Maternal and Infant Anatomy and Physiology
The Maternal and Infant Anatomy and Physiology domain tests how breast structure, endocrine control, and infant oral anatomy produce successful lactation. Exam items typically link a clinical sign to a mechanism rather than ask for isolated facts.
Maternal breast structure
- The alveolus is the functional unit: lactocytes synthesize milk, and myoepithelial cells contract under oxytocin to eject it.
- Milk flows through branching lactiferous ducts. The breast is not a storage sac; most milk is synthesized in response to removal, and storage capacity varies.
- Blood supply is mainly internal thoracic and lateral thoracic arteries; lymph drains to axillary, internal mammary, and supraclavicular nodes.
- The nipple-areolar complex is innervated by intercostal nerves T3-T5, with the lateral cutaneous branch of T4 a major contributor.
Endocrine sequence
- Lactogenesis I begins in midpregnancy. High placental progesterone prevents full secretory activation.
- Lactogenesis II, secretory activation, occurs around days 2-5. Progesterone withdrawal plus prolactin, insulin, cortisol, and thyroid hormone allows copious milk.
- Lactogenesis III, galactopoiesis, depends on frequent removal. Feedback inhibitor of lactation (FIL) in milk slows synthesis when milk remains in the breast.
- Prolactin from anterior pituitary lactotrophs is tonically inhibited by dopamine; suckling reduces dopamine. Oxytocin from the posterior pituitary causes milk ejection.
Infant anatomy
- The newborn has buccal fat pads, a small mandible, and a tongue that must elevate and groove. A high larynx helps protect the airway during swallow.
- Suck-swallow-breathe coordination depends on cranial nerves V, VII, IX, X, and XII. Preterm or hypotonic infants may fatigue before transferring adequate milk.
Worked example
A mother has retained placental fragments after a home birth. On day 3 her breasts are soft, she expresses under 5 mL of colostrum, and her infant has lost 9.5% of birth weight. The reasoning: lactogenesis II requires progesterone withdrawal after placental delivery. Retained tissue keeps progesterone elevated and delays secretory activation. Insufficient glandular tissue is not the first hypothesis. The plan is to evaluate and treat retained products, support frequent milk removal, and monitor the infant.
Traps that cost marks
- Confusing prolactin, which supports synthesis, with oxytocin, which causes ejection.
- Claiming a breast can be completely emptied; milk is continuously produced.
- Treating nipple pain as normal instead of assessing latch and oral anatomy.
- Assuming breast size predicts supply; small breasts can produce fully.