EM of part of a secretory alveolus in a lactating mouse mammary gland. Parts of two secretory cells line the alveolar lumen (above, left), which contains many micelles and flocculent material. Lateral cell borders have intercellular junctions (circle); basal nuclei are euchromatic. The cytoplasm holds rough endoplasmic reticulum (RER), Golgi complex (GC), mitochondria (Mi), dark globular micelles in large vesicles (Ve), and lipid droplets (Li). 10,000×.