Mammary Gland
(Lactating)

Mammary glands are compound, tubulo-alveolar glands whose structure changes depending on the reproductive status of females.

Lactating Mammary Gland - during pregnancy the mammary gland undergo morphologic and functional maturation.

• Lobes - 15 to 20 lobes separated by septae of connective tissue with adipose cells.
• Lactiferous Duct - each lobe is drained by a single lactiferous duct that opens into the nipple. It is lined by a double layer of cuboidal or columnar cells surrounded by a sheath of connective tissue with myoid cells.
• Lobules - enclosed by a thin layer of connective tissue.
• Intralobular Ducts (#1, #2 and #3)- lined by one or two layers of cuboidal cells surrounded by a thin layer of connective tissue.
• Terminal Ductules (#1 and #2) - branches of intralobular ducts lined with cuboidal secretory cells.
• During pregnancy, they differentiate into secretory alveoli that produce milk.
• Alveoli (#1 and #2) - grow and expand during pregnancy and lactation.
• Simple Epithelium - cuboidal or columnar secretory cells that synthesis and secrete milk.
• Milk - the eosinophilic material within the alveolar lumen and ducts is proteins from secreted milk.
• Intralobular Stroma - loose connective tissue with few adipose cells.

Mammary Gland
(Resting)

Inactive (Resting) Mammary Gland - is composed of the duct system but no alveoli. This specimen is from the region that surrounds the nipple.

• Lactiferous Ducts - each lobe is drained by a single lactiferous duct that opens into the nipple. It is lined by a double layer of cuboidal or columnar cells surrounded by a sheath of connective tissue with myoid cells.
• Terminal Ductules - branches of intralobular ducts.
• Simple Cuboidal Epithelium - myoepithelial cells and fibroblasts surround the ducts..
• Lamina Propria - dense connective tissue with numerous bundles of smooth muscle whose contraction allows for erection of the nipple.