Explain the Physiology of Lactation

Lactogenesis is the onset of copious milk secretion around parturition, triggered by a fall in plasma progesterone levels. Although some colostrum is secreted after delivery (2-3 days), full lactation begins later. The first 2-3 days after delivery is a period of rapid lactation initiation, followed by the longer period of maintenance of lactation. This complex neuroendocrine process is facilitated by interplay of various hormones. Oxytocin and prolactin instigate the lactation process, Prolactin is responsible for milk production and oxytocin is involved in milk ejection from the breast. The basic secretory units of the mammary gland, as you may already know now, are the alveoli composed of a single layer of epithelial cells. The alveoli produce the secretory product.

Surrounding the alveoli are the myoepithelial cells which are contractile and are responsible for the ejection of milk from alveoli and alveolar ducts. A cyclic process of secretory activity, luminal distention and expulsion of milk into the duct system continues throughout lactation as directed by the suckling of the infant and the letdown reflex.

Regular sucking stimulates the continuation of milk secretion. Milk removal from the breast is a product of coordinated interaction between suckling of the infant and letdown reflex of the mother. As the infant commences suckling, afferent impulses generated in the receptors in the areola travel to the brain where they stimulate the release of oxytocin from the posterior pituitary. Oxytocin travels through the blood stream to the breast where it combines with specific receptors on the myoepithelial cells, stimulating them to contract and force milk from the alveoli into the mammary ducts and sinuses.