Editing Breast


Breast or mammary gland

* Modified apocrine sweat gland     whose primary purpose is to produce milk
* lies in the subcutaneous     tissue of the anterior thoracic wall.

== '''Embryology''' ==

* Begins to develop as early as     the 5th week - 'milk lines' form along a line from the axilla to the     inguinal region, of ectodermal origin
** Supernumerary nipples or      even glands may form along this line
* Distal aspect of milk lines     begin to disappear by week 9
* Ectoderm in pectoral region     invaginates into the surrounding mesoderm. These extensions eventually     epithelialize, branch and canalize, forming ducts which reach the nipple.

== '''Surface markings of base:''' ==

* Medial - sternal edge
* Superior - second rib
* Inferior - sixth rib
* Lateral - near the     midaxillary line


== '''Structure and functional anatomy:''' ==

* Composed of adipose tissue,     connective tissue and glandular tissue
* Glandular tissue is most     concentrated in the upper outer quadrant
* Breast parenchyma (glandular     tissue) is composed of lobes, which can be further divided into smaller     lobules
** The lobular units are made      up of acini within loose intralobular stroma
** The lobular units are      surrounded by denser interlobular stroma, containing blood vessels,      larger breast ducts, and fat
* Lactiferous ducts (15-20)     converge in a radial direction, each draining a lobule, and each opening     individually to the tip of the nipple.
** Each duct has a dilated      sinus at its terminal distal portion in/near the nipple.
** The ducts end in terminal      ductules or acini
*** Milk-forming glands of the       lactating breast
*** Form a 'lobular unit' or       'lobule' together with their small efferent ducts or ductules
* Nipple - projection just     below centre of breast, surrounded by an area of pigmented skin, the     areola. Nipple contains smooth muscle cells which can contract to cause     nipple erection.
* Areola contains sebaceous     glands, sweat glands and other areolar glands. Areolar glands form small     elevations (tubercles of Montgomery), particularly when they enlarge     during pregnancy.
* Strands of fibrous tissue,     forming the suspensory ligaments of Cooper, connect the dermis of the     overlying skin to the ducts of the breast and to the posterior fascia
** When tumour infiltrates      these strands, the skin is tethered to tumour, and dimpling or subtle      deformities of shape result
* The male breast resembles the     rudimentary female breast and has no lobules or alveoli. The small nipple     lies over the fourth intercostal space.
* Breast size varies greatly     from <100g to >2kg




== '''Relations:''' ==

* Superficial: Sub-dermal layer     of adipose tissue
* Deep:
** Superficial fascia (which is      an upward continuation of Scarpa's fascia in the abdomen) condenses      posteriorly to breast tissue to form a posterior capsule.
** Between capsule and the      pectoralis fascia lies the loose connective tissue of the retromammary      space, also called retromammary fat pad. Relatively avascular.
** Overlies pectoralis major,      overlapping onto serratus anterior and a small part of rectus      sheath/external oblique
* Lateral: axillary tail may     prolong towards axilla, usually in the subcutaneous fat rather than the     deep fascia going into the actual axilla

== '''Lymphatic drainage:''' ==

* Abundant lymphatics in the     breast parenchyma and dermis
* 'Sappey plexus' located under     the NAC. Lymph flows from skin to subareolare Sappey plexus, then into the     interlobular lymphatics of breast parenchyma
* Sentinel node location:
** 75% of breast lymph passes      to axillary lymph nodes, mainly to anterior nodes, some to posterior      nodes; direct drainage to central or apical nodes is possible.
** 25% to parasternal nodes      along the internal thoracic artery (5% sole pathway, 20% shared with      axilla)
* Can drain to posterior     intercostal nodes.
* Occasionally, can drain to     infraclavicular nodes in the deltopectoral groove
* Direct drainage from breast     to supraclavicular nodes is possible
* These minor pathways tend to     only convey lymph from breast when the major channels are obstructed by     malignant disease.

== '''Blood supply:''' ==

* Three sources:
** Branches of axillary artery
*** Derived mainly from lateral       thoracic artery, by branches that curl around the border of pectoralis       major, and by other branches that pierce the muscle.
*** Pectoral branch of the       thoracoacromial artery supplies the upper part of the breast.
** Internal thoracic artery      (a.k.a. internal mammary) also sends branches through the 2nd-5th      intercostal spaces beside the sternum (largest in second and third IC      spaces).
** Small perforating branches      also arise from the posterior intercostal arteries.
* Venous drainage is mainly by     deep veins that run with the main arteries to internal thoracic and     axillary veins. Some drainage to posterior intercostal veins provides a     link to the internal vertebral venous plexus veins - hence metastatic     spread to bone.
* There is also a circumareolar     venous plexus

== '''Nerve supply''' ==

* Overlying skin supplied by     cutaneous branches of intercostal nerves T4-6
* Sympathetic fibres to blood     vessels and glands
* Control of lactation is     hormonal

== '''Microscopic anatomy''' ==

* Three principal tissue types,     with the proportions varying with age, cycle, pregnancy and breastfeeding:
** Glandular epithelium
** Fibrous stroma and      supporting structures
** Adipose tissue
* Layers surrounding ducts,     from inside to outside the duct:
** Entire ductal system lined      by epithelial cells
*** Stratified squamous       epithelium near the nipple
*** Transition to cuboidal       epithelial cells in the lactiferous sinuses behind the nipple
** Epithelial cells surrounded      by specialised myoepithelial cells - have contractile properties and      serve to propel milk towards the nipple
** Then a continuous basement      membrane containing laminin, type IV collagen, and proteoglycans
*** This layer is the key       differentiation between invasive and in situ breast cancer - DCIS does       not breach it
** Stroma - where the      lymphatics and blood vessels are located


== '''Physiology''' ==

* Puberty
** Thelarche - onset of adult      breast development - ductal elongation, increase in the height of the      pithelium and an increase in stromal density
** Oestrogen from ovaries      results in formation of additional lobular units
* Post-pubertal mature
** Responsive to exogenous      hormones - cyclical stimulation. Late luteal (pre-menstrual) phase sees      accumulation of fluid and intra-lobular oedema, sometimes producing pain      and breast engorgement.
* Pregnancy
** Diminution of the fibrous      stroma
** Formation of new acini or      lobules (adenosis of pregnancy)
** More alveoli per lobule, and      lobular units differentiate into secretory units
* Childbirth
** Sudden loss of placental      hormones, combined with continued high levels of prolactin, triggers      lactation
** Expulsion of milk is under      hormonal control by oxytocin - contraction of periductal myoepithelial      cells, which do not appear to have any innervation. Occurs in response to      stimulation of the nipple.
* Menopause
** Involution and general      decrease in the epithelial elements of the resting breast
** Increased fat deposition,      diminished connective tissue, and the disappearance of lobular units
** HRT can prevent these      changes - retention of breast epithelium and stromal tissue with      persisting breast density

[[Category:Anatomy]]