BREAST CANCER SERIES 1: Knowing The Breasts The breasts are secondary sex characteristics of females but are also present in rudimentary form in males. The female breasts begin to develop during puberty due to the production of the hormone estrogen and growth hormones. The breast is a modified sweat gland. The breast consist of mammary gland , which is made up of a number of ducts and secretory lobules. Each lobule is made of tiny, hollow sacs called alveoli , which drain into a single lactiferous duct (milk duct). The milk duct serves as the passageway of the milk from the lobules to the tiny holes in the nipple . The dark area of skin surrounding the nipple is known as the areola . Newborns do not see quite well so the areola which becomes darker after birth helps them find their source of food. This illustration shows major parts of the human female breasts. The mammary glands are lined by cells known as myoepithelial cells which have the ability to contract to rel