Lactation: Physiology

In pregnancy

• Second trimester - colustrum appears in acinar glands, by 3rd trimester breast alveoli contains significant amounts of colustrum
• In pregnancy, milk is not produced - high progesterone/oestrogen levels inhibit the active secretory effects of prolactin on mammary alveolar epithelium

Post birth

• Decrease in oestrogen and progesterone - prolactin levels can now stimulate acinar cells to secrete colustrum
• Sucking on nipple = prolactin stimulates sensory receptors that activate nerve impulse = reduction in PIF
• Let down reflex - Sucking causes oxytocin release. Becomes conditioned response in lactating women, requiring only visual/conscious thought
  • Oxytocin = contraction of myoepithelial cells = release of milk into lactiferous ducts and sinuses

Galactopoeisis

1. Regular sucking
2. Regular emptying
3. Demand feeding

Breast milk components

Colustrum (first milk):

• Yellow, viscous fluid, high in carbohydrates proteins antibodies, low in fat
• Lymphocytes, monocytes
• Interferon: stimulates removal of meconium & stimulates beneficial lactobacillus growth in intestines

Mature breast milk:

• Fat (3-5%), protein (0.8%), carbs (7%)