Breasts are hormonally regulated organs that mature and develop at during puberty in women. The increase of female hormones, such as estrogen and progesterone, induce the development of breasts--a process that continues throughout life and completes with pregnancy and lactation. The early development of breasts, which occurs during puberty, happens in a number of stages, which can be identified based on the appearance of the breast.
Enlargement of the Breast
The first stage in breast development is the formation of a mammary fat pad, which will support further growth of the breast. At this point, the breast is made up of fat and connective tissue, and does not contain the glandular tissue and lobules present in a mature breast. The breast will appear as a bud, with the breast and nipple slightly raised, and the areola around the nipple will become larger and darker in color. According to the Ohio State University Medical Center, these changes occur in response to an increase in circulating estrogen that occurs at the onset of puberty.
Formation of Secretory Glands
Once the fat pad and connective tissue have formed the bud required for breast growth, the secretory glands within the breast begin to develop. This process usually occurs after menstruation and ovulation have started, and involves the growth of lobules at the end of the ducts within the breast.
The increase in female hormones that occurs during puberty and throughout menstruation has an effect on breast growth. According to Cornell University, estrogen levels, which are high in some stages of the menstrual cycle, allow for growth of the breast tissue. Progesterone, which is higher during other stages of the cycle, promotes maturation of secretory glands. During the growth of secretory glands, the breast continues to get larger.
Further Growth and Maturation of the Breast
The breast will continue to grow larger, to develop an extensive branching system of lobules and ducts, connected to the nipple. During this time the breast will undergo morphological changes. In addition to appearing larger, the areola and nipple will become raised, forming a second mound on top of the breast.
As the breast continues to grow, the mound will disappear to form a mature breast with only the nipple raised. The size and texture of the breast can change slightly during the course of the menstrual cycle, but should not undergo another cycle of significant breast growth until puberty.
