Lactation Notes

Breast Structure and Changes

• Breast: Modified sweat gland.

• Location: Anterior chest wall.

• Lobes: 15-20 per breast.

• Pregnancy changes: Controlled by E, P, PRL, hPL.

• Lactation: Controlled by prolactin and oxytocin.

• Lobule development: Permissive role of insulin and cortisol.

Key Processes in Lactation

• Mammogenesis: Growth of mammary glands.

• Lactogenesis: Milk production initiation (high prolactin, ↓ E & P).

• Galactopoiesis: Milk production maintenance (secretion & ejection).

Lactogenesis

• Depends on presence of high levels of prolactin + withdrawal of estrogen + progesterone

• After parturition —> prolactin levels fall, but more slowly

• In the absence of suckling, milk secretion will last for 3-4 weeks

Prolactin

• Stimulates: Mammogenesis & milk secretion.

• Produced in: Anterior pituitary.

• Forms:

  • Non-glycosylated: Acute stimuli.

  • N-glycosylated: Main circulating form.

Galactopoiesis - Milk Secretion

• Process: Synthesis & transport of milk constituents.

• Stimulated by: Prolactin (suckling).

• Prolactin Action:

  • ↑ Amino acid uptake.

  • Gene transcription for milk proteins.

  • Enzymes for lactose synthesis.

  • Fatty acid & phospholipid synthesis.

Suckling and Prolactin Release Mechanism

1. Suckling: Stimulates sensory nerves.

2. Nerves: Synapse in spinal cord.

3. Signals: To hypothalamus (arcuate nucleus).

4. Dopamine: Release inhibited.

5. Prolactin: Released, stimulates milk production.

Galactopoiesis - Milk Secretion

• Involves: Passive removal & ejection.

• Oxytocin: Stimulates myoepithelial cell contraction.

• Result: Milk ejection.

Oxytocin

• Crucial for: Milk ejection & uterine contraction.

• Synthesized: Hypothalamus.

• Released from: Posterior pituitary.

Suckling and Oxytocin Release Mechanism

1. Suckling: Stimulates sensory nerves.

2. Nerves: Synapse in spinal cord.

3. Signals: To hypothalamus (paraventricular & supraoptic nuclei).

4. Oxytocin: Produced & released.

5. Effect: Contraction of myoepithelial cells, milk ejection.

Factors Affecting Oxytocin Release

• Conditioned by: Stimuli; inhibited by stress.

• Requirement: Calm environment.

Infant's Role in Milk Expression

• Action: Draws nipple & areola to form teat.

• Compression: Between tongue & hard palate.

Lactation and Inhibition of the Ovarian Cycle

• Suckling: Inhibits ovarian cycle.

• Result: ↓ GnRH production.

• Inhibition: FSH & LH release.

• Role of Prolactin: Inhibits ovulation.

Contraceptive Effect of Lactation

• Lactational Amenorrhea: Prevents menstruation.

Lactational Amenorrhea Method (LAM) Effectiveness

• Failure rate: ~2% (<6 months postpartum, fully breastfeeding, amenorrheic).

Composition of Breast Milk

• Colostrum: Differs from mature milk.

• Mature Milk Contents:

  • Water: $90$ g%

  • Lactose: $7$ g%

  • Fat: Essential fatty acids.

  • Protein: Lactalbumin & lactoglobulin.

  • Minerals: Calcium, Iron, etc.

  • Vitamins: A, B, C, D, E, K.

  • Energy: ~$70$ kcal/$100$ mL

Recommendations for Breastfeeding

• WHO: Exclusive breastfeeding for 6 months, up to 12 months.

• NHMRC: Exclusive breastfeeding until ~6 months, continue to 12+ months.

Australian National Breastfeeding Strategy

• Aim: Environment valuing breastfeeding.

• Objectives: Increase exclusive breastfeeding rates to 40% (2022) & 50% (2025) for 6-month-old babies.

Breastfeeding Prevalence in Australia (2022)

• $90.6$% ever received breast milk (0-3 years).

• Exclusive Rates:

  • 2 months: $73.5$%

  • 4 months: $63.9$%

  • 6 months: $37.5$%