Maternal Physiology and Anatomy Flashcards

A primiparous client who delivered 48 hours ago is concerned that her milk has not yet "come in." She reports her breasts feel soft and she is only able to express small amounts of thick, yellowish fluid. Which hormonal event is the primary trigger for the onset of copious milk secretion (Lactogenesis II)?

Answer: A sudden drop in progesterone levels following delivery of the placenta.

The onset of copious milk production, known as Lactogenesis II, is primarily triggered by the abrupt withdrawal of progesterone after the placenta is delivered. During pregnancy, high levels of progesterone inhibit the full secretory activity of prolactin on the breast's alveolar cells. Once the placenta is gone, progesterone levels fall dramatically, allowing prolactin to act on the prepared breast tissue and initiate abundant milk synthesis.

Which of the following correctly describes the function of the myoepithelial cells in the lactating breast?

Answer: They contract in response to oxytocin, squeezing milk from the alveoli into the ducts.

Myoepithelial cells are smooth muscle-like cells that form a basket-like network around the alveoli. The hormone oxytocin, released in response to infant suckling, causes these cells to contract. This contraction pressurizes the alveoli, ejecting the stored milk into the ductal system, a process known as the milk ejection reflex or 'let-down'.

A mother is exclusively breastfeeding her 4-month-old infant and has not yet resumed menstruation. This phenomenon, known as lactational amenorrhea, is primarily caused by the hormonal effect of:

Answer: Prolactin suppressing the release of gonadotropin-releasing hormone (GnRH).

High levels of prolactin, the primary milk-producing hormone, have an inhibitory effect on the hypothalamus, suppressing the release of gonadotropin-releasing hormone (GnRH). This, in turn, suppresses the pituitary's release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are necessary for ovulation and the menstrual cycle.

A breastfeeding mother reports that her right breast feels overly full and is producing less milk than her left breast, which her baby drains effectively at each feeding. This unilateral decrease in milk production is best explained by the local action of which substance?

Answer: Feedback Inhibitor of Lactation (FIL)

Feedback Inhibitor of Lactation (FIL) is a small whey protein present in breast milk that regulates milk supply on a local, autocrine level. When milk is not removed from the breast, FIL accumulates in the alveolar lumen and signals the secretory cells to slow down and stop milk synthesis. This is a protective mechanism to prevent over-fullness. Because it acts locally within each breast, it can explain why one breast might down-regulate production if it is not being drained effectively.

During pregnancy, the breasts undergo significant development in preparation for lactation. Which hormone is primarily responsible for the proliferation and branching of the lactiferous ducts?

Answer: Estrogen

During pregnancy, rising levels of estrogen stimulate the growth and branching of the milk duct system, creating the pathways for milk to travel. Progesterone works in concert with estrogen to promote the development of the milk-producing alveoli at the ends of these ducts.

A new mother is having difficulty with the milk ejection reflex. She reports feeling stressed and anxious during feeding times. The inhibition of which hormone is the most likely physiological reason for her difficulty?

Answer: Oxytocin

The milk ejection reflex (let-down) is mediated by the hormone oxytocin. The release of oxytocin from the posterior pituitary can be inhibited by stress, pain, anxiety, or embarrassment. This is because stress hormones like adrenaline can interfere with its release, temporarily preventing the myoepithelial cells from contracting and releasing the milk that is already present in the breast.