Anatomy of the breast

1
Anatomy of the breast

• 3 types of tissue glandular, fibrous, adipose
• glandular tissue forms lobes (15-20 per breast)
• lobes made of alveoli
• epithelial cells line lumen, synth. milk
• myoepithelial cells surround epith. cells are
  contractile
• alveoli are vascularized
• alveoli open into lactiferous ducts
• ducts gt lactiferous sinus

2
Biochemistry of milk

• composition varies with time postpartum
• 1st week gt colostrum
• yellowish, sticky secretion
• small volume (40 mls / day)
• contains more protein, fat soluble vitamins,
  antibodies than milk produced later
• contains less fat and lactose
• subsequent milk production
• antibodies decreases
• protein content decreases
• fat content increases, as does lactose
• importance of lactose converted to galactose
  essential for myelin formation in nervous tissue

3
Advantages of breast milk

• antibodies
• less sugar than infant formulas
• contains amino acids, fatty acids, cholesterol
  not found in formulas
• growth factors (epidermal growth factor)
• GnRH
• delta sleep inducing peptide
• less atherosclerosis, hypertension, allergies,
  childhood diabetes, ear infections, SIDS, obesity
  in breast fed babies
• disadvantages of breast milk
• harmful substances ingested by mother can pass to
  baby

4
Initiation of milk secretion

• breasts are adequately developed to begin milk
  secretion during 4th month
• doesnt begin until after parturition (even
  though prolactin is high)
• E and P inhibit prolactin action in mammary
  tissue
• prolactin will fall slowly after parturition if
  suckling does not occur (over 3-4 weeks)
• when suckling occurs, sensory nerves in nipple
  convey info to spinal cord gt brainstem gt hypoth
• results (data from rat studies)
• reduction in dopamine into portal vessels
• increased release of prolactin releasing factor
  (vasoactive intestinal peptide, VIP)
• increased VIP gene expression in PVN

5
Milk secretion, contd.

• amount of prolactin released depends on strength
  and duration of suckling (twin studies)
• prolactin release during one episode stimulates
  milk production for next
• prolactin is biggest determining factor re milk
  secretion
• secretion can be boosted by administering
  thyrotropin releasing hormone (TRH or TRF)

6
Milk ejection reflex

• milk must be transported from lumen of alveolus
  to nipple
• transport induced by milk ejection reflex (MER)
• sensory information due to suckling travels via
  spinal cord, brainstem to hypoth
• activates oxytocin neurons in hypoth (both
  synthesis and secretion)
• oxytocin reaches alveoli gt activates receptors on
  myoepithelial cells gt contraction
• milk ejected thru nipple
• NOTE ejection is not due to sudden increase in
  milk secretion into alveolus
• MER can become a conditioned reflex in response
  to other stimuli assoc with suckling (not true of
  prolactin)

7
Milk ejection, contd.

• MER can be inhibited by physical, psychological
  stress
• mechanism unclear
• inhibition of oxytocin release?
• activ. of sympathetic nervous system gt
  vasoconstriction gt limits access of oxytocin
• suppression of lactation
• administration of sex steroids
• administration of bromocriptine (dopamine
  receptor agonist)