In anatomical terms, the parenchyma of an body part refers to all the cells of that area that have an essential function. In the case of the breast parenchyma, these cells include the milk ducts and the glands that produce the milk. Apart from the parenchyma, fatty tissue is usually also present, the amount of which can vary with individual women. Certain diseases, such as breast cancer, can change the characteristics of the breast parenchyma.
Stroma is the scientific term for all of the tissue on the breast that is not part of the parenchyma. This is the fatty and connective tissue that gives the breast volume, and also provides an essential blood supply to the parenchymal cells of the breast. Each breast also has a system of ligaments that hold up the breast on the muscles of the chest. These are called "Cooper's ligaments," and are found throughout the breast, but end on the skin. This gives the breast its normal range of movement.
Much of the volume of the breast that is parenchymal tissue contains the lobules. These are the areas of the organs that produce milk for feeding a baby, and they are attached to ducts, which drain off the milk. Minor lactiferous ducts are small channels through which the milk flows into bigger major lactiferous ducts. From these major lactiferous ducts, the milk then travels into the major duct that is connected to the nipple. Babies receive their milk from the nipple, and the dark tissue around the nipple functions as a place for the child to latch on to.
All of the breast parenchyma, therefore, plays important roles in the function of the breast, whereas the stroma provides fat stores and supplies the blood supply to the breast cells. Even though blood is essential to the cells, this role is generalized to the rest of the body, and is not included in the parenchymal definition. Changes to the breast parenchyma, because of the important role it plays, can also signal onset of disease to doctors.
Medical technology has found that women have a normal range of density in their breast tissue. When the parenchymal tissues become altered, they can change in density, and this may be recognizable under imaging techniques such as a mammogram. Some cases of breast cancer are identifiable through alterations in parenchymal density, which may be beneficial to the treatment of patients.