breast anatomy Flashcards
features of the breast
- Male and female breast tissue is the same at birth
- Normally it only functions in biological female
- The changes occur due to the activity of hormones around puberty
- The breasts are paired structures on the
anterior thoracic wall in the pectoral region. - Developmentally, breasts are part of the skin and
are modified sweat glands - The mammary gland is contained within the skin
what stimulates the growth of the breasts
- Stimulation by oestrogen, growth hormone and insulin like growth factor (IGF-1) cause the increase in size in females
- Male hormones prevent any further development
gross anatomy of the breast
anterior, medial, lateral, superior and inferior borders.
- Generally, overlie the 2nd- 6th ribs
- Anterior to the pectoral muscle
- Medial border – sternum
- Lateral border – anterior or mid axillary line
- Superior border – infraclavicular fossa
- Inferior border – mid sternum
what is the nipple surrounded by?
Nipple – surrounded by areola – pigmented
4 quadrants of the breast
- The breast is divided into 4 quadrants plus a central area around the nipple
- 1-3 o’clock – upper inner quadrant
- 3-6 o’clock – lower inner quadrant
- 6-9 o’clock – lower outer quadrant
- 9-12 o’clock - upper outer quadrant
what is the internal anatomy of the breast
- Internally there are 15-20 lobes
- They are separated by connective tissue and adipose tissue
- Within each lobe there are around 20-40
lobules containing clusters of alveolar glands - The alveolar glands produce milk
- Male breast tissue lacks these specialised lobules
- Milk passes from the alveolar gland to lactiferous ducts
- Lactiferous ducts open to the outside at the nipple
terminal ductal lobular unit
- The functional unit of the breast is the lobule
- Terminal ductal lobular unit (TDLU)
- Consists of 10-100 acini, that drain into the terminal duct.
- The terminal duct drains into larger ducts and finally into the main duct of the lobe (or segment), that drains into the nipple. The breast contains 15-20 lobes, that each contain 20-40
lobules.
ductal system
- Lined with epithelium
- Reduced friction for milk flow
- Middle myoepithelial cells aid in movement of milk
- Basement membrane outer layer of duct in contact with intralobular stroma
ligaments
- Suspensory ligaments from interlobular connective tissue to the dermis
- Cooper’s ligaments
- Give breast shape
- Not taut – movement
- Relax with age/time
- Breast ptosis
venous drainage
- Venous drainage of the breast is mainly by the axillary vein
- The subclavian, intercostal, and internal thoracic veins also aid in venous drainage.
- Connections between the intercostal veins and the vertebral plexus allow metastasis of cancer to bones and to the nervous system
nerve supply to the breast
thoracic intercostal nerve t3-5
supraclavicular nerve from cervical plexus
lymphatic drainage of the breast
- Originates from lobules to sub areolar plexus – Sappey’s Plexus
- 75% of lymph drainage to axillary nodes
- Drainage by 3 main routes
what are the 3 main lymphatic drainage routes
Axillary/Lateral
* Fed by Sappey’s plexus to pectoral group of axillary nodes
Internal Mammary
* From lateral and medial
* Passes through pectoralis major
* May lead across median plane to contralateral
breast
* Retromammary
* Posterior part of breast
- 75% of lymphatic drainage of breast goes to the axillary nodes
- The lymphatic drainage of the breast is of great importance in he spread of carcinoma
what are the 3 levels of the axillary lymph nodes
There are three levels of axillary lymph nodes:
* level I - bottom level, below the lower edge of
the pectoralis minor muscle
* level II - lies underneath/posterior the
pectoralis minor muscle
* level III - above/medial the pectoralis minor
muscle
* 75% of lymph drainage is to the axillary nodes
* This is important to understand as it explains
the spread of carcinoma
how does oestrogen promote an increase in breast size?
- formation of mass of tissue under areola
- Increase in size and pigmentation of areola
- Development of lobular ducts
breast development
- Breasts of parous women and those never pregnant are different
- Expansion of acini only occurs during pregnancy when preparing for lactation
- During menopause lobules of parous women involute to pre-pregnancy composition and become identical to nulliparous women
premenopausal physiology changes of the breast
Premenopausal
- hormone levels decrease, glandular tissue shrivels or involutes, fat levels increase
postmenopausal physiological changes of the breast
- HRT can cause glandular tissue levels to increase
- Weight loss can lead to prominence of glandular tissue due to the decrease in the amount of surrounding fatty tissue.
During follicular/proliferative phase of menstrual cycle
- Oestrogen levels increase vascularity of breast tissue and stimulate proliferation of ductal and acinar tissue
- Effect sustained during luteal/secretory phase
- Progesterone levels increase and contribute to breast changes
- Dilation of ducts and conversion of acinar cells to secretory cells
- Breast volume may increase by 10 – 30mL
Length of menstrual cycle does not allow
for complete regression of effects - Breast growth continues until approx. 35 years
pregnancy influences on the breast
- Breast remodels into milk- secreting organ
- Reaches ultimate mature developmental stage
- Increased oestrogen – lobules further differentiate
- Progesterone stimulates cells
lining alveoli to produce milk - Increased levels of prolactin- lactation
- Positive feedback
- Lactation
- Milk continuously secreted into alveolar lumen
- Stored until myoepithelial cells stimulated by
suckling – oxytocin – triggers let-down reflex
Post pregnancy on breast
Breast has capacity to regress to a resting stage after cessation of lactation and the undergoes same cycle of expansion and regression in subsequent pregnancies
