Mammary Glands: Anatomy, Hormonal Control, and Lactation Physiology

Mammary glands are modified sweat glands unique to mammals, producing nutrient-rich milk for offspring. Their development and function are exquisitely hormone-regulated.

Anatomy

• 15–20 lobes per breast, each with 10–25 lobules.
• Lobules contain clusters of alveoli (milk-secreting acini) lined with lactocytes and surrounded by myoepithelial cells.
• Lactiferous ducts converge from lobules → lactiferous sinuses → nipple pores (5–9 per nipple).
• Supportive stroma: Cooper's ligaments, adipose tissue, blood/lymph vessels, nerves.

Hormonal Regulation

Hormone	Source	Primary Role
Estrogen	Ovary (pregnancy: placenta)	Ductal growth, branching
Progesterone	Ovary (corpus luteum → placenta)	Lobuloalveolar development
Prolactin	Anterior pituitary	Milk synthesis (lactogenesis)
Oxytocin	Posterior pituitary	Milk ejection (let-down)
hPL, cortisol, insulin	Placenta, adrenal, pancreas	Synergistic preparation

Lactation Stages

1. Mammogenesis (puberty–pregnancy): Ductal/alveolar growth.
2. Lactogenesis I (mid-pregnancy): Colostrum production begins; progesterone inhibits full secretion.
3. Lactogenesis II (postpartum, 30–72 hrs): Progesterone withdrawal + high prolactin → copious milk.
4. Galactopoiesis (maintenance): Prolactin + oxytocin + local autocrine control (FIL). Demand drives supply.
5. Involution (weaning): Apoptosis, tissue remodeling → pre-pregnancy state.

Milk Composition

Dynamic: colostrum (IgA, leukocytes, low fat/lactose) → transitional → mature (foremilk: watery, lactose-rich; hindmilk: fat-rich). Adapts to infant age, time of day, maternal diet.

Clinical Relevance

• Lactation suppresses ovulation (lactational amenorrhea) via prolactin inhibition of GnRH.
• Breast cancer risk reduced with longer cumulative breastfeeding.
• Mastitis, low supply, oversupply—common clinical issues managed with lactation support.

The breast is a remarkable endocrine organ, dynamically responsive to reproductive status and infant demand.