Each breast is divided into lobes, like bunches of grapes, where the milk is produced. Each of these lobes contain 15 to 25 ducts or tubes to conduct the milk toward the nipple. Each duct widens on the way to your areola (the coloured area around the nipple) where the milk gathers before it is expressed.
Infra-red photographs of lactating breasts show that they grow hot in response to a baby's cry. This is when blood rushes to the breasts, bringing blood sugars to the milk glands. With sucking, oxytocin is released into your bloodstream, causing the star-shaped muscles cells around your milk glands to contract and squeeze out sweet-tasting milk. This squeezing is known as 'the let-down reflex'.
Even before this reflex occurs, some milk is waiting for your baby. This is called foremilk and it is both thirst-quenching and rich in protein. But the hindmilk that comes later has more fat and therefore more calories and satisfies the baby better.
Your let-down reflex must be stimulated for the milk supply to build up, but don't worry if you don't notice it happening. After a while, baby and breast work in harmony, with your milk supply matching their hunger. Let your baby set the pace for feeding. By letting him or her feed on demand, your body will respond by producing the correct supply. If you try to restrict the length of feeds, or top up with a formula feed, you won't make the right amount of milk.