Figure 2.

Ducts and alveoli in early pregnancy. Transverse section of ducts surrounded by a thick layer of collagenous (stromal) connective tissue containing fibroblasts and the fat pad. Also visible are small alveoli, which fill the fat pad by the time the gland lactates, but note that they are not surrounded collagen. A capillary is evident, and macrophages and mast cells are also present, though they require specific staining to visualize. A basement membrane is present directly at the basal surface of both ductal and alveolar epithelium (see Fig. 3).