These contain many images which support the Lesson below. The gross anatomy of the mammary gland is covered in the Mammary Gland Anatomy Lesson. An Overview of Mammary Gland Histology Organization of Secretory Tissue Secretory tissue in the udder is organized into lobes, with each lobe made up of many lobules . Each lobule contains 150-220 microscopic alveoli .
Alveolus is the singular form and alveoli is the plural form of the word.
Alveoli are sack-like structures where milk is synthesized and secreted. An alveolus is the discrete milk producing unit. The lumen of the alveolus is lined by a single layer of secretory epithelial cells . The epithelial lining is surrounded by contractile myoepithelial cells . Myoepithelial cells contract in response to the hormone oxytocin, resulting in milk being squeezed out of the alveolar lumen and into the small ducts.