Lactation — Revision Notes

⚡ 30-Second Revision

Milk Synthesis: — Prolactin (Anterior Pituitary) $ightarrow$ Alveolar cells.
Milk Ejection: — Oxytocin (Posterior Pituitary) $ightarrow$ Myoepithelial cells contraction.
Inhibition during Pregnancy: — High Estrogen & Progesterone (Placenta).
Colostrum: — First milk, rich in IgA antibodies, low fat, yellowish.
Suckling Reflex: — Positive feedback for both prolactin and oxytocin release.
Mammary Glands: — Alveoli (production), Ducts (transport), Ampulla (storage).

2-Minute Revision

Lactation is the process of milk production and release from mammary glands. It's a post-parturition event, initiated by the sharp drop in estrogen and progesterone after placental expulsion, which removes the inhibition on prolactin.

Prolactin, from the anterior pituitary, is the 'milk-making' hormone, stimulating alveolar cells to synthesize milk. The 'let-down reflex,' or milk ejection, is mediated by oxytocin, released from the posterior pituitary in response to suckling.

Oxytocin causes myoepithelial cells to contract, squeezing milk into the ducts. The first milk, colostrum, is vital for neonatal immunity due to its high antibody content (IgA). Continuous suckling maintains lactation through a positive feedback loop, ensuring supply meets demand.

5-Minute Revision

Lactation, the physiological process of milk production and secretion, is crucial for infant nourishment. It involves the mammary glands, which develop significantly during pregnancy under the influence of estrogen and progesterone. However, these same hormones, produced by the placenta, inhibit actual milk synthesis until after childbirth. Upon placental expulsion, the dramatic fall in estrogen and progesterone removes this inhibitory block.

Milk Synthesis (Lactogenesis): The anterior pituitary gland releases prolactin, which acts directly on the alveolar epithelial cells (lactocytes) in the mammary glands, stimulating them to synthesize milk components like lactose, casein, and fats. Regular and effective suckling by the infant is key to maintaining high prolactin levels and thus continuous milk production, operating via a positive feedback mechanism.

Milk Ejection (Galactokinesis): This is the 'let-down reflex,' triggered by oxytocin from the posterior pituitary. Suckling stimulates nerve endings in the nipple, sending signals to the hypothalamus, which prompts oxytocin release. Oxytocin causes the myoepithelial cells surrounding the alveoli to contract, forcing milk into the lactiferous ducts and sinuses, making it available to the baby. This reflex can also be conditioned.

Milk Types:

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Colostrum: — The initial yellowish, thick milk (first few days), rich in proteins, vitamins, and crucially, antibodies (especially IgA) for passive immunity. It also aids in meconium passage.
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Transitional Milk: — Follows colostrum, gradually changing composition.
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Mature Milk: — Produced from about two weeks postpartum, it's thinner, whiter, and provides balanced nutrition (water, lactose, fat, protein, vitamins, minerals) for sustained growth.

Understanding the distinct roles of prolactin and oxytocin, the inhibitory effect of pregnancy hormones, and the immunological significance of colostrum are high-yield areas for NEET.

Prelims Revision Notes

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Definition: — Lactation is milk synthesis and secretion from mammary glands.
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Mammary Gland Structure:

* 15-20 lobes, each with alveoli. * Alveoli: Clusters of lactocytes (milk-secreting epithelial cells) surrounded by myoepithelial cells. * Alveoli $ightarrow$ Mammary tubules $ightarrow$ Mammary ducts $ightarrow$ Mammary ampulla (lactiferous sinus) $ightarrow$ Lactiferous duct $ightarrow$ Nipple.

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Hormonal Control:

* During Pregnancy: High Estrogen & Progesterone (from placenta) inhibit prolactin's action on mammary glands, preventing lactation. * After Parturition: Placental expulsion $ightarrow$ Drop in Estrogen & Progesterone $ightarrow$ Removal of inhibition.

* Prolactin (Anterior Pituitary): Primary hormone for milk synthesis (lactogenesis). Stimulates lactocytes. * Oxytocin (Posterior Pituitary): Primary hormone for milk ejection (galactokinesis/let-down reflex).

Stimulates myoepithelial cells to contract.

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Suckling Reflex (Neuro-hormonal):

* Suckling $ightarrow$ Sensory nerves in nipple/areola $ightarrow$ Hypothalamus. * Hypothalamus stimulates Anterior Pituitary to release Prolactin. * Hypothalamus stimulates Posterior Pituitary to release Oxytocin. * This is a positive feedback loop: more suckling $ightarrow$ more hormones $ightarrow$ more milk production/ejection.

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Types of Milk:

* Colostrum: First 2-5 days. Thick, yellowish. Very rich in IgA antibodies (passive immunity), proteins, vitamins. Low fat/lactose. Mild laxative. * Transitional Milk: Days 5-14. Gradual change from colostrum to mature milk. * Mature Milk: From 2 weeks. Thinner, whiter. High in fat, lactose. Provides balanced nutrition for growth. Contains some antibodies but less than colostrum.

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Key Functions: — Provides nutrition, immunity, aids in bonding, helps uterine involution in mother.

Vyyuha Quick Recall

Prolactin Produces Milk, Oxytocin Outputs Milk. (PPM, OOM)