Lecture 24: Breast Flashcards
What are the 2 evolutionary functions of the breast
- nutrition of young through breastmilk
2. spacing of pregnancies: more chance of running away from predators with children that can walk
Describe the steps in derivation of the breast from
28days, 6wks, 12wk–> birth
Seen in males and females same tissue
- 28 days= Mammary/milk crests arise between the axilla and the groin
- 6 wks: breast development begins with the formation of mammary buds- milk crests regress to a small area
- 12wk to birth: Down growth of the dermis to form the 1’ breast bud
- Secondary buds develop from the 1’ as branches, (precursors to lactiferous ducts)
- 2ndary buds become canalised which is induced by placental steroids - E2 and P2.
- By birth: 15-20 ducts present
What is witch’s milk, how common is it to what age, and between the sexes
The colostrum-like secretion of babies at birth due to exposure to the placental and maternal hormones required for lactation
This is 5% of neonates -> 1.8% at 2mo. No bias between sexes
What is gynaecomastia, when can it be seen and does it have relation b cancer
Increased prominence of breast tissue due to estrogen exposure - seen in newborns, during puberty.
Men are at risk of breast cancer too- 25 in NZ/year
Describe the Internal structures of the Breast
- Adipose tissue of the pectoral fat pad which gives the texture and shape of the breast
- Cooper’s ligaments which support the breast - affected by age and pregnancy hormones
- 15-20 lobes made of milk secreting lobules (alveoli) which connect to a single lactiferous duct.
The ducts run towards the nipple and expand into the lactiferous sinus (for storage) opening onto the nipple for milk extraction
Describe the External structures of the Breast
Nipple:
- Raised or inverted cylindrical and pigmented structure. Nerves to the nipple crucial for neuroendocrine reflex for lactation
Areola:
- pigmented circle of tissue surrounding the nipple.
contains sebaceous glands which give granular texture but No hairs.
What is the main difference in breast structure between birth, puberty (&non lactating) and pregnancy - including some of the main hormones involved
- Birth: breast ducts don’t have alveoli, not much fat
- Puberty: alveoli develop under influence of E2.
- progressive menstrual cycles of E2 and P2 promote the growth of alveolar buds - premenstrual increased breast volume and tenderness
Breast tissue dominated by ductal system and fat
- Pregnancy:
- Hormones in pregnancy cause increased duct growing, branching and budding of alveoli.
- Breast weight increases 2-3x at term, 4x by breast feeding
Breast tissue dominated by Alveoli and then ducts
What are the hormones involved in developing the breast during pregnancy and what part is it affecting
- E2: mitogen essential for breast growth
- P2: induces side branching of lact ducts
- (placental) Prolactin: necessary for alveolar epithelium development + Casein and a-lactalbumin
- Insulin and cortisol: stimulate alveolar epithelial cell division
- Human Placental Lactogen: prolactin like hormone which decreases insulin sensitivity increasing glucose release for the fetus to use
What are the 4 steps involved in triggering lactation
- Infant suckling on the nipple
2a) .Reduced secretion of dopamine into portal blood (prolactin inhibitor)
b) Increased secretion of Vasoactive intestinal Peptide (VIP) from paraventricular nuclei in hypothalamus is increased. (prolactin stimulator) - Both factors act on lactotrophs in the ant pit to secrete prolactin
- Prolactin induces the production of milk proteins at the alveoli
Eg. (casein (milk protein) and a-lactalbumin (part of lactose making enzyme)
Why does lactation not occur until birth if prolactin is produced in large amounts in pregnancy but drops at birth as the placenta is taken away
The steroids, esp placental Progesterone and Estrogen (P4 and E2) inhibit breast responsiveness to prolactin prevents major milk development as well as ejection as it is a SM relaxant
What are the benefits of having a neuroendocrine reflex control of lactation and what stimulus causes more prolactin secretion
- Not constant milk production
- the level of prolactin correlates with the level of milk produced so baby regulates the milk intake to avoid overfeeding
The duration and extent of suckling correlate with prolactin secretion - two infants suckling = more prolactin
What is Milk ejection response/ let down response and what is the cause and types of stimuli
This is ejection of milk from the nipple (forceful) caused by oxytocin inducing contraction of cross hatched myoepithelial cells of alveoli, pushing milk into ducts
- Suckling stimulates the synthesis and secretion from post pituitary
- Stimulation of cervix
- Feeding cry of a baby
- Smell of new baby
How does lactation affect fertility- menstrual cycles
Prolactin suppresses secretion of FSH and LH via effect on kiss peptin neuron in hypothalamus
This leads to lactational amenorrhoea/ irregular menstrual cycles - therefore contraceptive (no ovulation) (but not reliable)
- Spacing of pregnancies!
What is the prevalence of supernumeroury Nipples/breasts and where are they usually found on the body
<6% of population
Breasts: Found along the line of embryonic milk crest.
Additional nipples: can occur on the breast or along the milk crest.
Lactiferous ducts can exit the breast at sites outside the nipple
