areola epidermis.
Human breast is positioned on the anterior wall of the chest covering pectoralis minor and major muscles. The breast inferior border is at 6th rib, superior border is at 2nd rib, medial border is at sternum edge, while lateral border is at the mid axillary line. The breast deep margin is positioned at fascia major muscle of pectoralis. Normally, breast tissues extend into axilla.
Parts/ Divisions/ Layers/ Composition
Human breast has mammary ridges or milk line which runs between inguinal and axilla region where tissue of breast might be formed. Sonographically breast has got six identified tissues layers. They include chest wall, skin layer, muscle layer, premammary layer, retromammary layer and mammary layer. The skin layer consists of epidermal cells, hair follicles, and sebaceous glands. It covers the breast tissue subcutaneous layer1. Premammary layer has varied degrees of fat associated to pregnancy, obesity and age. Mammary layer is the only layer which has glandular tissues, stromal and epithelia tissues and contains 15-20 glandular tissues lobes organized in a radial fashion. Retromammary layer is situated posterial to the layer of mammary, and has different fat levels based on age, pregnancy, and obesity and deep fascia in the retrommary space.
The breast has ligaments and tissue that offer its support and provide its shape. It also has layers of fats which are located right under the skin, whose main role is protected and surround the milk making lobules. It also contains muscle which links breast ribs, upper arm and collarbone.
Surgical Access to Organ
The breast surgical access can be done for breast reconstruction due to various health conditions including cancer. Breast conserving surgery (BCS) is the proposed optional approach for majority of breast cancer patients in early stage.
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BCS comprised of local breast tissues resection regarded as segmental mastectomy. Brest reconstruction surgery may also be done after the BCS, with options such as implant reconstruction or autologous tissues. In case IBR is conducted nipple sparing or skin sparing mastectomy are probable.
Blood Supply/ Drainage
The breast blood supply is a rich anastomotic system resulting from the intercostal arteries, internal thoracic, and axillary. The biggest vessels originated from artery of the internal thoracic, the pricking branches that pierce the wall of the chest that is next to the sternal edge in the first four intercostal spaces. The four axillary artery branches include subscapular, superior thoracic, lateral thoracic and the acromiothoracic pectoral branch. The arteries are accompanied by the matching veins.
The breast is innervated by the anterior and lateral cutaneous branches of the 2nd to 6th intercostal nerves. The branches of lateral cutaneous pierce the intercostal muscles and the profound fascia in the midaxillary line and assume an inferomedial course. The 2nd lateral cutaneous brunch ends in the breast axillary tail. The 3rd to the 6th lateral cutaneous branches stretch on the serratus anterios surface for 3-5 cm. They then divide at the pectoral muscle border into superficial and deep branch. The course of deep branch within or below the pectrol fascia to the midclavicualr line, where make an almost 90o turn to enter the glands releasing a number of branches. The superficial branches stretch in the subcutaneous tissues and ends in the lateral breast skin. The anterior cutaneous branches innervate the breast medial portion. They divide into a medial and lateral branch after penetrating the fascia. The lateral branch separate again various small branches as the medial branch transverse the sternum lateral border, that assume an inferolateral course over he subcutaneous tissue. They turn to be continuously superficial on their way and end at the edge or areolar or in the skin of the breast. The superclavicular nerves end in the superior breast part in the skin.
The axillary lymph nodes are separated into five not entirely unique anatomical groups and differ in quantity from 20 to 30. They move away from the apical nodes and join at the subclavian trunk. This trunk normally directly drain into the thoracic duct on the left side,, while subclavian truck on the right side might empty into a joint right lymphatic duct or directly into the junction of jugulosubclavian. A small number of efferent channels normally directly attain the inferior nodes of deep cervical.
Histology/ Microscopic Anatomy
Human breast contains nipple which is covered by squamous epithelium that are pigmented. It also has ducts which dilate to create lactiferous sinus under the nipple. Duct basement membrane is continuous with skin basement membrane. It also has keratin producing epidermis squamous cells which spread for 1-2mm in major duct. Human breast microscopy anatomy comprises of skin appendages which comprises of Montgomery tubercles, eccrine sweat ducts and glands, and apocrine sweat ducts and glands. There are also large systems of duct comprising of 15 to 20 major systems of duct which are empty at the nipple. These ducts ramify to an extent of creating multiple round acinis (TDLUs). The systems of ductal differ considerably in extent and size and they do overlap in most cases. Finally there is lobules which are created after branching of terminal ducts into multiple round acini. Lobulocentric has an architecture that contains duct enclosed by multiple acini. TDLU can develop with acini coalescene to create structures similar to ducts, with about half of glandular tissues situated at the outer upper quadrant.
Embryology; Developmental Anatomy
Human breast starts its development at the 5th week of fetus where an ectodermal milk streak grows along the truck on each side to the groin from axilla. From birth up to puberty, human breast contains lactiferous ducts. The ducts beings to multiply where they are terminated from solid cells masses. During pregnancy there is appearance of secreting alveoli where by in early weeks of pregnancy lobular proliferation and ductal sprouting happen, with increases oreolar pigmentation and increased nipple. In the last pregnancy days, colostrum is secreted which is later replaced by milk. At menopause, the breast atrophies glandular tissues turns to be less cellular and level of collegen reduces.
Normal and Pathologic Variants
Human breast can vary in size and shape based on person age, breast tissue volume, weight gain and loss, family history, lactation and pregnancies history, elasticity and thickness of the breast skin, menopause and level of progesterone and estrogen hormones influence. The pathological variation can be caused by various conditions for instance congenital hypoplasia is condition typified by breast underdevelopment. The condition is related to turner syndrome, Poland syndrome, ulnar-mammary syndrome and congenital adrenal hyperplasia. Others include amastia which is a rare congenital illness typified by the breast tissues, areola and nipple absence. Amazia is another condition which is identified by glandular parenchyma absence in either both or one breast. Supernumarary nipple is a minor malformation characterized by accessory nipple.
Normal Organ Physiology
There are no apparent structural or functional variations between female and male breast before puberty. During this time both female and male breast contains multiple rudimentary ducts organized converging and circumferentially towards the nipple. They are also poorly developed and the blind end of every rudimentary duct, though possibly secretory acini. With puberty onset, the female breast experiences function and morphology changes due to distinctive response of the breast to different normal influences of hormones that include progesterone and estrogen.