Breast morphological changes with pregnancy and lactation

(A) Pregnancy hormones induce hyperplasia of TDLUs. This image depicts the changes in a woman who is five months pregnant. Note the enlarged lobules have crowded out the extralobular connective tissue.

(B) Low-magnification image of a lactating mammary gland of a young woman. Note that the alveoli fill the entire mammary gland without evidence of residual fat cells.

(C) TDLUs of the lactating mammary gland of a young woman. Medium magnification.

(D) Lactating mammary gland of a young woman. Note that the lumens are filled with a proteinaceous fluid with clear lipid vacuoles. The epithelium is attenuated.

(E) Lactating mammary gland of a young woman showing lumens filled with fluid. The tall columnar cells have clear lipid vacuoles.