Lactation and Neonatal Growth

Question 1

What are the 4 stages of lactation?

Answer 1

1. Mammogenesis
   - growth of breast tissue
2. Lactogenesis:
   - initiation of milk secretion
   - divided into stage 1 (late pregnancy) and stage 2 (after birth)
3. Galactogenesis:
   - maintenance of milk secretion after initiation
4. Involution:
   - regression of mammary glands following weaning

Question 2

Explain mammogenesis in detail:

Answer 2

• At puberty the lactiferious ducts branch and form solid ends
• Estrogen and progeterone induce a low level of ductal-lobular-alveolar growth and an increase in fat deposition and connective tissue

2. Early pregnancy:
   - Increase in hypertrophy of ductal-lobular-alveolar system
   - Formation of lobes and growth of alveoli
3. Mid pregnancy:
   - Alveoli enlarge and acquire lumen
   - Alevolar cells differentiate: epithelial alveolar cells and myoepithelial cells

Question 3

Explain lactogenesis in detail:

Answer 3

Stage 1: cellular and enzymatic differentiation of mammary epithelium

Stage 2: Initiation of secretion of copious quantities of milk

• Triggered by hormonal stimulus: high prolactin and removal of progesterone and estrogen inhibition (after removal of placenta)
• The control of milk eventually moves from being hormonally triggered to supply and demand based on neuroendocrine reflex arcs

Question 4

Describe galactopoiesis in detail:

Answer 4

• Galactopoiesis is the maintenance of milk secretion and ejection after it has been established
• It is due to prolactin acting on prolactin receptors on alevolar epithelial cells stimulating milk secretion and oxytocin acting on oxytocin receptors on myoepithelial cells and smooth muscle cells of mammary ducts causing milk ejection

Question 5

Describe the prolactin neuroendocrine relflex:

Answer 5

1. The baby suckles on the nipple and stimulates mechanoreceptors of afferent nerves
2. The afferent nerve fibre stimulation is transmitted up the spinal cord via the brain stem and into the hypothalamus
3. The hypothalamus signals the anterior pituitary to secrete prolactin
   - stimulated by vasoactive intestinal polypeptide (VIP), prolactin releasing factor (PIF) and thyroid releasing hormone (TRF)
   - inhibited by dopamine and estrogens
4. Prolactin in the blood then acts on prolactin receptors on the alveolar epithelial cells within the mammary glands
5. Milk is then produced and secreted by the alveolar epithelial cells

Question 6

Describe the oxytocin neuroendocrine reflex:

Answer 6

1. Suckling or other stimuli of the nipple innervates mechanoreceptors of afferent nerves
2. The afferent nerve stimulation is transmitted up the ascending spinal cord tracts, through the brain stem and into the hypothalamus
3. The hypothamus then releases factors via the hypothalamo-hypophyseal tract that stimulate cells in the posterior pituitary to secrete oxytocin into the blood stream
4. Oxytocin then acts on myoepithelial cells in the alevoli and smooth muscle cells surrounding the mammary ducts causing the ejection of milk

Question 7

Describe involution in detail:

Answer 7

• The return of mammary tissue to non-pregnant/non-lactating state
• Process takes about 3 months
• Absence of suckling results in lower levels of prolactin
• Decreased prolactin causes decrease in milk production and atrophy of epithelial structures

Question 8

What are the benefits of breast milk?

Answer 8

• Provides baby with passive immunity from maternal antibodies
• Caters for the babies specific nutritional needs
• Has emotional and psychological benefits
• Cognitive benefits
• Linked to lower incidence of SIDS, stomach viruses, ear infections, asthma and juvenile diabetes
• convenient and cost effective
• linked to lower food intolerance/allergies in children
• helps with post-partum weight control