Breast Milk

Breast Milk

  • complete nutrition for first 6 mo

  • dietary staple for first year

  • contains antibodies – passive immunity

Hormonal control


  • stimulates proliferation of glandular tissue

  • results in branching and lengthening of ductal system


  • promotes growth of lobes, lobules and alveoli

Increased revascularization of the breast tissue

Montgomery glands become more prominent

Nipple areola darkens

Progesterone antagonizes prolactin

At delivery –

  • progesterone and estrogen levels decrease

  • prolactin levels remain high

Following delivery –

  • decrease in placental lactogen

  • decrease in estrogen

  • decrease in progesterone

  • prolactin increases – results in alveolar cells secreting milk

Milk ejection pathway

  • areola stimulus

  • hypothalamus inhibits secretion of prolactin inhibitory factor

  • posterior pituitary gland releases oxytocin

  • oxytocin effects myoepithelial cells surrounding alveoli and ducts, causes them to contract initiating milk ejection


  • thick yellow fluid

  • present at delivery and for first few days post-partum

  • 67kcal/100ml vs 75 kcal/100ml of mature milk

  • has higher ash, sodium, K+, and Cl- than mature milk

  • higher protein, lower fat (2%) and lower lactose than mature milk

  • increased protein content due to immunoglobulins (esp IgA)

  • initiates bifidus factor of the infant digestive system (laxative properties to promote meconium passage)

Mature Milk

  • produced 14 d postpartum

  • high water content (90%)

  • low protein content than colostrum

  • high lactose content

  • higher fat content, carb and vitamin content than colostrum

  • high oligosaccarride and enzyme content

  • 75kcal/100ml

Breast Milk Proteins

  • 0.9% of milk is protein


  1. Casein

  2. serum albumin

  3. lactalbumin

  4. immunoglobulins

The whey:casein ratio is 60:40%

  • whey acidified in the stomach forming easily digestible curds

  • the casein in cow’s milk is of higher percentage and more difficult to digest

5 Major milk proteins

  1. alpha-lactalbumin: principle protein in the whey portion

  2. serum albumin: minor component

  3. lactoferrin: potent bacteriostatic iron binding capacity – inhibits the growth of iron dependent bacteria. Protects against Staph aureus, E. coli, and salmonella.

  4. Lysozomes: protects against E. coli and salmonella

Immunoglobulins – provides passive immunity. IgA, a major immunoglobulin, prevents bacteria and viruses penetrating mucosa.

Nucleotides: nitrogen compound, lowers bowel pH suppressing alkalineophilic pathogens


  • aids in fat breakdown and digestion

  • emulsify milk creating easily digestible curds


  • remain at constant levels at many phases during digestion

  • derived from glucose and are the main energy source


  • stimulates intestinal bacteria lactobaccilus bifudus that out-competes infectious bacterial strains

  • lactose content regulates milk volume

  • governs water volume required for the newborn to regulate its body temp

  • lactose facilitates Ca2+ and Fe2+ absorption

Vitamins – milk provides all essential vitamins, minerals and trace elements with the exception of vit D. Breast milk provides only small amounts of vit D. Supplementation of 400ul should continue until 1 yr

Vit E –

  • at high levels in colostrum

  • deficiency may result in hemolytic anemia

Vit A –

  • its pre-cursor betacarotene

  • colostrum contains twice as much as mature milk

Vit K –

  • component of blood coagulation

  • small amounts in milk

  • given IM to prevent newborn hemorrhage

  • within a few days after birth newborn manufactures sufficient vit K for clotting

  • milk promotes GI bacteria producing vit K

Water soluble vitamins in breast milk are dependent onf mother’s diet

despite low breastmilk calcium, infants absorb 67% of what is available

Iron –

  • present in small amounts

  • lactoferrin facilitates availablility

  • iron absorption facilitated by high lactose and vit C


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