11) The breast Flashcards
Describe the structure of a normal breast
Glandular & supporting fibrous tissue embedded within fatty matrix, together with blood vessels, lymphatics & nerves
Where is the location of mammary glands in the breast?
Subcutaneous tissue overlying pectoralis major & minor
Consist of 15-20 lobulated masses of tissues
Fibrous tissue connecting the lobes & adipose tissue between them
What is each lobe of the breast made up of?
Lobules of alveoli, blood vessels & lactiferous ducts
Alveoli - site of milk synthesis
Myoepithelial cells, smooth muscle cells responsible for milk let down surround the alveoli
What determines the size of the non-lactating breast?
The amount of fat surrounding the glandular tissue
Roughly circular body of breast rests in a bed that extends from:
Lateral sternal edge to midaxillary line
2nd rib to 6th rib
List the constituents of human milk in the first week after birth
Up to 40ml/day of Colostrum secreted
Colostrum contains less water soluble vitamins, fat & sugar than later milk but much more protein, fat soluble vitamins & immunoglobulins
Over the following 2-3 weeks, IgG & total protein declines, fat & sugar rise to produce mature milk
What constitutes mature human milk?
Mature milk is produced for as long as the baby suckles (from week 2/3 breastfeeding)
Energy value of 27MJ/litre, pH 7.0
Composition: 90% water, 7% Lactose, 2% Fat
Proteins: Lactoglobulin (maternal IgG), Lactalbumin, Minerals, Vitamins
How is milk produced in the lactating breast?
Synthesis of milk takes place in Alveolar cells
Fats: synthesised in SER, then membrane bound droplets towards lumen
Protein: Passes through Golgi, secreted by exocytosis
Sugar: Synthesised & secreted
What hormones control the growth & development of mammary tissues?
Birth, few lactiferous ducts are present, breast remains this way until puberty
Puberty, oestrogens cause ducts to sprout & branch, the ends form masses of cells, later become alveoli
With each menstrual cycle, changes in breast tissue with changes in oestrogen & progesterone levels
What happens to mammary tissue during pregnancy?
High progesterone:oestrogen ratio favours development of alveoli, but not secretion
Hypertrophy of ductular-lobular-alveolar system
Prominent lobules form
Alveolar cells differentiate to be capable of milk production from mid gestation
What happens to milk production if an infant does not suckle?
Birth, progesterone falls sharply, less sharp fall of oestrogen
Breast becomes responsive to prolactin secreted from anterior pituitary
If infant doesn’t suckle, prolactin levels fall
How does suckling help to maintain breast milk production?
Suckling initiates & maintains secretion by neuro-endocrine reflex by mechanically stimulating receptors in nipple
Impulses pass to brain stem & hypothalamus to reduce dopamine secretion & vaso-active intestinal peptide, promoting prolactin
Amount of milk produced before next feed depends on suckling stimulus
Milk continuously produced between feeds, accumulates in ducts, increases turgor of breast
How is milk ‘let down’ controlled by hormones?
Caused by dramatic increase in secretion of Oxytocin from posterior pituitary
Oxytocin causes myoepithelial cells surrounding alveoli to contract
Infants don’t suck from breast, must learn from bottle
As suckling causes release of oxytocin, suckling also important, keeps uterus clamped down on open placenta blood vessels
‘Let down’ reflex can be conditioned, often begins before baby reaches nipple
How is the cessation of lactation produced?
Lactation maintenance dependent on suckling, to promote prolactin & oxytocin to remove milk
Suckling stops, production of milk stops
Due to lower prolactin levels & turgor-induced damage to breast
A reduction in prolactin helps the cessation of lactation. What else does it do?
Prolactin secretion also reduces fertility
New pregnancy less likely until infant stops suckling
What are common breast diseases?
Inflammatory conditions
Benign epithelial lesions
Stromal tumours
Breast carcinoma
What are the differences between physiological & pathological changes of the breast?
Physiological - Changes or symptoms that come about due to normal breast physiology
Pathological - Changes or symptoms that come about due to underlying breast pathology
Name some physiological breast changes
Prepubertal breast - few lobules
Menarche (first cycle/onset of puberty) - Increased number lobules, increased volume of interlobular stroma
Menstrual cycle - Follicular phase - lobules inactive, After ovulation - cell proliferation & stromal oedema, Menstruation - Decrease in size of lobules
What physiological breast changes take place during pregnancy?
Increase in size & number of follicles
Decrease in stroma
Secretory changes
Cessation of lactation - Atrophy of lobules but not to former levels
What physiological breast changes take pace with increasing age?
Terminal duct lobular units (TDLUs) decrease in number & size
Interlobular stroma replaced by adipose tissue (mammograms easier to interpret)
Name some pathological breast changes that take place
Disorders of development - Milk line remnants (3rd nipples). accessory axillary breast tissue
Inflammatory conditions - Acute mastitis, duct ectasia, fat necrosis
Benign epithelial lesions - Fibrocystic change, epithelial hyperplasia, papilloma
Stromal tumours - Fibroadenoma, phyllodes tumours, lipoma, hamartoma
Gynaecomastia
Breast carcinoma
