Breast Anatomy & Physiology - Lactation

Prolactin causes the production of milk, and oxytocin release (via the suckling reflex) causes the contraction.

Reproductive hormones are important in the development of the breast in puberty and in lactation. Estrogen promotes the growth of the gland and ducts, while progesterone stimulates the development of milk producing cells. Prolactin, released from the anterior pituitary gland, stimulates milk production. Oxytocin, released from the anterior pituitary gland, stimulates milk production. Oxytocin, released from the posterior pituitary in response to suckling, causes milk ejection from the lactating breast.

The breasts become fully developed under the influence of estrogen, progesterone and prolactin during pregnancy. Prolactin causes the production of milk, and oxytocin release (via the suckling reflex) causes the contraction of smooth muscle cells in the ducts to eject the milk form the nipple.

The first secretion of the mammary gland after delivery is colostrum. It contains more protein and less fat than subsequent milk, and contains antibodies that impart some passive immunity to the infant. Most of the time it takes 1 – 3 days after delivery for milk production to reach appreciable levels.

The expulsion of the placenta at delivery initiates milk production causes the drop in circulating estrogens and progesterone. Estrogen antagonizes the positive effect of prolactin on milk production. The physical stimulation of suckling causes the release of oxytocin and stimulates prolactin secretion, causing more milk production.