Lactation

Mammaries are why we call her Mama

Mechanism of afterpains• The mother is encouraged to allow the baby to suckle soon

after birth, even though milk production is inhibited by the presence of residual progesterone in the mother’s body – the level of P will gradually diminish because the source, the placenta, is now gone. Milk may not be available for 2 days or more…

• Colostrum is already available in the breasts and when the baby suckles, it provides valuable antibodies, some nutrients, and fluid.

• The stimulation of the nipples in suckling acts on nerve endings that cause oxytocin to be delivered from the mother’s posterior pituitary. This also causes contractions of the uterus called afterpains that are good pains, because they cause the uterine muscle to contract, which reduces bleeding and helps the uterus to return to normal size (involution: a process that takes 4-6 weeks) sooner than it otherwise will.

Factors involved in milk production and milk letdown

• In nonpregnant women (and males), prolactin secretion is tonically inhibited by dopamine (d2 receptors). This inhibition is relieved by the hypothalamus during pregnancy.

• During pregnancy, estrogen, progesterone, prolactin and placental lactogen prepare breasts for lactation, but progesterone also inhibits actual milk secretion.

• After loss of the placenta, oxytocin is released from the post. pituitary reflexively with suckling – it causes milk letdown. This is a conditionable reflex.

• Suckling maintains prolactin secretion- prolactin supports milk production and also may promote maternal behavior.

Ideally, the postpartum period is for bonding

• Bonding is a part of human nature, and does not require breastfeeding, but it certainly is facilitated by this mode of continuing the mother-child interdependency.

• The hormonal regulation of brain changes that promote care of the young is most closely associated with prolactin – in both sexes. The mother who breastfeeds will have prolactin released in response to nipple stimulation. In the case of males, those fish, birds and mammals in which the male takes part in care of the young, all show increases in prolactin during the care period. Studies of tamarins and marmosets, among the primates, have shown that prolactin levels rise before the birth of the young, and so the males are “primed” for their roles.

What is in human milk

• Lactose 7.3 g/dl• Oligosaccharides: 1.2 g/dl• Protein: 0.8 g/dl• Triacyglycerols: 4%• Phospholipids: 0.04%• Na+: 5 mEq/l• K+: 15 mEq/l• Cl-: 15 mEq/l• Ca++: 16.0 mEq/l• Mg++: 2.8 mEq/l

• The milks of various mammalian species are quite different from each other. For example, the carbohydrate content of bovine milk is lower than that of human milk and the protein and mineral contents are higher. These differences affect its digestibility by human babies (remember, cows have 3 stomachs to our 1).

The sequence of delivery• When women examine their own milk,

especially the first milk that is delivered in a feeding, they are negatively impressed by its weak appearance:

• Foremilk is low-fat, with proteins and carbohydrates.

• Hindmilk is fattier, creamier, and provides a satisfying completion of the nursing experience.

the hypothalamus knows best

Hypothalamus

↓dopamine secretion↑ oxytocin secretion

Ant pituitary lactotrophs

↑ prolactin secretion

Ant Pituitary luteotrophs

↓LH secretion

Ovary

Follicle maturation inhibited

Milk production maintained

Milk letdown

↓ GnRF secretion

SUCKLING

Multifunctional oxytocin

• Labor contractions

• Mother-infant bonding in minutes-hours after birth

• Regression of uterus after delivery

• Milk letdown (more bonding?)

• Orgasm contractions male/female

• Male-female bonding (?)

The contraceptive effect of breast-feeding: breast-feed, don’t breed

• Contraceptive effect of lactation is diminished by – Loss of nighttime feedings– Diet supplementation

Bottle-feeding: cycling begins 8 weeks after delivery; ovulation begins 11 weeks after delivery

Breast-feeding: cycling begins at about 33 weeks; ovulation at 36 weeks – no woman ovulates who breast-feeds six or more times daily for a total of 60 min, and who does not supplement child’s diet with formula (‘daddy’s milk’).

Superior properties of breast milk

• No potentially unclean containers or formula water needed – so less diarrheal disease

• Inexpensive• Prewarmed to correct temperature• Promotes mother-child bonding • Milk letdown helps uterus return to non-pregnant size

(oxytocin effect)• Transfers maternal antibodies and growth factors• Iron is complexed with lactoferrin, making it more

available than it would be as an inorganic salt• Less likely to provoke food allergies • Direct relationship between duration of breast-feeding

and child’s IQ – 6 months of breast feeding = 8 IQ points.

Breastfeeding transfers immunity: the immunoglobulins. Secretory IgA is the dominant antibody in milk

• Breastfeeding benefits for the baby:• 1. Ideal nutrient mixture• 2. bonding, body-contact time with mother• 3. Passive immunity, both antibodies and

white blood cells are transferred, resulting in fewer childhood illnesses

• 4. Fewer food allergies• 5. Immune system development promoted• 6. Brain development controlled studies

indicate a boost of 8 IQ points for breastfeeding 6 months

A Downside - Lactation can channel environmental toxins to the infant

• Many drugs and toxins that circulate in maternal bloodstream may also be secreted in milk.

• Fat-soluble toxins that have accumulated in maternal fat may be released into the blood by fat breakdown during lactation – these may then be transferred to the nursing infant.