More information about the breast

During the menstrual cycle the breast tissue responds to the circulating levels of the two hormones oestrogen and progesterone in different ways: oestrogen causes the acini to grow, and when the level of progesterone increases in the second half of the cycle (called the luteal phase, see the section on the female genital tract) the ducts also begin to develop - which is why many women find their breasts swollen and heavier towards the end of their cycle.

During breast feeding milk production is stimulated by the hormone prolactin which is secreted by the pituitary, and is maintained by a reflex initiated by the infant suckling: this also stimulates the pituitary to produce another hormone called oxytocin which makes muscles around each of the milk producing glands contract, thereby ejecting milk into the ducts. Problems associated with breast-feeding are discussed in the pregnancy section.

The breasts develop in the foetus as appendages to the skin, and occasionally enlarge and secrete a small amount of milk (called witches’ milk) shortly after birth. This is normal, and the enlargement disappears.