What are the primary hormones involved in lactation and what are their roles?

The two primary hormones are prolactin and oxytocin. Prolactin, secreted by the anterior pituitary gland, is responsible for the synthesis and production of milk by the alveolar cells in the mammary glands. Oxytocin, released from the posterior pituitary gland, causes the contraction of myoepithelial cells surrounding the alveoli, leading to the ejection or 'let-down' of milk. Estrogen and progesterone, high during pregnancy, inhibit prolactin's action, preventing lactation until after childbirth.

What is colostrum and why is it important for a newborn?

Colostrum is the first milk produced by the mother, typically for the first few days after delivery. It is thick, yellowish, and highly concentrated. Its importance lies in its rich composition of proteins, vitamins, and especially antibodies (immunoglobulins like IgA). These antibodies provide crucial passive immunity to the newborn, protecting it from various infections. Colostrum also acts as a mild laxative, aiding in the expulsion of meconium and preventing jaundice.

How does suckling stimulate milk production and ejection?

Suckling is a critical stimulus for both milk production and ejection. When a baby suckles, sensory nerves in the nipple and areola send signals to the mother's hypothalamus. This stimulates the anterior pituitary to release prolactin, which promotes milk synthesis. Simultaneously, it triggers the posterior pituitary to release oxytocin, which causes the myoepithelial cells to contract, ejecting the milk. This forms a positive feedback loop, where increased suckling leads to increased milk supply.

What is the 'let-down reflex' and what triggers it?

The 'let-down reflex,' also known as the milk ejection reflex, is the process by which milk is released from the mammary alveoli into the ducts, making it available to the baby. It is primarily triggered by the hormone oxytocin. The main stimulus for oxytocin release is suckling by the infant. However, it can also be triggered by conditioned responses, such as hearing a baby cry, seeing the baby, or even thinking about the baby, due to the neuro-hormonal connection.

How does the body prevent lactation during pregnancy?

During pregnancy, high levels of estrogen and progesterone, primarily produced by the placenta, act as inhibitors of lactation. While prolactin levels are high throughout pregnancy and the mammary glands are developing, these placental hormones block the receptors for prolactin on the alveolar cells, preventing them from synthesizing and secreting milk. Only after the expulsion of the placenta at childbirth, when estrogen and progesterone levels drop sharply, can prolactin exert its full milk-producing effect.

Lactation

Biology

NEET UG

Version 1Updated 22 Mar 2026

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Lactation is the physiological process in mammals, including humans, by which milk is synthesized and secreted from the mammary glands. This complex biological function is primarily regulated by a delicate interplay of hormones, notably prolactin and oxytocin, which orchestrate milk production (lactogenesis) and milk ejection (galactokinesis), respectively. It is a crucial post-parturition event, …

Quick Summary

Lactation is the process of milk production and secretion from the mammary glands in mammals, essential for nourishing the newborn. It commences after childbirth, following the expulsion of the placenta, which causes a sharp decline in inhibitory hormones like estrogen and progesterone.

The primary hormone for milk synthesis is prolactin, secreted by the anterior pituitary, which stimulates alveolar cells to produce milk components. Milk ejection, or the 'let-down reflex,' is mediated by oxytocin, released from the posterior pituitary in response to suckling.

Oxytocin causes myoepithelial cells around the alveoli to contract, pushing milk into the ducts. The first milk, colostrum, is rich in antibodies, providing crucial immunity. Mature milk provides balanced nutrition.

This entire process is a neuro-hormonal reflex, maintained by a positive feedback loop where suckling ensures continued milk supply.

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Key Concepts

Hormonal Control of Milk Synthesis (Prolactin)

Prolactin is the cornerstone hormone for milk production. During pregnancy, its levels steadily rise, but its…

Hormonal Control of Milk Ejection (Oxytocin)

While prolactin makes the milk, oxytocin gets it out. The milk ejection reflex is a rapid neuro-hormonal…

Role of Colostrum in Neonatal Immunity

Colostrum is not just 'first milk'; it's a potent immunological cocktail. It is particularly rich in…

Milk Synthesis: — Prolactin (Anterior Pituitary)

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Alveolar cells.

Milk Ejection: — Oxytocin (Posterior Pituitary)

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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).

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