Physiology of Lactation

2.  Changes during pregnancy
 Increased breast tissue
 Maturation of structure
 Hormonal controls
 Prolactin: stimulates milk
production
 Oxytocin: stimulates milk release
 “let-down” reflex

3.  Suckling stimulates nipple
--->pituitary gland secretes
oxytocin--->let down reflex
results in milk ejecting cells
contract forcing milk from
milk cells into milk ducts.
 Milk pools in lactiferous
sinuses under the areola.
Suckling stimulates milk to
come from the nipple.
Hypothalamus
Prolactin
Lacteal
Uterus
Oxytocin
Myoepithelial
Cell
Pituitary Gland

4. Milk
production
Milk
ejection
Prolactin Oxytocin
Anterior
pituitary
Posterior
pituitary
Hypothalamus

5. 5
Anatomy of breast during
pregnancy

7.  Mammogenesis
› Mammary (breast) growth occurs. The
size and weight of the breast increases.
› Preparation for milk production
› Starts at puberty and continues until
third trimester of pregnancy
› Ductal proliferation –estrogen
› Lobuloalveolar development -
progesterone

9. Stage 1 (late pregnancy):
Alveolar cells are differentiated from secretory cells.
Stage 2 (day 2 or 3 to day 8 after birth):
 By day 4-5 days postpartum, estrogen and progesterone
levels have dropped and thus;
 Acinar cells develop into secretory cells
 The tight junction in the alveolar cell closes.
 Milk secretion begins.
 Breasts are full and warm.
 Endocrine control switches to autocrine (supply-demand)
control

10.  Causes alveolar cells to initiate milk
secretion
 Stimulate glandular production of colostrum
(which is initial milk produced characterized
by a yellow color and thick texture)
 Acts synergistically with cortisol to stimulate
milk production
 Prolactin “surges” occur within 15 minutes of
nipple stimulation

11. Ejection of Milk-(Oxytocin)
 Primary function is milk ejection
 Contracts myoepithelial cells located around the
alveolar cells and the glandular ducts.
 Milk expelled from alveoli into ducts and
subareolar sinuses that lead to the nipple pore.
 Oxytocin is produced in response to suckling
effect.

12. Cont.
Suckling infant stimulates touch receptors densely
located around the nipple and areola.
Sensations create impulses that activate dorsal root
ganglia via the intercostals nerves.
Impulses ascend the spinal cord, creating an afferent
neuronal pathway to both the paraventricular nuclei of
the hypothalamus where oxytocin is synthesized and
secreted by the pituitary gland.
Stimulation of nuclei causes release of oxytocin down
the pituitary stalk and into the posterior pituitary gland,
where oxytocin is stored.

14. Maintenance of Lactation
› later than day 9 after birth to beginning of
involution
› Established secretion is maintained
› Autocrine system control continues
› Stimulated by milk removal
 Regular synthesis and release of prolactin and
oxytocin
 Stored milk causes increased intramammary
pressure which limits nutrient and hormonal
supply to the mammary gland

15.  Moves milk from lobules to sinuses, so baby
can eat
 Inhibited by stress, pain, anxiety
 Triggered by sound, smell, sight of infant
Let Down:
Ejection, not suction, moves milk
to the areola

16.  Infant grasps
most of the areola
in his mouth
 Tongue “milks”
milk to the back
of the mouth prior
to swallowing.
Latch: The baby’s tongue moves milk from
areola to nipple.

17.  Milk in lobules contains
whey protein called
Feedback Inhibitor of
Lactation (FIL)
 If milk is not removed,
and lumen is full,
production will
decrease
 Goal: 10-12 feeds in 24
hours, until baby is
done.
Moving Milk: Demand drives supply.
Negative
feed back

18. Latch
Moving
Milk
Let
Down
Breastfeeding
Success

20.  While breastfeeding results in amenorrhea
and delays the return of fertility, the length
of the delay cannot be reliably predicted or
detected
 Most lactating women will resume menses
within 6–9 months
 Prolactin has a negative effect on secretion of
GnRH and the gonadotropins

21.  Don’t drink alcohol
 Don’t take medications unless OK by Medical
Provider
 Don’t take illegal drugs
 Don’t smoke
 Don’t get into environmental contaminants
 Don’t have caffeine
21

22. Anxiety
o Increased catecholamine production will lead to
Vasoconstriction and reduction of oxytocin delivery to
the myoepithelial cells
Combination birth control pills
Mainly estrogen
Smoking
Nicotine – inhibits prolactin synthesis and secretion
Inadequate dietary intake