Lactation

Question 1

What are the mammary glands?

Answer 1

Exocrine - modified sweat glands

Embedded in breasts, ~15-20 lobulated masses of tissue with fibrous & adipose tissue in between

Alveoli (same as acini in sweat glands) + blood vessels + lactiferous ducts

Question 2

How do the mammary glands change during pregnancy and after birth?

Answer 2

At birth: only a few ducts are present

Puberty: ducts begin to sprout and branch

Changes in oestrogen & progesterone in the menstrual cycle change the size of the breasts

Pregnancy:

• placenta secretes oestrogen & progesterone —> change in breast tissue size (growth but not secretion)
• hypertrophy of the ductular-lobular-alveolar system —> prominent lobules form
• alveolar cells differentiate to become capable of milk production (mid gestation)

After birth:

• Immediately = 40ml/day of colostrum (less water, fat, & sugar; more proteins, esp. immunoglobulins to confer passive immunity to baby)
• 2 weeks = mature milk produced (90% water, 7% lactose, 2% fat, proteins, minerals & vitamins, Ca2+)

note: baby’s gut is able to absorb immunoglobulins whole; also receives passive immunity from placental transfer of maternal Ig
note: Ca2+ supports ossification of developing baby bones, so it is important that maternal calcium is sufficient

Question 3

How is lactation controlled?

Answer 3

High oestrogen:progesterone —> GROWTH of breast tissue
Low oestrogen:progesterone —> SECRETION

Prolactin stimulates secretion (itself inhibited by dopamine in the blood)

Suckling —> increased production of milk at next feed —> turgor of alveolar cells

No suckling —> turgor-induced damage to secretory cells (compression of blood vessels) —> cessation of milk production

Let-down reflex = suckling stimulates oxytocin release —> contraction of myoepithelial cells surrounding alveoli —> ejection of milk

Question 4

What are the advantages of breast feeding?

Answer 4

Bonding

Fewer infections in the baby

Question 5

How do the breasts change over life?

Answer 5

Prepubertal = few lobules (male & female breasts identical)

Thelarche = increased no. of lobules, increased volume of interlobular stroma

Menstrual cycle:

• follicular phase = lobules quiescent
• after ovulation = cell proliferation & stromal oedema (pre-menstrual pain)
• menstruation = decrease in size of lobules

Pregnancy = increase in size & no. of lobules, decrease in stroma, secretory changes

Cessation of lactation = atrophy of lobules (but not to former levels)

Increasing age = terminal duct lobular units decrease in number & size, interlobular stroma replaced by adipose tissue (therefore mammograms are easier to interpret in older women)