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The Breast

a. Situation and deep relationsb. Structurec. Blood supplyd. Nerve supplye. Lymphatic drainagef. Developmentg. Human milk

1. Situation and deep relationsa. Lies in superficial fascia of the pectoral region (except for tail)b. Axillary tail of Spence pierces the deep fascia & lies in the deep

fasciac. Extent

i. Vertically; 2nd to 6th ribsii. Horizontally; lateral border of sternum to the mid-axillary

lined. Deep relations

i. Pectoral fascia: the deep fascia which the breast lies onii. Muscles which lies deeper to the breast

1. Pectoralis major2. Serratus anterior3. External oblique

iii. Retro mammary space: loose areolar tissue which separates the breast from the pectoral fascia

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2. Structure

a. The skini. Nipple

1. Conical projection2. Just below the centre of the breast3. At the level of 4th intercostals space4. Pierced by 15 to 20 lactiferous ducts5. Contains circular smooth muscles : make the nipple

stiff6. Contains longitudinal smooth muscles : make the

nipple flatten7. Has few modified sweat & sebaceous glands

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8. Rich in nerve supply9. Has many sensory end organs at the termination of

nerve fibres10.Devoid of hair

ii. Areola1. Skin surrounding the base of the nipple2. Pigmented circular area3. Rich in modified sebaceous glands (particularly at its

outer margin)a. Become large during pregnancy & lactation

(raised tubercles of Montgomery)b. Produce oily secretions

i. Lubricate nipple & areolaii. Prevent them from being cracking during

lactation4. Contain some sweat glands & accessory mammary

glands5. Devoid of hair

b. The parenchymai. glandular tissue

ii. 15 to 20 lobesiii. each lobe is a cluster of alveoliiv. drained by a lactiferous ductv. lactiferous ducts converge towards the nipple & open on it

vi. each duct has a dilation called a lactiferous sinus near its termination

vii. Histology of parenchyma1. Alveolar epithelium

a. In resting phase : simple cuboidal epitheliumb. During lactation :

i. Simple columnar epitheliumii. Distended alveoli may appear cuboidal due

to stretching (but much larger than those in the resting phase)

2. Smaller ducts : simple columnar epithelium

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3. Larger ducts : stratified columnar epithelium (2 or more layers)

4. Terminal parts of lactiferous ducts : stratified squamous keratinized epithelium

5. Myoepitheliocytesa. Found around alveoli & ductsb. Lies between the epithelium & BMc. Facilitates the passage of milk from alveoli, into

& along the ducts

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c. The stromai. Fibrous stroma

1. Supporting framework of the gland2. Forms septa known as the suspensory ligaments of

Cooper3. Anchor the skin to the pectoral fascia

ii. Fatty stroma1. Main bulk of the gland2. Distributed all over the breast;3. except beneath the areola & nipple

3. Blood supplya. Arterial supply : arteries converge on the breast & are

distributed from the anterior surface; the posterior surface is relatively avascular

i. Internal thoracic artery : through its perforating branchesii. Some branches of axillary artery;

1. Lateral thoracic artery2. Superior thoracic artery3. Acromiothoracic artery (thoracoacromial artery)

iii. Lateral branches of the posterior intercostal arteries

b. Venous drainage : veins follow arteries; first converge towards the base of the nipple & form an anastomotic venous circle, from where veins run in superficial & deep sets

i. The superficial veins drain into;1. Internal thoracic vein2. Superficial veins of the lower part of the neck

ii. The deep veins drain into;1. Internal thoracic vein2. Axillary vein3. posterior intercostal veins

4. Nerve supply

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a. Anterior & lateral cutaneous branches of the 4th to 6th intercostal nerves

b. Convey sensory fibres to the skinc. Convey autonomic fibres to smooth muscle & to blood vesselsd. Nerves do not control the secretion of milk (controlled by

prolactin hormone)5. Lymphatic drainage

a. Lymph nodesi. Axillary lymph nodes – 75%

1. Anterior(pectoral) group – chiefly2. Posterior group3. Lateral group4. Central group5. Apical group

ii. Internal mammary (parasternal) nodes – 20%© Garaka Rabel – 2009

directly or directly or directly or directly or directly or directly or

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iii. Posterior intercostal nodes – 5%iv. Some lymph also reaches;

1. Supraclavicular nodes2. Cephalic(deltopectoral) node3. Subdiaphragmatic lymph plexus4. Subperitoneal lymph plexus

b. Lymphatic vesselsi. Superficial lymphatics

1. Drain skin, except for the nipple & areola2. Pass radially to surrounding lymph nodes;

a. Axillary lymph nodesb. Internal mammary (parasternal) lymph nodesc. Supraclavicular lymph nodesd. Cephalic(deltopectoral) lymph node

ii. Deep lymphatics1. Drain parenchyma, nipple & areola

iii. Important lymphatic structures:1.

2. Internal mammary nodes drain lymph from both inner & outer halves of the breast

3. Subareolar lymph plexus of Sappy (a lymphatic plexus deep to areola) drain into anterior group of axillary lymph nodes

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5%

20%

75%

Axilla

Paraster Posterior

Supraclavic

Apical

LaterCentr

PosteriAnterior

Brea

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4. Lymphatic from deep surface pass through pectoralis major & clavipectoral fascia to reach;

a. Apical nodes &,b. Internal mammary nodes

5. Lymphatics from lower-inner quadrants may communicate with subdiaphragmatic & subperitoneal lymph plexuses, after crossing costal margin; then pierce anterior abdominal wall through upper part of linea alba

6. Development

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a. Mammary ridge (milk line or line of Schultz)i. Extends from axilla to groin

ii. Appears during 4th week of intrauterine lifeiii. In human beings it disappears, persisting only in pectoral

regioniv. Breast develops from ectodermal thickening of persisting

part of this ridgev. Gland is ectodermal & stroma is mesodermal in origin

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b. Formation of mammary glandi. Persisting part of the mammary ridge is first converted into

a mammary pitii. Secondary buds(15-20) grow down from floor of the pit

iii. These buds divide & subdivide to form lobesiv. Entire solid system is canalized laterv. At birth, nipple is everted at the original pit

c. Growth of mammary gland, at puberty caused by;i. Oestrogen

ii. Progesterone – stimulates development of secretary alveolid. Developmental anomalies

i. Amastia – absence of breastii. Athelia – absence of nipple

iii. Polymastia – supernumerary breastsiv. Polythelia – supernumerary nipplesv. Gynaecomastia – development of breasts in a male (occurs

in Klinefelter’s syndrome)

7. Human milka. Contents

i. Water – 88%ii. Lactose – 7%

iii. Fat – 4%iv. Proteins – 1% (caseins, lactalbumin)v. Ions (Ca2+, PO4

3-, Na+, K+, Cl- )vi. Vitamins

vii. Antibodies (of IgA variety)b. Colostrum

i. Milk secreted in later part of pregnancy & few days after parturition

ii. Contain many immunoglobulinsiii. Rich in fat & poor in nutrientsiv. Fat contains in colostral corpuscles

c. “Witch’s milk”i. Milk secreted by infant’s breast

ii. During first 1 or 2 weeks after birthiii. Under the influence of maternal oestrogen

d. Lactation

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i. Active in mothers, for about 5-6 months after parturitionii. Thereafter, diminishes progressively

iii. Thus, the infant has to be weaned by about 9 months of age

© Garaka Rabel – 2009