A comparison of the three stages of breast development is shown in this image. The inactive breast is on the left; the breast during pregnancy is in the middle; and the breast during lactation is on the right. 100x, 100x, 100x
The breast during the inactive stage can be identified in two ways. First, by the abundance of interlobular connective tissue and ducts; secondly by the lack of acini and secretory product.
During pregnancy the ducts branch and grow; acini form from the ducts. Interlobular connective tissue decreases as the secretory components increase.
During lactation the breast reaches maximal development. Acini are widely distended and milk products can be seen dilating the acini and ducts. The relative abundance of the interlobular connective tissue is reduced as the secretory components increase in size and number.